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Paper 13 - Session title: Poster Session 1
Tuesday-109 - Mass balance of the mountain glacier detecting by InSAR method
Zhou, Jianmin; Li, Zhen Institute of Remote Sensing and Digital Earth,CAS, China, People's Republic of
Show abstract
Abstract The mountain glacier changes are believed to currently provide significant responses to global climate change and strongly influence human welfare in this arid or semi-arid region, where water supplies are predominantly from glacier melt. Meanwhile, glacier mass balance has direct contribution sea level rise, declining water resources, runoff and disaster of glacier lake outburst. So the accurate estimation of mass balance at high spatial and temporal resolution becomes very important. Although traditional ground-based techniques exist for measuring glacier mass balance directly and inter-annually, they tend to be labor-intensive, expensive and provide very limited spatial coverage. Synthetic Aperture Radar (SAR) observations offers direct means of monitoring changes in surface elevation over the mountain glacier and can achieve centimeter-level accuracy.
This study describes the generation of a thickness changes map of the mountain glacier using SAR observations. We utilized observations of the glacier surface deformation to derive the thickness changes and then calculated the mass balance. We apply the method to Koxkar glacier (41.42︒N-41.53︒N and 79.59︒E-80.10︒E) in Tianshan Mountains, China, which is a typical Tuomuer-type glacier originating from Mt. Koxkar (6,342 m a.s.l.), and flows southeast to the terminus of 3,020 m a.s.l. The glacier extends 25.1 km in length and covers an area of 83.56 km2. The equilibrium line occurs at 4,300 m a.s.l. in the icefall from whose foot a 15.5-km-long, debris-mantled glacier tongue appears. The supraglacial debris covers an area of about 19.5 km2, which accounts for 83% of the total ablation area, with thicknesses ranging from less than 0.01 m on the upper reach of the ablation area and on ice cliff faces to more than 3.0 m near the glacier snout.
Due to the gap of the SAR observations, we only derive the mass balance of the ablation area of the Koxkar glacier (from 3800 m to 3100 m). We reveal that the mass changes of the glacier’s melting season and accumulating season and the mass balance of different height of glacier from 3800 m to 3100 m. The results show that the mass balance of different height of glacier in 1999 are from -1471.2 mm w.e. to 103 mm w.e. respectively corresponded to 3800 m and 3300 m. Comparisons of the results of this study with the later time periods results of Koxkar glacier indicate an smaller mass loss. The paper demonstrates the feasibility of the presented method to obtain and analyze the mass balance of the mountain glacier.
Keyword: SAR observation; mountain glacier; mass balance; Koxkar glacier.
[Authors] [ Overview programme] [ Keywords]
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Paper 14 - Session title: Poster Session 1
Tuesday-78 - The Split-Band Interferometry Approach to determine the Phase Unwrapping Offset
Libert, Ludivine (1); Derauw, Dominique (1); d'Oreye, Nicolas (2); François, Kervyn (3); Christian, Barbier (1) 1: Centre Spatial de Liège, Belgium; 2: European Centre for Geodynamics and Seismology, Luxembourg; 3: Royal Museum for Central Africa, Belgium
Show abstract
Phase unwrapping is a key step of the Interferometric Synthetic Aperture Radar (InSAR) processing. Most phase unwrapping approaches attempt to retrieve the phase of a pixel with respect to the phase of its neighbouring pixels rather than the absolute phase. When decorrelation and discontinuities prevent from unwrapping the scene as a whole - for example when using branch cut algorithms or path-following methods - a 2πn-offset with n being an integer is introduced between regions which have been separately unwrapped. As a consequence, the phase cannot be compared between these regions. In this case, a reference point with known absolute phase is needed in each region to determine the phase offset between these discontinuous regions.
Recent developments [1, 2, 3] have shown that Split-Band Interferometry (SBInSAR) can take advantage of the large bandwidth of recent sensors (TerraSAR-X, Cosmo-SkyMed, Radarsat-2, Sentinel-1) to split it into sub-bands and compute several images with lower range resolution and slightly different carrier frequencies from a single acquisition. In the SBInSAR processing, the same spectral decomposition is applied to both master and slave acquisitions, yielding a stack of interferograms with different frequencies. Since the phase is supposed to change linearly with the carrier frequency, the last step of the processing consists in a pixel-by-pixel linear regression of the phase. The slope of this linear trend is proportional to the optical path difference and then enables to compute the absolute phase. The scatterers showing such a linear phase behaviour are referred to as « spectrally coherent » or « frequency-persistent scatterers » [4].
The potential of the method to retrieve absolute phase and therefore connect separately unwrapped areas without any ground-based measurement has been demonstrated in [2]. However, the phase accuracy was not satisfactory.
In the first part of this paper, we consider the phase obtained with SBInSAR processing and its standard deviation. We study the behaviour of the error on this split-band phase as a function of the parameters of the spectral decomposition (bandwidth, number of sub-bands, frequency shift) [3]. In order to accurately determine the 2πn-discrepancy between regions, the phase must be known with a precision better than a cycle. Given the requirement on the split-band phase accuracy, we define an upper bound on the phase variance in the stack of interferograms.
In the second part of this paper, we propose a statistical approach combining InSAR and SBInSAR to solve for the phase unwrapping offset between regions. Several criteria are investigated to select the frequency-persistent scatterers : spectral coherence, multi-frequency phase error, standard deviations on the intercept and the slope of the linear regression, linear correlation coefficient, goodness-of-fit and phase variance. Given the pixels selected with the estimators, the most probable offset is estimated to be the correct one.
The statistical approach is tested and validated on TerraSAR-X images for two study cases : the first case focuses on Splotlight High Resolution acquisitions on the Copahue volcano at the Chile-Argentina border. In this case, the images are acquired using a 300 MHz-chirp and, as can be expected, the results regarding the phase accuracy are satisfactory. For the second case, we use Strip-Map acquisitions on the Nyamuragira volcano (Democratic Republic of Congo) having a bandwidth of 150 MHz. Even though the bandwidth is decreased of a factor 2, we are able to compute the right phase offset with sufficient confidence.
This work was carried out in the frame of the MUZUBI project financed by Belgian Science Policy Contract NR SR/00/324.
REFERENCES:
[1] Bovenga, F., Giacovazzo, V. M., Refice, A., Veneziani, N. and Vitulli, R. (2009). Multi-Chromatic Analysis of InSAR data: validation and potential, Proceedings of FRINGE 2009, Frascati, Italy, 30 November-04 December 2009.
[2] De Rauw, D., Kervyn, F., d'Oreye, N., Albino, F., and Barbier, C. (2015). Split-Band Interferometric SAR Processing Using TanDEM-X Data, Proceedings of FRINGE’15: Advances in the Science and Applications of SAR Interferometry and Sentinel-1 InSAR Workshop, Frascati, Italy, 23-27 March 2015, Ouwehand L., Ed., ESA Publication SP-731. doi:10.5270/Fringe2015.20
[3] Veneziani, N., Bovenga, F. and Refice, A. (2003). A wide-band approach to absolute phase retrieval in SAR interferometry, Multidimensional Systems and Signal Processing, 14, 183-205. doi:10.1023/A:1022281310882
[4] Bovenga, F., Derauw, D., Rana, F.M., Barbier, C., Refice, A., Veneziani, N., Vitulli, R. (2014). Multi-Chromatic Analysis of SAR Images for Coherent Target Detection, Remote Sens., 6, 8822-8843. doi:10.3390/rs6098822
[Authors] [ Overview programme] [ Keywords]
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Paper 31 - Session title: Poster Session 1
Tuesday-50 - A Fine crustal Deformation Field For The Haiyuan Fault system from InSAR and GPS
Song, Xiaogang (1); Shan, Xinjian (1); Jiang, Yu (1,2); Qu, Chunyan (1); Zhang, Guohong (1) 1: State Key Laboratory of Earthquake Dynamics, Institute of Geology, Chinese Earthquake Administration, China, People's Republic of; 2: Dept. of Surveying and mapping Engineering, China University of Petroleum (East China)
Show abstract
The Haiyuan fault system is a major active tectonic feature in the northeastern margin of the Tibetan Plateau connecting the seismically active Qilian Shan in the west and the tectonically active Liupan Shan in the east, the latter abutting the relatively stable Ordos block. It is dominated by left-lateral strike slip faulting, which probably began in the late Pliocene or early Pleistocene, followed by late-stage folding and thrust faulting (Burchfiel et al., 1991). At its eastern end, left lateral slip on the N65°W striking Haiyuan fault zone has been transferred into shortening on the generally north trending structures in the Liupan Shan. Three arcuate zones of both strike-slip and thrust faults with associated ramp anticlines, lie about 40–170 km north and northeast of the Haiyuan fault zone. From south to north, the individual structures that comprise this arcuate system are the Tianjin Shan-Mibo Shan, Yanton Shan, and Niushou Shan-Daluo Shan fault zones. Tectonic activity within these areas is generally mild in comparison with that in the Haiyuan structural zone (Zhang et al., 1990).
A fine surface deformation velocity field is needed to provide an important constraint on geodynamic models of tectonic deformation as well as the assessment of earthquake hazard. Long-term GPS observations, spanning the 2009-2015 period, are processed to re-estimate a horizontal GPS velocity field covering the northeastern margin of the Tibetan Plateau. Interferometric synthetic aperture radar (InSAR) data from Envisat ASAR, spanning the 2003-2010 period, are used to measure interseismic strain accumulation across the whole Haiyuan fault system. In order to mitigate the atmospheric contamination in the interferograms, we use the atmospheric delay estimated from MERIS and ECMWF data. Mean line-of-sight (LOS) ratemaps are computed by stacking atmospheric-corrected and orbital-corrected interferograms from 6 interferometric descending tracks and 2 ascending tracks. The ratemaps from one track with different atmospheric-corrected results or two parallel, partially overlapping tracks, show a similar pattern of left-lateral motion across the fault, which demonstrates the MERIS and ECMWF atmospheric correction works satisfactorily for small stain measurement of this region, even with a limited number of interferograms. The velocity profiles show a distinct tectonic signal across the Haiyuan fault system. A strong change (2-3 mm/a) in line-of-sight (LOS) deformation rate across the fault can be seen along the whole fault except the Laohushan segment with a sharp gradient in a few kms wide region, and is qualitatively consistent with the left-lateral slip GPS velocities within the errors of the two measurements. There is no clear gradient in displacement rate related to tectonic signal on other fault.
To producing a high-resolution velocity and strain fields for this fault zone, we discretize our study area into an irregular grid based on the location of the faults firstly, then the InSAR and GPS data are inverted jointly to estimate a fine crustal deformation velocity field and a strain rate field. Strain accumulation is strongly localised on the Haiyuan fault system. The velocity and strain rate fields from joint inversion of InSAR and GPS and from GPS only are different, and the former shows strain localised on the transferring zone between the striking-slip Haiyuan Fault and thrusting Liupan shan Fault. This is likely due to the relatively high density of InSAR measurements in this region.
References
Burchfiel, B., P. Zhang, Y.Wang, W. Zhang, F. Song, Q. Deng, P. Molnar, and L. Royden, Geology of the Haiyuan fault zone, Ningxia-Hui Autonomous Region, China, and its relation to the evolution of the northeastern margin of the Tibetan Plateau, Tectonics, 10 (6), 1091–1110, 1991.
Zhang, P., B. Burchfiel, P. Molnar, W. Zhang, D. Jiao, Q. Deng, Y. Wang, L. Royden, and F. Song, Late Cenozoic tectonic evolution of the Ningxia-Hui autonomous region, China, Geological Society of America Bulletin, 102 (11), 1484–1498, 1990.
[Authors] [ Overview programme] [ Keywords]
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Paper 32 - Session title: Poster Session 1
Tuesday-13 - Coseismic deformation of the 2016 South Taiwan Mw6.3 earthquake from InSAR and source slip inversion
Qu, Chunyan; Shan, Xinjian; Zhang, Guohong; Song, Xiaogang Institute of Geology, China Earthquake Administration, China, People's Republic of
Show abstract
An earthquake of Mw6.3 occurred in southern Taiwan on 6 February 2016. We
used D-InSAR technology and Sentinel-1A/IW radar satellite data to estimate the
coseismic deformation of this event. From the ascending path, a 45km-sized
circle-like uplift area is present 20km northwest of the epicenter, with
largest LOS displacement 12cm. While from descending path, InSAR analysis gave
a pattern of uplift in the west and subsidence in the east, with maximum values
8.0cm and 6.0cm, respectively. The analysis of aftershock time series, and
distributions of their magnitudes and depths, coupling with InSAR deformation,
suggests that the causative fault is a NW-trending thrust with left slip, which
resulted in uplift in the frontal edge and subsidence in the rear edge during
its westward motion as a whole. The NS-distributed aftershocks might be caused
by a shallow fault induced by the mainshock rather than the mainshock rupture
itself. Based on InSAR deformation and GPS observations, we have conducted
inversion of fault slip in separate and joint manners. The four kinds of
inversion results consistently show a slip concentrating area northwest of the
epicenter, with largest values 0.35-0.56m confined to 6-15km depths. The joint
inversion using ascending/descending path InSAR and GPS data yielded maximum
slip 0.44m, between those of separate inversion results. The moment magnitude
for the 2016 Taiwan event from joint inversion is Mw6.25, well consistent with
Mw6.2-6.3 from USGS.
[Authors] [ Overview programme] [ Keywords]
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Paper 33 - Session title: Poster Session 1
Tuesday-2 - INSAR tropospheric correction combining GNSS data and a global atmospheric model
Simonetto, Elisabeth (1); Durand, Frédéric (1); Dubreuil, Vincent (1); Morel, Laurent (1); Nicolas-Duroy, Joëlle (1); Merrien-Soukatchoff, Véronique (1); Froger, Jean-Luc (2) 1: CNAM/GeF, France; 2: LMV, France
Show abstract
This work deals with the tropospheric phase screen (APS) estimation using GNSS measurements and global atmospheric models (ERA-Interim) useful for an interferogram correction.
After the assessment of the atmosphere parameters from the GNSS measurements at several ground receivers, the modelling of the atmospheric phase for INSAR is well known, including the directional effects and interpolation matter. However, several factors influence this estimation and we are interested in assessing the reliability of this approach.
A first work has shown that the APS estimation is influenced by the GNSS receiver network over the study area and the ZTD map interpolation method. Here, we go further by comparing the INSAR deformation measurements before and after the GNSS-based tropospheric correction and the GNSS displacement measurements.
Besides, we propose the analysis of the spatial correlation of the ZHD and ZWD values derived from GNSS. This analysis allows us to propose an adapted method for the estimation of the APS which is based on a global atmospheric model and GNSS tropospheric measurements.
Experiments are performed using SAR data and GNSS measurements acquired over the Piton de la Fournaise in France. We use several softwares (DORIS, TRAIN, …), GMT and Matlab scripts.
[Authors] [ Overview programme] [ Keywords]
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Paper 34 - Session title: Poster Session 1
Tuesday-51 - Rupture Model Of The 2015 M7.2 Sarez, Central Pamir, Earthquake And The Importance Of Strike-Slip Faulting In The Pamir Interior
Metzger, Sabrina (1); Schurr, Bernd (1); Ratschbacher, Lothar (4); Schöne, Tilo (1); Zhang, Yong (2); Kufner, Sofia-Katherina (1); Sudhaus, Henriette (3) 1: German Research Centre for Geosciences, Potsdam, Germany; 2: School of Earth and Space Sciences, Peking University, Beijing, China; 3: Christian-Albrechts-University, Kiel, Germany; 4: Technical University Freiberg, Freiberg, Germany
Show abstract
The Pamir mountain range, located in the Northwest of the India-Asia collision zone, accommodates approximately one third of the northward advance of the Indian continent at this longitude (i.e. ~34 mm/yr) mostly by shortening at its northern thrust system. Geodetic and seismic data sets reveal here a narrow zone of high deformation and M7+ earthquakes of mostly thrust type with some dextral strike-slip faulting observed, too. The Pamir interior shows sinistral strike-slip and normal faulting indicating north-south compression and east-west extension. In this tectonic setting the two largest instrumentally recorded earthquakes, the M7+ 1911 and 2015 earthquake events in the central Pamir occurred with left-lateral shear along a NE-SW rupture plane.
We present the co-seismic deformation field of the 2015 earthquake observed by Radar satellite interferometry (InSAR), SAR amplitude offsets and Global Positioning System (GPS). The InSAR and offset results reveal that the earthquake created a 50 km long surface rupture with maximum left-lateral offsets of more than two meters on a yet unmapped fault trace of the Sarez Karakul Fault System (SKFS). Surprisingly, field observations taken nine months after the event reveiled no single, clear surface offset, but rather a diffuse deformation zone and corridors of en-echelon shear ruptures, extensional crack, pressure ridges and sap ponds.
We derive a distributed slip-model including a thorough model parameter uncertainty study. Using a two-step approach to first find the optimal rupture geometry and then invert for slip on discrete patches, we show that a data-driven patch resolution produces yields a better representation of the near-surface slip and an increased slip parameter precision than a uniform patch approach without increasing the number of parameters and thus, calculation time. Our best-fit model yields a sub-vertical fault plane with a strike of N39.5 degrees and a rupture area of ~80 x 40 km2 with a maximum slip of 2 meters in the upper 10 km of the crust near the surface rupture.
The 1911 and 2015 earthquakes demonstrate the importance of sinistral strike-slip faulting on the SKFS, contributing both to shear between the western and eastern Pamir and extrusion of the western Pamir into the Tajik basin.
[Authors] [ Overview programme] [ Keywords]
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Paper 37 - Session title: Poster Session 1
Tuesday-16 - Surface Creep along the 1999 Izmit Earthquake's Rupture (Turkey ) from InSAR and GPS
Aslan, Gokhan (1,2); Cakir, Ziyadin (2); Lasserre, Cecile (1); Dogan, Ugur (3); Cetin, Seda (3); Renard, François (1); Ergintav, Semih (4) 1: ISTerre, CNRS, Université Grenoble-Alpes, Grenoble, France; 2: Department of Geological Engineering, ITU, Istanbul, Turkey; 3: Yıldız Technical University, Department of Geomatic Engineering, Istanbul, Turkey; 4: Boğaziçi University, Department of Geodesy, Kandilli Observatory and Earthquake Research Institute, Istanbul, Turkey
Show abstract
Previous studies based on InSAR and GPS observations have shown that the Izmit-Akyazı segment of the North Anatolian Fault (NAF) began slipping aseismically following the August 17, 1999 Izmit earthquake and continues for more than 13 years. To monitor this long-lasting afterslip, InSAR time series are computed based on a small baseline subset (SBAS) and Stanford Method for Persistent Scatterers (StaMPS) PS-InSAR approaches, using 32 TerraSAR-X radar images acquired between 2011 and 2015 from Supersites Istanbul archive provided by the German Aerospace Center, DLR (project HAZ2584_Marmara). The results show that the Izmit fault still creeps, but in an episodic manner. Two creep events seems to have occurred in the beginning and at the end of 2013, each with an offset of ~20 mm between Izmit and Lake Sapanca. Campaign GPS measurements on a recently established network with 35 benchmarks and LIDAR measurements on three sites confirm the ongoing aseismic activity along the fault.
The same approach has been applied to TerraSAR-X radar images acquired between 2011 and 2015 along another creeping section of NAF near Ismetpasa. The results reveal that the surface slip might be episodic as well with creep bursts alternating with periods of no slip.
[Authors] [ Overview programme] [ Keywords]
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Paper 45 - Session title: Poster Session 1
Tuesday-17 - Space geodetic observations and modelling of Jan. 21, 2016 Mw 5.9 Menyuan earthquake: Implications for characteristics of seismogenetic tectonic motion
Li, Yongsheng; Zhang, Jingfa; Jiang, Wenliang Institute of Crustal Dynamics, China Earthquake Administration, China, People's Republic of
Show abstract
Determining the relationship between crustal movement and faulting in thrust belts is essential for understanding the growth of geological structures and addressing proposed models of potential earthquake hazard. A Mw 5.9 earthquake occurred on Jan. 21, 2016 in Menyuan, NE Qinghai Tibetan plateau. In order to find out the seismogenic structure of both earthquakes and figure out relations among the earthquakes and the Lenglongling fault zone (LLLFZ), co-seismic deformation map of the InSAR is constructed by Sentinel-1A data. Moreover, the geological map, remote sensing images, aftershock relocation and GPS data are combined in the analysis.The results indicate that the reverse slip of the 2016 earthquake is distributed on a southwest dipping shovel-shaped fault segment. The main shock rupture initiated at the deeper part of the fault plane.
Fault behaviors of both earthquakes in 1986 and 2016 are also quite different from the pure left-lateral strike-slip of the LLLFZ. The focal mechanism of the 2016 earthquake mainly presents the extrusion stress, while the 1986 earthquake present the tension stress, both of which also behave slight of strike-slip motion. Both earthquakes occurred at the two ends of the secondary fault. Jointing analysis with the 1986 earthquake reveals an intense connection among these aftershocks and tectonic deformation of the Lenglongling faults. Under the shearing influence, the normal component is formed at the releasing bend of the western end of secondary fault for the left-order alignment of the fault zone, while thrust component is formed at the restraining bend of the east end for the right-order alignment of the fault zone. Earthquake activity and tectonic deformation of the LLLFZ play important parts in the Qilian-Haiyuan tectonic zone, as well as in the NE Tibetan plateau, which are results of collisions among the north Eursian-Asian plate, the east Pacific plate and the southwest Indian plate from three different directions. The Menyuan earthquake makes it very important to reevaluate the earthquake risk of the Lenglongling area.
[Authors] [ Overview programme] [ Keywords]
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Paper 50 - Session title: Poster Session 1
Tuesday-91 - A Novel Method for Noise Equivalent Sigma Nought Estimation
Leanza, Antonio (1); Monti Guarnieri, Andrea (1); Recchia, Andrea (2); Giudici, Davide (2) 1: Politecnico di Milano, Italy; 2: Aresys s.r.l., Italy
Show abstract
Noise Equivalent Sigma Nought (NESZ) is a radiometric parameter that measures the sensitivity of a given Synthetic Aperture Radar (SAR), defined as [1]. It is usually calculated by energetic consideration on the basis of the geometrical and electrical system parameters [2]. The theoretical value is usually assessed by in-flight measurements of noise spatial density over signal-free regions, typically windless water areas or shadow regions.
In this paper, we propose a novel single baseline interferometric method to perform NESZ estimation. The key aspect is given by the relationship between the received noise contribute and the corresponding target decorrelation. In fact, the coherence of a focused target is upper-bounded by a value that depends on the ratio between backscatter and the NESZ of the system.
This is shown in the coherence-backscatter histogram (figure 1 in the attached file). The idea is to exploit very long strips over a highly coherent scene, typically a desert, and find for each value of backscatter, those patches that mostly coherent. These edge points (shown are red dots) are used to fit the theoretical coherence versus SNR curve (see expression (1) in the attached file)
where γ0 is a parameter modelling the asymptotic scene coherence. The fit is performed for different range bins (then look angles) by providing a range-variant estimate of NESZ.
The effect of other decorrelation sources can be modelled according the expression (2) in the attached file. The first two components have been just discussed.
Common band and spectral shift are quite small in Sentinel-1, and they are further reduced in processing, similary for the coregistration. The DTAR acts like an incorrelated thermal noise, and it is either included in the estimation, or can be removed basing on the antenna model and the average backscatter. Notice that ambiguities affect much more the estimate based on dark areas, like shallow water. As for turbulence and surface roughness, the impact can be minimzed by exploiting small windows, that is allowed by the high coherence of the scene. Finally, the model is very robust in minimizing the impact of all those decorrelation source that are not following the curve (1), that happens in most cases.
The method has been applied to Sentinel-1A data and employed during Sentinel-1B commissioning phase. For both the sensors, the selected target area was “Salar de Uyuni”, a salt desert in the south of Bolivia. The results will be shown in the paper for several observation couples and for the two SAR systems, compared with the theoretical curves given by the model
REFERENCES
[1] http://earth.esa.int/handbooks/asar/CNTR5-2.html
[2] D. Calabrese, R. Episcopo, "Derivation of the SAR Noise Equivalent Sigma Nought," EUSAR 2014; 10th European Conference on Synthetic Aperture Radar, Berlin, Germany, 2014, pp. 1-4
[3] D. Just, R. Bamler, "Phase statistics of interferograms with applications to synthetic aperture radar," Applied Optics Vol.33, Issue 20, 4361-4368 (1994).
[Authors] [ Overview programme] [ Keywords]
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Paper 52 - Session title: Poster Session 1
Tuesday-141 - Visualizing All Sentinel-1 Data Through An Interactive Web-Tool
McDougall, Alistair University of Leeds, United Kingdom
Show abstract
With the ever increasing volume of data that the Sentinel constellation is generating, it is essential to have a system to visualise the valuable information contained within. Typically small spatial regions are studied separately, which produce detailed static figures over the targeted area of interest, but the source data provides detailed information about the entire globe. Therefore, we want to be able to see and interact with the entire global data set. We have developed a web-based tool that allows a user to move and zoom around the entire globe selecting each individual data point to view its full history of details that have been processed from the Sentinel-1 mission. Using a collection of open-source software a system has been built to visualise global data sets, which is currently being used to display the output from the COMET LiCS project. Through visualising the LiCS outputs, our tool enables users to see global plate motion, as well as local area deformations from sources such as mining. This system has been designed with big data in mind, and has been configured to continually grow as the satellites collect more data. With the underlying data continually updating, using a web-interface ensures that the user will always see the most up to date data available.
[Authors] [ Overview programme] [ Keywords]
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Paper 54 - Session title: Poster Session 1
Tuesday-145 - Earthquakes and Geo-hazard sites analysis using freeSAR web application
D'Aria, Davide; Riva, Davide; Maestri, Luca; Piantanida, Riccardo; Giudici, Davide; Recchia, Andrea ARESYS S.r.l. – Via Flumendosa 16, 20132 Milano - Italy
Show abstract
The European Space Agency (ESA), with the Sentinel-1 mission, has introduced an important change in the management of SAR data, freely opening the archives of the Level-0 and Level-1 products to the scientific community.
This opportunity has provided a huge amount of data to heterogeneous users, from SAR experts to volcanologists and geologists.
Free sharing of data paves the way also to sharing of results and inter-comparison of opinions among the different users.
An adequate set of processing tools, that give the opportunity to promptly process and inspect the results, provides support in this direction, ensuring that the data are processed on a common basis.
This paper is aimed at presenting a new service of SAR data processing for the SAR community, called FreeSAR.
FreeSAR is a web-based application aimed at supporting the scientific community through a simple, fast and user-friendly processing environment. It provides a complete processing chain, going from the L0 data up to the geocoded one, including tools for the generation of stacks of co-registered images, Persistent Scatterers analysis, and data rendering, everything through a common web-browser interface. FreeSAR makes SAR processing extremely simple. No complicated processing configuration are needed: just pick the inputs, run the task and enjoy the results.
The FreeSAR processing chain is composed by a set of tools here below listed:
• Focusing;
• Stacking, Co-Registration;
• InSAR & PS InSAR;
• Geocoding and multi-looking;
• Rendering.
In the paper, we put a specific attention to the assessment of deformations caused by Earthquakes and other geological events using Sentinel-1A/B data, putting particular attention to the events that hit Central Italy on 24 August 2016 and 30 October 2016.
[Authors] [ Overview programme] [ Keywords]
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Paper 55 - Session title: Poster Session 1
Tuesday-56 - The April 2016 M 7.8 Ecuador Earthquake: Estimation Of Surface Displacement And Modelling Of The Source Through Sentinel-1 SAR Data
Tessari, Giulia (1); Merryman Boncori, John Peter (2); Riccardi, Paolo (2); Pasquali, Paolo (2) 1: University of Padua, Italy; 2: Sarmap SA, Switzerland
Show abstract
On the 16th April 2016, a devastating earthquake affected the coastal Ecuador province of Manabí. The event, characterized by a 7.8 magnitude, provoked 661 deaths and left around 28000 people homeless. The tremor was triggered by the shallow thrust faulting on the plate boundary between the Nazca and Pacific plate, located offshore of the west coast of the northern Ecuador; the epicentre of the main shock was situated at 29 km SSE of Muisne, at a depth of 19.2 km and (USGS, 2016).
The availability of both ascending and descending Sentinel-1 SAR data, acquired before and after the considered earthquake, allowed to obtain two interferograms to analyse the surface effects due to the seismic event. In detail, two couples respectively of ascending and descending Sentinel data were analysed through Differential InSAR technique to estimate the surface displacement field induced by this event. Starting from the displacement map and the information about the fault location and the focal mechanism furnished by USGS, it was possible to recreate the model of the triggering source, the localization, geometrical parameters and the dislocation of the stresses along the fault adopting the Okada model (Okada 1985, 1992). Furthermore, the simulated source allowed to estimate the displacement induced by the fault itself. Therefore, a forward model allowed to reproduce the synthetic fringes produced by the event and subtract these estimated fringes from the observed interferogram, to obtain an interferogram where the residual fringes are due to the effects of other phenomena activated from the earthquake, such as landslides, building damages and collapse of bridges and infrastructures in general. The localisation of such catastrophic effects was confirmed by the technical report published by GEER-ATC (2016) and EERI (2016) which censes the damages through specific field observations. An additional attempt, to identify the earthquake effects and the surface deformations induced by this event, considered the amplitude tracking technique, searching for the amplitude offset over the area hit by the April 2016 earthquake.
EERI, Earthquake Engineering Research Institute, 2016. EERI Earthquake Reconnaissance Team Report: M7.8 Muisne, Ecuador Earthquake on April 16, 2016. ISBN: 978-1-932884-69-2
GEER-ATC, Earthquake reconnaissance, April 16th 2016, Muisne, Ecuador, version 1, October 14th 2016.
Okada Y., 1985. Surface deformation due to shear and tensile faults in a half-space, Bulletin of the Seismological Society of America, 75, pp. 1135 – 1154.
Okada Y., 1992. Internal deformation due to shear and tensile faults in a half-space. Bulletin of the Seismological Society of America, 82 (2), pp. 1018 – 1040.
USGS: United States Geological Survey USGS. “M7.8 - 29km SSE of Muisne, Ecuador." USGS. Accessed.June 12, 2016. http://earthquake.usgs.gov/earthquakes/eventpage/us20005j32#executive
[Authors] [ Overview programme] [ Keywords]
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Paper 61 - Session title: Poster Session 1
Tuesday-60 - Monitoring condition and assessing damage in cultural heritage sites at risk with TerraSAR-X Staring Spotlight
Tapete, Deodato; Cigna, Francesca British Geological Survey, Natural Environment Research Council, United Kingdom
Show abstract
Since mid-2014 the project TSX-New-Modes-2013 LAN2377 (Principal Investigator: Dr D. Tapete) has aimed to demonstrate the scientific potential of the new TerraSAR-X Staring Spotlight mode (ST) to support cutting-edge research and real-world applications of damage assessment, looting monitoring and prospection of archaeological features in semi-arid environments, with test sites in Syria. In light of the unprecedented imaging capability with azimuth resolution of up to 0.24 m, ST has been tested to detect meter to sub-meter sized land surface features due to actions of illegal excavations in archaeological sites – namely ‘archaeological looting’. For the first time, building upon the methodology by Tapete et al. (2013), a novel conceptual model has been proposed to explain how ‘looting marks’ look like in SAR images and a quantitative method of amplitude change detection has been developed to measure rates of occurrence based on SAR that might complement existing assessment methods using very high resolution optical imagery (Tapete et al., 2016). Since October 2014 an experimental campaign is being carried out over the Hellenistic site of Apamea (inscribed on the UNESCO Tentative List) and thousands of looting holes have been observed every two months, by distinguishing those due to new looting and those as an alteration (e.g. filling) of pre-existing holes. To follow on from this initial experimental phase, the project is now looking at applying this methodology to the Syrian World Heritage Sites of Aleppo and Bosra and other sites across the country where evidence of archaeological looting has been found and documented. The nearly simultaneous analysis of the above Syrian sites is allowing the project: (i) to acquire a consistent image dataset to understand patterns and trends of looting in Syria and (ii) evaluate whether the ST technology developed by DLR can be used for such type of assessment to provide updated and detailed knowledge basis to national and international organizations of cultural heritage protection.
References
Tapete, D., Cigna, F., Masini, N. & Lasaponara, R. (2013) Prospection and Monitoring of the Archaeological Heritage of Nasca, Peru, with ENVISAT ASAR. Archaeological Prospection, 20(2), 133–147. doi: 10.1002/arp.1449
Tapete, D., Cigna, F. & Donoghue, D.N.M. (2016) ‘Looting marks’ in space-borne SAR imagery: Measuring rates of archaeological looting in Apamea (Syria) with TerraSAR-X Staring Spotlight. Remote Sensing of Environment 178: 42–58. doi:10.1016/j.rse.2016.02.055
[Authors] [ Overview programme] [ Keywords]
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Paper 65 - Session title: Poster Session 1
Tuesday-18 - InSAR Monitoring of Small Different Deformation Between the Two Sides of Urban Active Fault
Zhang, Ling; Liu, Bin; Ge, Daqing; Gan, Fuping China Aero Geophysical Surveying & Remote Sensing Center for Land and Resources, China, People's Republic of
Show abstract
InSAR (Synthetic Aperture Radar Interferometry) , with the advantages of high efficiency, wide coverage and low cost, is a key technology for surface deformation survey in recent years. In this study, the small differential deformation of the main 3 NNE active faults in Tangshan urban area is monitored. Two kinds of radar data are used with the coherent target analysis method. One data is the Wide mode of Radarsat-2 with 30m spatial resolution while the other one is the Strip mode of TerraSAR-X with 3m spatial resolution. According to the deformation velocity of the coherent points, a deformation profile line nearly orthogonal to fractures and a fitting line of coherent points group in buffer area are analyzed. The results show:
(1) The fitting line of point set resulted from RADARSAT-2 medium resolution data can be more clearly show the tiny difference deformation between the two sides of the active faults, which shows that InSAR technology can be used as an auxiliary monitoring means of active faults.
(2) The deformation difference is very small and easily to be contaminated by other errors, such as atmospheric errors, track residuals, etc..
(3) The deformation difference of Tandshan-Guye fault is more obvious than Douhe and Weishan-Changshan faults, which is 2mm/a in 2012 to 2014.
(4) The deformation results is effected by many factors. The faults slip rate is 2-5mm/a in mainland, which leads the monitoring need a large spatial and temporal space. On the contrary, the coherence of SAR image decreases with a longtime, and the 3 faults are close. In city region, human activities, ground covers influence are resulting difficulty in distinguishing faults deformation. So, InSAR measuring results cannot directly determine the deformation of the fault activity, should be jointed other sources to monitoring the faults activities.
[Authors] [ Overview programme] [ Keywords]
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Paper 67 - Session title: Poster Session 1
Tuesday-54 - Postseismic deformation of the 2105 Mw 6.5 Pishan, Xijiang earthquake from Sentinel-1 data
Wen, Yangmao (1,2,3); Xu, Caijun (1,2,3); Liu, Yang (1,2,3); Jiang, Guoyan (3) 1: School of Geodesy and Geomatics,Wuhan University, China; 2: Key Laboratory of Geospace Environment and Geodesy of the Ministry of Education, Wuhan University, China; 3: Collaborative Innovation Center of Geospatial Technology, Wuhan University, China
Show abstract
On 3 July 2015, a Mw 6.5 earthquake struck Pishan in Xinjiang, western China, which is located in the boundary between the southwestern Tarim Basin and the northwestern Tibetan Plateau. The event caused at least four deaths, 48 injuries and hundreds of building collapses. In this study, a multitemporal Interferometric SAR (InSAR) time series technique is used to map the postseismic motion following the Pishan event. SAR data from the ascending and descending Sentinel-1 satellite Terrain Observation with Progressive Scans (TOPS) mode are used to derive the displacement time series within 1 year after the event. The results show that the displacement in radar line of sight is about 2 cm around the epicenter during the period and decays with time. The observed surface displacements are consistent with afterslip on the shallow part of the coseismic fault plane, which indicates that the unreleased accumulated strain energy during the event is released by the afterslip.
[Authors] [ Overview programme] [ Keywords]
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Paper 68 - Session title: Poster Session 1
Tuesday-19 - The mechanism of partial rupture of a locked megathrust: The role of fault morphology
Qiu, Qiang (1,2,3); Hill, Emma (2,3); Barbot, Sylvain (2,3); Hubbard, Judith (2,3); Feng, Wanpeng (4); Lindsey, Eric (2,5); Feng, Lujia (2); Dai, Keren (6); Samsonov, Sergey (4); Tapponnier, Paul (2,3) 1: School of Earth and Environment University of Leeds, Singapore; 2: Earth Observatory of Singapore, Nanyang Technological University, Singapore; 3: Asian School of the Environment, Nanyang Technological University, Singapore; 4: Canada Centre for Mapping and Earth Observation, Natural Resources Canada, 560 Rochester Street, Ottawa, ON K1A 0E4 Canada; 5: Institute for Geophysics and Planetary Physics, University of California, San Diego, USA; 6: Dept. of Remote Sensing and Geospatial Information Engineering, Southwest Jiaotong University, Chengdu, China
Show abstract
Assessment of seismic hazard relies on estimates of how large an area of a tectonic fault could potentially rupture in a single earthquake. Vital information for these forecasts includes which areas of a fault are locked and how the fault is segmented. Much research has focused on exploring downdip limits to fault rupture from chemical and thermal boundaries, and along-strike barriers from subducted structural features, yet we regularly see only partial rupture of fully
locked fault patches that could have ruptured as a whole in a larger earthquake. Here we draw insight into this conundrum from the 25 April 2015 Mw 7.8 Gorkha (Nepal) earthquake. We invert geodetic data with a structural model of the Main Himalayan thrust in the region of Kathmandu, Nepal, showing that this event was generated by rupture of a décollement bounded on all sides by more steeply dipping ramps. The morphological bounds explain why the event ruptured only a small piece of a large fully locked seismic gap. We then use dynamic earthquake cycle modeling on the same fault geometry to reveal that such events are predicted by the physics. Depending on the earthquake history and the details of rupture dynamics, however, great earthquakes that rupture the entire seismogenic zone are also possible. These insights from Nepal should be applicable to understanding bounds on earthquake size on megathrusts worldwide.
[Authors] [ Overview programme] [ Keywords]
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Paper 69 - Session title: Poster Session 1
Tuesday-143 - Subsidence in the Perth Basin: first results from Sentinel-1A InSAR over Australia
Parker, Amy Laura; Filmer, Mick S; Featherstone, Will E Curtin University, Australia
Show abstract
Groundwater abstracted from subsurface aquifers meets ~40% of the water requirements in Perth, Australia. However, groundwater levels have reduced in recent decades as the population increases and rainfall decreases. The link between groundwater abstraction and subsidence is well documented, and past ground-based geodetic measurements in the Perth Basin attribute small-magnitude subsidence (<7 mm/yr), to groundwater abstraction. Ground-based surveys are limited to discrete points or traverses across parts of the metropolitan area and therefore do not reveal the full extent of deformation. To overcome this, we perform the first-ever application of Sentinel-1A InSAR data to Australia, investigating a much larger region (~85 km x 150 km). Between August 2015 and May 2016, Sentinel-1A data were acquired over Perth in an ascending orbit at 24 day intervals. Despite this short observation-period, verification of Sentinel-1A with independent TerraSAR-X provides new insights into the deformation field of the Perth Basin. We identify broad (>10 km wide) areas of subsidence at rates less than -10 mm/yr, plus subsidence of greater than -10 mm/yr over smaller areas (<5 km wide) that is largely coincident with wetlands. Time-series analysis shows that displacements observed at wetlands are temporally correlated with changes in groundwater levels in the superficial aquifer. Overall the LoS displacements recorded by each satellite are in close agreement, demonstrating the ability of Sentinel-1A to detect small-magnitude deformation over different spatial scales (from 2 km to 10s km), even over short time-periods (<1 year). Since the commissioning of Sentinel-1B, the Perth Basin is expected to be consistently imaged from a descending orbit at 12 day intervals. These observations will provide a longer InSAR time-series, which is required to determine whether the measured displacements are representative of long-term deformation or (more likely) seasonal variations
[Authors] [ Overview programme] [ Keywords]
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Paper 72 - Session title: Poster Session 1
Tuesday-117 - Using TanDEM-X observations for extracting glacier and sea-ice topographies
Hong, Sang-Hoon (1,3); Wdowinski, Shimon (2); Amelung, Falk (3); Won, Joong-Sun (4); Kim, Hyun-Cheol (1) 1: Korea Polar Research Institute, Korea, Republic of (South Korea); 2: Florida International University, Miami, FL, U.S.A.; 3: University of Miami, Miami, FL, U.S.A.; 4: Yonsei University, Korea, Republic of (South Korea)
Show abstract
Space-based Synthetic Aperture Radar interferometry (InSAR) applications have been widely used for monitoring the cryosphere over past decades. Due to temporal decorrelation, interferometric coherence often degrades severely on fast moving glaciers and sea-ice. In addition, higher sensitivity ambiguity by large baseline configurations, which are needed for extracting topographic information over low relief areas such as sea-ice surfaces. TanDEM-X observations, which overcome the temporal decorrelation due to its simulatanious measurements by its two sattelite constellation, has used short baseline of 150 m to 500 m which are sufficient for generating excellent DEM in most locations around the world. However, it is still difficult to estimate detail topographic characteristics over low slope sea-ice or glacier surfaces due to relatively less sensitive height ambiguity from small baselines.
In this study, we use the TanDEM-X large baseline formation following scientific phase timeline to generate high spatial and sensitive topographic elevation model for glaciers and sea-ice. We obtained seven TanDEM-X bistatic and pursuit monostatic mode observations of glaciers and sea-ice located in both Greeland and Antarctica. As expected, coherent interferometric phases (0.5 ~ 0.8) are well maintained over sea-ice and glaciers despite their fast movements, thanks to TanDEM-X simultanious measurements. The height ambiguity of the datasets are ranged from 7.1 ~ 9.7 m, which is very favourable for extracting topographic information in low relief region. Because of high sensitive ambiguity, we can extract detailed geomorphological features like surface roughness on sea-ice and glaciers. High resolution interferometric phase including topographic information is also useful for separating iceberg from sea-ice or open water. We also validated the TanDEM-X derived sea-ice topography by comapring it to the SAR/Interferoemtric Radar Altimeter observations acquired by CryoSat-2. Both observations show very good correlation with a few meters of offsets, which can be used for calibrating TanDEM-X topography. Routine TanDEM-X observations will be very useful for understanding better the dynamics of sea-ice and glacier movements.
[Authors] [ Overview programme] [ Keywords]
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Paper 73 - Session title: Poster Session 1
Tuesday-80 - Evaluation of space-based wetland InSAR observations with Sentinel-1 interferometric wide (IW) swath mode
Hong, Sang-Hoon (1,3); Wdowinski, Shimon (2) 1: Korea Polar Research Institute, Korea, Republic of (South Korea); 2: Florida International University, Miami, FL, U.S.A.; 3: University of Miami, Miami, FL, U.S.A.
Show abstract
Wetland Interferometric Synthetic Aperture Radar (InSAR) is a unique application of the InSAR technique, which detects water level changes in aquatic environments with emergent vegetation at high spatial resolution over wide areas [1-3]. In this study we evaluate the suitability of Sentinel-1 interferometric wide swath (IW) acquisition mode’s observations for the wetland InSAR application. We test Sentinel-1 observations in two study areas, which are the south Florida Everglades in the United States and the Cienaga Grande de Santa Marta (CGSM) in northern Colombia. The Everglades, which is a World Heritage Site, is the largest natural region of subtropical wilderness in the United States. The CGSM is vast wetland and upland area located along the Caribbean coast of Colombia. Both wetlands have been threatened by severe environmental stresses induced by anthropogenic activities, as agricultural development and urban expansion, as well as by natural causes, such as sea level rise and climate change. With the recognition of their ecological importance, various restoration plans have been authorized to preserve and restore these invaluable wetland ecosystems. Due to the vast extent and remoteness of these wetlands, monitoring their ecological and hydrological conditions are best conducted using remote sensing observations.
The Sentinel-1 satellites can acquire SAR data over a 250 km wide swath with 12 days repeat pass, which are very useful for detecting and monitoring small changes of the Earth’s surfaces. Because recently the Sentinel-1B has been launched successfully in orbit with phase continuity of the Sentinel-1A, only 6-day interferometric temporal baseline can be utilized for the wetland InSAR application. The satellite’s standard acquisition mode, wide swath IW, acquires data over a 250 km swath with a spatial resolution of about 5 m in range and 20 m in azimuth directions, thanks to the Terrain Observation by Progressive Scans (TOPS) technique. Such observations are very useful for monitoring hydrological condition over wetlands, which can vary daily due to rain events and/or surface flow. Moreover, the 6-day or 12-day repeat pass observations of Sentinel-1 provide a great advantage for maintaining higher interferometric coherence over wetlands, which their vegetated environment induces rapid temporal decorrelation.
Our preliminary results are based on interferometric pairs acquired over the Everglades between 2015/09/21 and 2016/11/14 and the CGSM from 2014/10/27 to 2016/11/15. We processed this pair using the Gamma software, which generates differential interferograms and eliminates topographic effects using a digital elevation model (DEM). We used 3 arc-seconds Shuttle Radar Topography Mission DEM for topographic phase removal. We also used multi-looking and phase filtering to enhance the signal to noise ratio.
The preliminary interferograms show an overall low gradient fringes over the CGSM wetlands, which are mainly covered with herbaceous vegetation. Because a man-made road across the wetland blocked a natural hydrologic environment between see and fresh water at the CGSM, ecological catastrophes were occurred [4-5]. This ecological disturbance caused the hyper saline conditions resulting in massive mortality of mangroves at the end of the 20th century. It is interesting to note that coherent phase is better maintained over dead or rehabilitated mangrove areas than over live mangrove areas. It might be resulted from that leafy and heavy mangrove forest prevents the radar signal from maintaining coherence. Because volume scattering in heavy vegetated area does not allow maintaining coherence over time. The low coherence indicates that the mangrove forest at CGSM is tall and massive, because small and intermediate height mangrove forests yield coherent phase, as we observed in the Everglades wetlands [6].
We will continue evaluating the Sentinel-1 IW interferograms with in-situ observations from water level stage stations. Furthermore, the planned frequent data acquisition of every repeat cycle (6 or 12 days) will provide us new understanding of the hydrological conditions and their changes over time at the entire wetland scale.
Index Terms – Sentinel-1, interferometric wide swath (IW) mode, wetland InSAR, Everglades, Cienaga Grande de Santa Marta (CGSM).
[1] Alsdorf, Douglas E., et al. "Interferometric radar measurements of water level changes on the Amazon flood plain." Nature 404.6774 (2000): 174-177.
[2] Wdowinski, Shimon, et al. "Space‐based measurements of sheet‐flow characteristics in the Everglades wetland, Florida." Geophysical Research Letters 31.15 (2004).
[3] Hong, Sang-Hoon, Shimon Wdowinski, and Sang-Wan Kim. "Evaluation of TerraSAR-X observations for wetland InSAR application." Geoscience and Remote Sensing, IEEE Transactions on 48.2 (2010): 864-873.
[4] Botero, Leonor, and Horst Salzwedel. "Rehabilitation of the Ciénaga Grande de Santa Marta, a mangrove-estuarine system in the Caribbean coast of Colombia." Ocean & Coastal Management 42.2 (1999): 243-256.
[5] Simard, Marc, et al. "A systematic method for 3D mapping of mangrove forests based on Shuttle Radar Topography Mission elevation data, ICEsat/GLAS waveforms and field data: Application to Ciénaga Grande de Santa Marta, Colombia." Remote Sensing of Environment 112.5 (2008): 2131-2144.
[6] Wdowinski, S., S-H. Hong, A. Mulcan, and B. Brisco, Remote sensing monitoring of tide propagation through coastal wetlands, Oceanography (2013): 26(3):64–69, DOI 10.5670/ oceanog.2013.46.
[7] Hong, S. -H., Wdowinski, S., & Kim, S. -W., Evaluation of TerraSAR-X observations for wetland InSAR application. IEEE Transactions on Geoscience and Remote Sensing (2010), 48, 864−873.
[Authors] [ Overview programme] [ Keywords]
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Paper 76 - Session title: Poster Session 1
Tuesday-113 - Strain of Landfast Sea Ice around Campbell Glacier Tongue in East Antarctica Revealed by InSAR
Han, Hyangsun (1); Lee, Hoonyol (2) 1: Korea Polar Research Institute, Korea, Republic of (South Korea); 2: Kangwon National University, Korea, Republic of (South Korea)
Show abstract
Landfast sea ice, called fast ice for short, is a type of sea ice that is attached to the coastline or ice shelves. Strain of fast ice is indicates its dynamics that has large influences on the variability of polynya, marine ecosystem and logistics for research stations near the coast. Therefore, it is important to accurately measure the strain of fast ice. Fast ice around Campbell Glacier Tongue (CGT) in Terra Nova Bay (TNB), East Antarctica experiences both glacial strain by the gravitational flow of CGT in the horizontal direction and tidal strain by sea surface tilt in the vertical direction. In this paper, we separated the glacial and tidal strain of fast ice around CGT from 20 one-day Interferometric Synthetic Aperture Radar (InSAR) images generated from a total of 70 COSMO-SkyMed SAR images obtained from December 2010 to January 2012. We assumed that the axial direction of glacial strain is perpendicular to the side of CGT while that of tidal strain is perpendicular to its hinge line, by analyzing ice flow of CGT, geometry of TNB and tidal bending characteristics of fast ice and CGT. The glacial strain represented that fast ice in the east and west of CGT experienced the deformation by shearing. The shearing deformation of the fast ice decreased as the distance from the edge of CGT increases. The one-day InSAR-derived glacial strains were little deviated from those estimated from 57 weekly (18 seven-days and 39 eight-days, respectively) InSAR images in which glacial strain of fast ice was observed dominantly due to cumulative flow of CGT and oscillating tide height. Magnitudes of the one-day InSAR-derived tidal strain of the fast ice were strongly correlated with those of the tide variation during the observations. Fast ice isolated from CGT by cracks and leads showed tidal strain only because glacial stress was not reachable. The tidal strain responding to tide variations estimated from the one-day InSAR images were very similar to those from double-differential InSAR (DDInSAR) images which were generated by differentiating two InSAR images containing similar glacial strain. The weekly InSAR and DDInSAR images confirmed that the glacial and tidal strain revealed from the one-day InSAR images are reasonable.
[Authors] [ Overview programme] [ Keywords]
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Paper 77 - Session title: Poster Session 1
Tuesday-133 - Mapping Three-Dimensional Time-Series Displacements of Datong Coal Mining Area, China, Using Ascending PALSAR Images
Yang, Zefa (1,2); Li, Zhiwei (1); Zhu, Jianjun (1) 1: Central South University, China; 2: RWTH Aachen University, Germany
Show abstract
It is essential to monitor mining-induced three-dimensional (3-D) time-series displacements, in order to assess mining-related geo-hazards and understand the dynamics of mining subsidence. However, due to the side-looking imaging geometry of current SAR sensors, the deformation provided by interferometric synthetic aperture radar (InSAR) is one-dimensional (1-D) (i.e., along the radial line-of-sight (LOS) direction). Therefore, only LOS time-series deformation can be monitored by conventional multi-temporal InSAR (MT-InSAR) techniques (e.g., persistent scatterers InSAR and small-baseline subset InSAR) when only a single geometry SAR data are available. Generally, the SAR dataset with at least three different imaging geometries are needed if the full 3-D time-series displacements are estimated using MT-InSAR techniques. Nevertheless, this is difficult to be met because of the limited number of available SAR sensors.
We present a method for mapping 3-D time-series displacements of coal mining areas using a single geometry SAR dataset in this paper. The horizontal motion and the gradient of vertical subsidence caused by underground extraction is usually proportional to each other. Hence, we first apply this proportional relationship to constrain to stabilize the under-determined system from 1-D InSAR LOS observations to 3-D displacements. Consequently, the multi-temporal observations of the vertical subsidence are obtained from the available InSAR pairs generated by the single geometry SAR acquisitions. Afterwards, an interferometric coherence-based weighted least square method is applied to estimate the time series of the mining-induced vertical subsidence from the SPI-derived multi-temporal observations. Having obtained the time-series vertical subsidence, the horizontal motions in the easting and northing directions are accordingly determined, on the basis of the proportional relationship between the horizontal displacement and the gradient of vertical subsidence in mining areas.
The proposed method was tested in the Datong Coal Mining Area, China, using seven ascending ALOS PALSAR data spanning from 1 July 2007 to 18 May 2008. The results show that the maximum 3-D displacements in this period reach up to 0.95, 0.11 and 0.34 m respectively, and the accuracies of the estimated 3-D time-series displacements are about 0.023, 0.009 and 0.014 m in the vertical, easting and northing directions, respectively.
[Authors] [ Overview programme] [ Keywords]
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Paper 80 - Session title: Poster Session 1
Tuesday-20 - Investigating ground instabilities in Sumatra and Java islands by integrating SAR Interferometry and GNSS
Bovenga, Fabio (1); Refice, Alberto (1); Belmonte, Antonella (1); Nutricato, Raffaele (2); Nitti, Davide Oscar (2); Chiaradia, Maria Teresa (2); Ganas, Athanassios (3); Manunta, Paolo (4); Elizar, Elizar (5); Bally, Philippe (6) 1: National Research Council, CNR-ISSIA, Italy; 2: Dip. di Fisica “M. Merlin”, University of Bari, Italy; 3: National Observatory of Athens (NOA), Athens, Greece; 4: Collaborative Space Ltd, Dundrum, Ireland; 5: Syiah Kuala University, Banda Aceh, Indonesia; 6: European Space Agency, ESA-ESRIN, Frascati, Italy
Show abstract
Indonesia is periodically affected by severe volcanic eruptions and earthquakes, which are geologically coupled to the convergence of the Australian tectonic plate beneath the Sunda Plate. SAR interferometry (InSAR) can be used to support studying and modeling of terrain movements such as tectonic motions associated with faults. Multi-temporal InSAR (MTI) techniques provide both mean displacement maps and displacement time series over selected, stable objects on the Earth surface. Nowadays, historical SAR data acquired in different bands and from several satellite missions are available, and the launch of Sentinel-1A/B guarantees data for the next future. The study of tectonic phenomena requires large-scale spatial analysis that poses challenges in MTI processing. A reliable modeling needs additional information coming e.g. from geodetic data, such as those provided by GNSS networks.
This work is aimed at performing an analysis of ground displacements over Indonesian sites through MTI techniques. Test sites have been selected according to the availability of archived SAR data, GNSS networks, and geological data. Based on the existence of i) onshore active faults, ii) undergoing deformation as from GPS data, iii) foreseen good interferometric coherence, iv) availability of SAR imagery, two stacks of COSMO-SkyMed data, both acquired in stripmap mode between 2011 and 2015 , have been selected, one on the capital Banda Aceh (descending geometry, mean incident angle of 32.2°) and a second one on the city of Yogyakarta (ascending geometry, mean incident angle of 29.3°). Geological maps of the Banda Aceh and Yogyakarta test sites are available, and several GNSS stations from the Continuously Operating Reference Stations (CORS) Indonesian network are found to be located in the areas of interest: 24 in Banda Aceh and 36 in Yogyakarta. For each station, horizontal velocity values and displacement time series are available.
Sentinel-1 data are also available, even though their number is quite limited (between 20 and 30) because of the reduced acquisition frequency. Nevertheless, Sentinel-1 acquisition geometries on the two test sites are complementary to those of the COSMO-SkyMed data, thus allowing in principle the combination of InSAR-based displacement maps derived from different viewing geometries. Both the SPINUA and the StaMPS algorithms have been used to process the data. The former is well suited for scarcely urbanized areas and high resolution local scale analysis, while the latter has been proven effective for studying both volcanic deformations and fault slips. This processing strategy also allows us to cross-validate MTI results.
Integration of Java and Aceh province observations from SAR satellites with ground-based GNSS observations has been attempted, with the aim of producing a uniform product, improving on the existing, low-resolution global strain rate map (http://gsrm.unavco.org/) derived from GNSS alone.
The work describes the MTI processing adopted, and the procedure developed to integrate the MTI deformation maps with the records derived from GNSS observations. The ground deformations undergoing on the area of interest are then modeled according to these integrated products.
ACKNOWLEDGMENTS
Work supported by ESA project titled “Integrating SAR interferometry and GNSS for studying tectonic processes in Indonesia” (contract 4000114611/15/F/MOS), ESA ITT AO/1-7864/14/F/MOS, Alcantara Study reference 14-P16 “Alcantara Study Enhanced Tectonic Characterization for Indonesia”. COSMO-SkyMed data are provided in the framework of the ESA CAT-1 Third Party Mission (TMP) proposal ID 33378.
[Authors] [ Overview programme] [ Keywords]
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Paper 87 - Session title: Poster Session 1
Tuesday-7 - Mitigation Of Atmospheric Phase Delay In SAR Interferrograms Of Norcia’s Earthquake
Nico, Giovanni (1); Conde, Vasco (2); Mateus, Pedro (2); Catalao, Joao (2); Tomé, Ricardo (2) 1: Consiglio Nazionale delle Ricerche (CNR), Istituto per le Applicazioni del Calcolo (IAC), Italy; 2: Universidade de Lisboa, Instituto Dom Luiz, Lisbon, Portugal
Show abstract
A sequence of earthquakes has hit the Centre Italy starting from August 2016 and still continuing up to now. The quakes have affected the regions of Lazio, Umbria and Marche with the destruction of small villages in the Apennines mountains. An in-situ inspection has registered relative displacements of the main faults in the area in the order of a few centimetres. Synthetic Aperture Radar (SAR) interferometry is already a mature technique to map such terrain displacements over large regions. In fact, starting from the very beginning many research group have made available to the general public maps of earthquake-induced terrain displacements using both X-band Cosmo-Sky-Med and C-band Sentinel-1 SAR images provided by the Italian and the European Space Agencies, respectively. In this work we study the problem of estimating the phase delay due to the propagation of SAR signal in neutral component of atmosphere. This delay is mainly related to temporal and spatial variations of water vapour spatial distribution in the atmosphere. This is an open issue in SAR interferometry and is of crucial importance when using only an interferogram and not a time series as in the case of earthquake when terrain displacements are measured by processing two SAR images, one before one after the seismic event.
In this work we show the SAR interferograms of the seismic event before and after the mitigation of atmospheric phase delay. The mitigation procedure is based on the use of the WRF model. The impact of assimilating estimates of atmospheric phase delay from in-situ measurements and spaceborne data into the WRF model is also investigated.
The earthquake of 31st of October 2016 has been chosen as a case study since it has the been the strongest one in the sequence of seismic events. Four couples of Sentinel-1 SAR images have been used to generate four independent coseismic interferograms, along both ascending and descending orbits. WRF data have been generated for each of the eight SAR images used to generate the four interferograms. Starting from the WRF output synthetic maps of atmospheric phase delay have been generated and used to mitigate the atmospheric phase delay effects in the four interferograms.
Since the four interferograms refer to the same seismic event it is expected that the corresponding geolocated terrain displacement patterns be in agreement each other if the displacement is purely vertical. However, differences are observed mainly due to the different propagation delays in atmosphere. A statistical analysis of terrain displacement patterns before and after mitigation of atmospheric propagation delays is carried out to quantify the performances of the mitigation procedure.
References
[1] G. Nico, R. Tomé, J. Catalão, and P. Miranda, “On the use of the WRF model to mitigate tropospheric phase delay effects in SAR interferograms,” IEEE Trans. Geosci. Remote Sens., vol. 49, no. 12, pp. 4970–4976, Dec. 2011.
[2] P. Mateus, G. Nico, J. Catalão, “Uncertainty assessment of the estimated Atmospheric delay obtained by a Numerical Weather Model (NMW).” IEEE Transactions on Geoscience and Remote Sensing, 53(12), doi:10.1109/TGRS.2015.2446758, 2015
[Authors] [ Overview programme] [ Keywords]
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Paper 89 - Session title: Poster Session 1
Tuesday-61 - Merging the Sentinels and Landsat to provide evidence base maps of green infrastructure in UK cities
Tapete, Deodato; Lee, Kathryn; Cigna, Francesca; Fleming, Claire; Cartwright, Clive British Geological Survey, Natural Environment Research Council, United Kingdom
Show abstract
In the last 15 years, Green Infrastructure (GI) defined as a network of multifunctional green spaces, urban, rural and water has increasingly got higher priority on the urban agenda. This reflects the international recognition of the key role of GI in strategic land use planning to deliver environmental and quality of life benefits (European Commission communication COM/2013/0249 on Europe’s Natural Capital; United Nations Sustainable Development Goals, 2015).
City councils in the UK frequently underpin their green space strategies using evidence base maps that show where there is environmental, social, economic and cultural potential for GI to deliver public benefits across their administrative boundaries. Although these maps are factual and based on inventoried green space, they may have the limitation of providing a static snapshot of the GI situation at a specified time. Therefore they do not necessarily capture the dynamic changes of GI within the urban footprint and, more importantly, along the rural-to-urban fringes where opportunities for urban development can manifest.
This paper presents how the freely accessible regular acquisitions from the European Space Agency (ESA) Sentinel satellites can be used, in conjunction with Landsat time series, to create, and keep updated, maps showing the spatial distribution of GI and their changes in land cover and land use as a result of urban development projects.
Sentinel-1 acquired in spring and autumn sessions in 2016 were classified by testing the different properties of the SAR images, including the dual polarization VV and VH, and their temporal changes. The GI polygons extracted from the supervised classification were then merged with those extracted from simultaneous Landsat acquisitions to produce a GI layer covering the West Midlands region. Matching the geometric accuracy of 50 m of the geological datasets held by the British Geological Survey, this evidence base map is suitable for geospatial analysis of GI against the properties of the subsurface. Where correlation is found with the properties of the ground, this is translated into geological opportunities for the installation of new GI or constraints for existing GI to function as intended.
The discussion will focus on how this type of product can be interrogated by city stakeholders and, alongside economic and social considerations, used to feed into the GI strategic planning at city scale level.
[Authors] [ Overview programme] [ Keywords]
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Paper 92 - Session title: Poster Session 1
Tuesday-87 - The combined analysis of PS and DS for monitoring airport stability with Sentinel-1A data
SHI, Guoqiang; LIN, Hui; MA, Peifeng; LIU, Yuzhou The Chinese University of Hong Kong, Hong Kong S.A.R. (China)
Show abstract
A comprehensive and detailed deformation monitoring for airports is sometimes difficult to achieve by traditional surveying technologies, as the continuous operating of airports significantly limits the deployment of instruments. Besides, critical areas with obvious subsidence and highly possible in reclaimed airports may be missed by the station-based measurements. For decades, Interferometric Synthetic Aperture Radar (InSAR) has seen its effectiveness in wide-range, high-resolution deformation monitoring, which provides detailed (up to 1 m spatial resolution) and accurate (several millimiters or less) surface displacements. The persistent scatterers (PS) perform strong capabilities in man-built areas. Yet, its applications still hold drawbacks in semi-natural and smooth surface with specular reflection characteristics, e.g., the aircraft runway, reflected by which the signal is usually weak. Knowing that the airports are covered not only with artificial structures but also natural surface, e.g., bare soil, grass land, a single PS technology may expose its insufficiency in a detailed monitoring. To this end, this study intends to accompany the PS targets with distributed scatterers (DS) that enables the estimation of deformation parameters in a combined way. Basically, the Anderson-Darling test will be used for homogeneous filtering. Phase estimation of DS candidates is to be conducted using a singular value decomposition and coherence-weighted triangulation strategy. The multi-temporal analysis will be carried out based on the CuPS algorithms developed at the Chinese University of Hong Kong (CUHK). Case studies will mainly focus on airports in the Pear River Delta (PRD) region. SAR data from Sentinel-1 A is intended to be used in this study.
[Authors] [ Overview programme] [ Keywords]
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Paper 94 - Session title: Poster Session 1
Tuesday-62 - Assessment of Sentinel-1A/1B SAR interferometry for surface soil moisture estimation
Conde, Vasco (1); Catalão, João (1); Nico, Giovanni (2) 1: IDL, Faculdade de Ciencias, Universidade Lisboa, Portugal; 2: Consiglio Nazionale delle Ricerche, Istituto per le Applicazioni del Calcolo, Bari, Italy
Show abstract
In this study we investigate the surface soil moisture change effects on C band radar interferometry using a time series of Sentinel-1A / 1B interferometric wide mode acquisitions.
Soil moisture influence on SAR interferometric phase and coherence was first noticed by Gabriel et al. (1986) when analysing an interferogram on agricultural fields. The most intuitive explanation is related with the expansion of the soil (clay) due to the presence of water. However, recent investigations have pointed out that the interferometric effect is not due to soil deformation effect. Experimental results has shown that the vertical expansion of soils due to watering is much smaller than the measured phase shift. De Zan et al. (2014) have proposed an analytical model that relates the interferometric phase and coherence with the dielectric constant of the soil, which in turn is related to the soil moisture. The idea behind the model is that the vertical wavenumber is affected by changes on the dielectric proprieties of the soil. The model was validated with L-band interferometric phases. The aim of this study is to assess the effects of in situ measurements on C-band SAR interferometric phases according to the analytical model proposed by these authors and compare it with Sentinel-1A/1B interferometric phases. For that, Sentinel-1A/1B SAR images and ground measurements of soil moisture were used. The test site is a farm on the alluvial plain of the Tagus estuary, close to Lisbon, where four soil moisture sensors were installed. Three sensors were installed 5 cm above the surface and one sensor at 30 cm above the surface providing a measure of the soil moisture depth gradient. A total of 14 Sentinel-1A/1B SAR images, in ascending and descending mode, dual polarization (VV, VH), from 2016 September 28 to November 28, were used in this study. In order to minimize the temporal decorrelation, one interferogram was computed for every two consecutive SAR images and multilooked for speckle noise reduction. Soil moisture measurements were used to predict the analytical interferometric phases and coherences and compared with the measured interferometric phases in both VV and VH polarimetric channels. Results for the inversion based on phases triplets were also computed for the VV and VH polarimetric channels.
Gabriel, A., Goldstein, R., Zebker, H., 1989. Mapping small elevation changes over large areas: Differential radar interferometry. Journal of Geophysical Research, VOL. 94, NO. B7, P. 9183, doi:10.1029/JB094iB07p09183
F. De Zan, A. Parizzi, P. Prats-Iraola, and P. López-Dekker, “A SAR interferometric model for soil moisture,” IEEE Trans. Geosci. Remote Sens., vol. 52, no. 1, pp. 418–425, Jan. 2014.
[Authors] [ Overview programme] [ Keywords]
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Paper 98 - Session title: Poster Session 1
Tuesday-136 - PyRate: An open source Python software for short-baseline InSAR time series analysis
Garthwaite, Matthew; Lawrie, Sarah; Fuhrmann, Thomas; Basak, Sudipta Geoscience Australia, Australia
Show abstract
In this contribution we will give an overview and demonstration of PyRate, an open source Python software for computing InSAR displacement time series using the short baseline differential InSAR processing strategy. PyRate originated as a Python-translation of the Matlab software Pirate developed by the University of Leeds. The PyRate work flow begins with the import of unwrapped geocoded interferograms from either the GAMMA or ROI_PAC interferometric processing software, and ends with the production of the linear rate map (with uncertainties) and the incremental/cumulative displacement time series. Many of the processing algorithms in PyRate are based on the Matlab equivalents including the network orbital error estimation, and linear rate map algorithms. Development of the software has been conducted to form a component of Geoscience Australia’s InSAR processing system running on the National Computational Infrastructure’s multi-node distributed-memory high performance machine raijin. As such, the python language has been used in order to provide a portable and cost-free solution to conducting time series analysis that is scalable from desktop machines for small area processing to large multi-node super computers for conducting regional or continental-scale analyses using parallel processing.
Existing python packages have been re-used where possible to abstract functionality from the software: The GDAL library is used to handle I/O file operations; NetworkX implements graph theory algorithms for manipulating interferometric networks; PyAPS developed by Caltech provides atmospheric corrections based on the ECMWF ERA-Interim global weather model. Furthermore, PyRate follows modern software engineering practices and has been thoroughly unit tested.
We will validate PyRate-derived Sentinel-1 InSAR displacement time series results against results from other software packages and external geodetic data using a case study in the Sydney Basin, Australia. In this region, subsurface longwall coal mining is causing centimetre-level subsidence anomalies at a spatial scale on the order of a kilometre. Currently, a stack of thirty-four Sentinel-1 Interferometric Wide Swath images covering the study region have been acquired with a revisit of 12 days since August 2015. GPS-derived coordinate time series from two continuously operating stations recording since July 2016 will be used as external validation for the InSAR time series analysis. The GPS analysis of the first four months of data indicate that one of these sites is stable within a couple of millimetres whereas the other has already recorded non-linear deformation at the centimetre-level in vertical and horizontal components during the passing of the subsurface longwall operations.
PyRate will be available via PyPI, the python package index, and through Github by the time of the meeting (https://github.com/GeoscienceAustralia/PyRate). We are inviting community participation and collaboration on the testing and further development of PyRate. Feedback on the experiences of users when processing data from different SAR sensors and in different areas of interest will help to focus future development and improvements to the PyRate software.
[Authors] [ Overview programme] [ Keywords]
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Paper 99 - Session title: Poster Session 1
Tuesday-21 - Australian experience with Sentinel-1: two earthquake case studies
Lawrie, Sarah (1); Garthwaite, Matthew (1); Fuhrmann, Thomas (1); Koulali, Achraf (2); McClusky, Simon (2) 1: Geoscience Australia, Australia; 2: Australian National University, Australia
Show abstract
The use of repeat-pass differential InSAR to quickly identify the extent of surface deformation resulting from crustal earthquakes is now common place in many parts of the world, with many groups providing near-real-time routine processing of freely available Sentinel-1 SAR imagery. Surface deformation patterns derived in this way can assist emergency response teams to concentrate their recovery efforts on the potentially most damaged regions whilst also assisting field survey teams to focus their resources in the correct area in order to be able to record vital post-event information such as infrastructure damage, surface ruptures and where to deploy temporary ground sites.
In Australia, the occurrence of strong earthquakes (> M5.0) is uncommon as the continent is considered to be tectonically stable relative to other plate boundary zones. The Australian continent does record low magnitude (M1-3) earthquakes on a regular basis, but most are not felt or do not adversely impact the human population. However, Australia has experienced earthquakes with M6 or greater, with seven such earthquakes recorded since 1968.
On 20 May 2016 UTC, a M6.1 earthquake occurred at a depth of ~10 km on a thrust fault in the Petermann Ranges, a remote region in the Northern Territory (NT). This was the largest earthquake Australia has experienced since 1997. The remote location of this earthquake meant that there was no infrastructure damage, but it was felt in the closest township of Yulara. Given the magnitude of this event was an uncommon occurrence, Geoscience Australia (GA) quickly mobilised a field team to deploy a temporary seismometer network to record aftershocks. Shortly after this event, an earthquake measuring M5.1 occurred on 28 May 2016 UTC in Norseman, Western Australia (WA) on a normal fault with a depth of ~10 km. No field team was deployed to Norseman since all resources were already focussed on the earlier Petermann Ranges earthquake. However, there was interest in studying the surface deformation remotely using InSAR.
More often than not in Australia, InSAR cannot be used to attempt to image coseismic deformation of earthquakes due to the lack of pre-earthquake SAR images for the epicentral area. Fortunately in the case of both of these earthquakes, recent descending-pass Sentinel-1A images had been acquired (25 Oct 2015 – NT and 20 Oct 2015 - WA) so a request was made to the European Space Agency (ESA) for a post-earthquake acquisition. In addition, an ascending-pass ALOS-2 image was available prior to the Petermann Ranges earthquake and so a request was made to the Japanese Aerospace Exploration Agency (JAXA) for a post-earthquake acquisition.
The acquired Sentinel-1A Interferometric Wide Swath (IWS) data and ALOS-2 Fine beam data was processed using the GAMMA software. Several difficulties in processing Sentinel-1 IWS data were encountered that inhibited the rapid production of interferograms for use by the field team. These challenges will be presented in this contribution. The conceptually simpler ‘stripmap’ format of the ALOS-2 fine beam data resulted in the quick turnaround of the interferogram following download of the post-earthquake image acquisition. The ALOS-2 interferogram revealed a complex surface rupture pattern which helped the field team to focus further mapping efforts. Furthermore, features identified through phase discontinuities and coherence changes correlated with field measurements and high resolution optical imagery. Once successfully processed, the Sentinel-1 interferogram for the Petermann Ranges earthquake was much more de-correlated than ALOS-2, particularly in the near-field region of the surface rupture. The Sentinel-1A interferogram for the smaller Norseman earthquake exhibited no obvious deformation fringes. This appears to be due to the earthquake occurring too deep and having a magnitude too small to be detected by InSAR.
Work is currently being undertaken to develop a fault-slip distribution model for the Petermann Ranges earthquake by conducting a joint inversion of the descending Sentinel-1A and ascending ALOS-2 interferograms, and the results will also be presented in this contribution.
[Authors] [ Overview programme] [ Keywords]
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Paper 113 - Session title: Poster Session 1
Tuesday-52 - An improved data integration algorithm applied to the study of the 3D displacement field due to the 2014 Napa Valley earthquake
Polcari, Marco; Albano, Matteo; Bignami, Christian; Stramondo, Salvatore Istituto Nazionale di Geofisica e Vulcanologia, Italy
Show abstract
In this work, we propose an improved algorithm to constrain the 3D ground displacement field
induced by fast and sudden surface deformation phenomena such as an earthquake or a landslide.
Based on the integration of different data, we estimate the three displacement components by
solving a function minimization problem from the Bayes theory.
We exploit the outcomes from SAR Interferometry (InSAR), Global Positioning System (GPS) and
Multiple Aperture Interferometry (MAI) to retrieve a complete 3D knowledge of a surface
displacement field. Any other source of information can be added to the processing chain in a
simple way, being the algorithm computationally efficient. Furthermore, we use the intensity Pixel
Offset Tracking (POT) to locate the discontinuity produced on the surface by a sudden deformation
phenomenon and then improve the GPS data interpolation. This approach allows to be independent
from other informations such as in-situ investigations, tectonic studies or knowledge of the data
covariance matrix.
We applied such a method to investigated the ground deformation field related to the 2014 Mw 6.0
Napa Valley earthquake, occurred few Km far from the San Andreas Fault system.
[Authors] [ Overview programme] [ Keywords]
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Paper 120 - Session title: Poster Session 1
Tuesday-95 - SAR Sensor Full Pointing Calibration Strategy Using Doppler Centroid and Permanent Scatterers
Recchia, Andrea (1); Mancon, Simone (1); Monti Guarnieri, Andrea (2); Giudici, Davide (1) 1: Aresys s.r.l., Italy; 2: Politecnico di Milano, Italy
Show abstract
The SAR satellites require a very good pointing control in order to assure high quality images and good interferometric performances. This is particularly true for modern sensors, implementing advanced acquisition techniques such TopSAR. For this reason modern SAR sensors (like Sentinel-1) are equipped with very accurate attitude control systems requiring, after launch, a calibration procedure in order to obtain the expected performances.
The pointing calibration is usually performed during the Commissioning Phase of a SAR mission and involves the usage of Elevation Notches to adjust the roll pointing and of transposers to adjust the yaw and pitch pointing. The main limitation of this strategy is the sparseness of the available calibration sites. Elevation Notches require very homogeneous scenes to be effective and hence shall be performed over the Rain Forest. On the other hand transponders are expensive and can only be deployed in few calibration sites. This means that possible orbital trends in the sensor pointing errors cannot be captured by the currently used calibration strategy.
The present paper focuses on this issue and proposes a new method to perform a full sensor pointing calibration, exploiting the Doppler Centroid estimates from SAR acquisitions over still land areas for yaw and pitch calibration and Permanent Scatterers from SAR interferometric stacks for roll calibration. The advantage of this calibration technique is that calibration sites from all over the world can be selected in order to get full orbit pointing calibration, fundamental for modern SAR applications.
The yaw and pitch calibration is performed exploiting the DC estimates from stationary scenes. The data acquired by space-born SAR satellites are naturally affected by a Doppler shift, due to the relative motion between the platform and the imaged ground scene. Assuming a perfectly calibrated pointing control system such Doppler shift can be fully predicted. The proposed calibration method starts from a grid of DC estimates from the data in the imaged scene and performs a Singular Value Decomposition to identify the pointing plane best fitting the available DC estimates.
The roll calibration is performed through the processing of interferometric stacks exploiting natural PSs. Usage of PSs for radiometric calibration of SAR sensors is a well-known technique allowing to assess long term radiometric stability. Moreover, from a reformulation of the model, it is possible to account for an error in the antenna pointing in elevation and to solve for this by exploiting measures on PSs located all over the swath.
The combination of this two calibration methods will allow to get a full 3D sensor calibration. This process, repeated in time, will allow to identify any possible trend in the sensor pointing which, corrected, will allow to increase the accuracy of the SAR applications.
The first part of the paper will introduce the proposed pointing calibration methodologies. The second part of the paper will provide the results of the proposed pointing calibration strategy applied to Sentinel-1A&B datasets.
[Authors] [ Overview programme] [ Keywords]
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Paper 122 - Session title: Poster Session 1
Tuesday-99 - Assessing Signal Penetration Into Ice And Snow For The TanDEM-X Mission
Krieger, Lukas; Johnson, Erling; Abdel Jaber, Wael; Floricioiu, Dana German Aerospace Center (DLR), Germany
Show abstract
Surface elevation changes of an ice sheet characterise its reaction to variations in the regional climate. A warming climate, ultimately causes enhanced surface melting and dynamic thinning of a glacier [van den Broeke et al. 2009], both of which contribute to global sea level rise.
One mean to estimate surface elevation changes is DEM differencing [Abdel Jaber et al. 2013]. In contrast to classical radar or laser altimeters the differencing of high resolution DEMs can give insight into the spatial extent and pattern of the thinning process. Since its start in June 2010, the TanDEM-X (TDM) mission offers great potential to study ice sheet thinning with high spatial detail. As great parts of Greenland and all Antarctica are not covered by SRTM data, subsequent TDM DEMs from bistatic acquisitions are the only InSAR dataset that provides elevation measurements for all Ice sheets and Ice fields on earth, often with multiple acquisitions during the course of several years.
A problem for InSAR DEMs, that are generated from TDM data, is the signal penetration of microwaves into dry ice and snow. The penetration depth is depending on the dielectric properties of the snow and ice cover and the carrier frequency of the signal [Stiles et al. 1981]. In case of a wet snow or ice surface this effect can be neglected for both X- and C-band, because the actual signal penetration is much lower than the vertical accuracy of the InSAR DEMs.
However, in very cold and dry climate conditions, signal penetration of X- and C-band waves can be in the order of several meters. The effect is therefore substantial, when InSAR DEMs acquired in times of unequal snow and ice conditions, are differenced.
One approach to account for signal penetration is the correction of InSAR DEMs with coincident laser altimetry measurements with lower spatial resolution, but no signal penetration. Unfortunately, since the deactivation of ICESat in February 2010, there is no operational laser altimetry satellite in orbit. With the ATM instrument of operation IceBridge, there is only an airborne replacement for a laser altimeter that tracks the actual snow and ice surface.
Having limited concurrent laser altimetry measurements for TDM acquisitions, it is of great value to assess additional means of estimating the InSAR signal penetration depth for TDM. We propose a dual frequency approach by evaluating elevation measurements from the SIRAL instrument on the Cryosat-2 platform together with TDM data. As SIRAL operates in Ku-band, the signal penetration is lower than in X-band at constant snow and ice conditions.
According to [Stiles et al. 1981] the penetration depth dp of a microwave signal into dry snow is dp ≈ λ/2π ∗ (√e'')/e' , where λ is the wavelength of the signal and e', e'' are the real and imaginary part of the dielectric constant. Assuming dielectric snow and ice properties to be constant between the measurements we can use the difference in penetration depth ∆dp to solve the system of equations for combined snow and ice parameters. Therefore, this approach can be used to correct InSAR DEMs for signal penetration. We use coincident ATM elevation measurements from operation IceBridge to validate our method.
[Authors] [ Overview programme] [ Keywords]
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Paper 126 - Session title: Poster Session 1
Tuesday-57 - A Synthetic Approach to Estimate Earthquake Source Parameters Using InSAR Observations and Strong Ground Motion data (The 2008 Qeshm island earthquake in Iran)
Golshadi, Zeynab (1); Pakdaman, Mohammad Sadegh (2) 1: Department of Physics of the Earth, Institute of Geophysics, University of Tehran, Tehran, Iran; 2: Department of Environment and Energy at Science & Research Branch, Islamic Azad University, Tehran, Iran
Show abstract
Prognostication of realistic ground motion that includes absolute amplitudes and the full wave train of arrivals is essential to comprehensively narrate earthquake hazard and can give noteworthy insight into the poorly understood tectonics of the area. In order to estimate realistic ground motion from probable earthquake, awareness of earthquakes source parameters in area is indispensable. Earthquake source parameters serve as a substantial database for the generalists and synthesizers in seismology and as an initial starting point for the applied theoreticians. The routine determination of source parameters, could make feasible a new level of understanding in many seismological studies that would parallel the use of reported earthquake locations to demonstrate boundaries of tectonic plates. It can provide a wealth of critical information for earthquake hazard assessment and for improved understanding of the earthquake process.
The primary purpose of this study are to: (1) ameliorate estimation of source parameters and computer simulations of earthquakes (2) examine the effect of a range of rupture parameters on synthesized strong ground motion, (3) demonstrate that models derived from step by step modeling of InSAR observation (L-band, C-band and X-band respectively), can be used to predict very realistic source parameters.
We have used Qeshm 2008 earthquake to demonstrate the rich potential of using three InSAR observation sets (L-band, C-band and X-band) to measure coseismic fault zone deformation and consequently, the causative fault parameters of Qeshm 2008 earthquake.
Qeshm is the biggest Persian Gulf Island located parallel to Iran’s southern coasts, in Hormoz Strait, between the latitudes of 26°32΄ and 26°59΄ north and also longitudes of 55°15΄ and 56°17΄ east. The 2008 Qeshm earthquake occurred at 14:30 IRST (11:00 UTC) on 10 September and lasted at least 30 seconds. It had a magnitude of 5.9 on the moment magnitude scale and 6 on the surface wave scale. It was followed by five aftershocks of M 5.0 or greater over the next ten months.
Applying InSAR chain processing for modelling earthquake parameters according to the formulation of (Okada, 1985) because of covering the wide area, acceptable precision and being inexpensive is highly been considered. Interferometry SAR analysis is especially useful because of its high resolution and precision. Factors that limit InSAR include atmospheric perturbations and that it can only determine one component of displacement in the direction of line of sight.
InSAR has become a commonly used technique to measure surface deformation. Measurements by the SAR satellites are made obliquely below the satellite during both ascending orbits (where observations are made from the west) and descending orbits (where observations are made from the east). Horizontal deformation therefore causes inconsistencies between ascending and descending interferograms. Two pairs of ascending and descending ALOS-1/PALSAR, ENVISAT/ASAR and TerraSAR-X images were available to study the coseismic deformation field of the Qeshm 2008 earthquake.
Interferometry relies on the constructive and destructive interference of electromagnetic waves from sources at two or more vantage points to infer something about the sources or the relative path length of the interferometer (Simons & Rosen, 2015). Differential interferometry aims the measurement of ground deformation using repeat-pass interferometry (Hanssen, 2001). In this method, we use phase difference of two or more SAR image with same geometry to retrieve deformation phases. In fact, for DInSAR, the interference pattern is constructed from two complex-valued SAR images, and interferometry is the study of the phase difference between two or more images acquired from different vantage points, different times, or both (Simons & Rosen, 2015).
In this paper we describe a new approach that allows us to improve the source parameters and simultaneously modify the solution for the moment tensor. This, in effect, yields the best source parameters, which for major earthquakes need not be the same as the point of initiation of rupture on the surface (sometimes it did not reach the surface).
We performed step by step inversion procedure (L-bandà C-bandà X-band) to obtain best fit between observed and synthetic displacement, along with interferograms. In this approach, obtained ranges for each parameters in inversion are used as input ranges for next inversion procedure. For all steps, Marquardt algorithm (Marquardt, 1963) has used. Marquardt algorithm can be seen as a regularization of the Gauss-Newton method. The steps are based on coverage area with three satellite images and the wavelength of them. The processing began from biggest coverage area and lowest resolution because of higher wavelength. Thus, in first step L-band inversed and analyzed, then C-band and finally X-band. The output results from first processing including a range for all source parameters, will be initial values as input for next step.
Though the source parameters are assumed completely unknown, we must set, for each parameters, a range of values between a minimum and a maximum. In fact, the basic premise for calculating source parameters of an earthquake using InSAR observations will be output results from satellite that has biggest coverage area and higher wavelength. The coseismic displacement of Qeshm earthquake is modeled via Non-Linear inversions, in order to retrieve the position and parameters of the causative fault. With the Non-Linear inversion, we try to reproduce the observed displacement by means of a geophysical source with unknown parameters and all its parameters must be inferred from InSAR observations.
The first search ranges for nonlinear inversion of L-band data were set to 0.5–25 km for length, width and depth, 10-250° for strike, 10-90° for dip, 5-180° for rake during the inversion for the source parameters. Then the resulted ranges for every parameter were used for input parameters of C-band inversions, finally the output results from C-band inversion were used for input parameters of X-band inversion as input ranges.
The mentioned procedure was done to achieve more precise result for source parameters of Qeshm earthquake. The final set parameters for earthquake are: 8.2 km, 22 km and 6.6 km for width, length and depth of fault, 31°, 70° and 10° for strike, dip and rake and 388343.8 and 2965056 for easting and northing respectively.
Source parameters of the 2008 Qeshm earthquakes have already been computed using diverse studies, including seismicity, the earth’s surface deformation field, and rupture characteristics. Each of these studies proposes different mechanisms for this earthquake.
Also we performed step by step inversion (X-bandà C-band àL-band) and obtained different parameters from L-band to C-band procedure. At last for best comparison between the obtained interpretations with other studies carried out on Qeshm earthquake (CMT solution, Nissen report (E. Nissen et al., 2010) and our study), we made synthetic strong ground motion with the help of Empirical Green’s Function method in two nearby stations (Suza and Tomban) and compared them with observed one. The best fit between observed and synthetic accelerograms was considered as best report for causative fault parameters of Qeshm earthquake.
Strong ground motion data provides researchers with very important information about the rupture processes of earthquakes, simulation of ground motion and consequently source parameters of an earthquake. In Empirical Green’s function method, a major earthquake is modeled by a collection of point sources distributed over the fault plan that their responses are approximated by the ground motion of the biggest and closest associated aftershock. In this way, the effects of true earth structure are included in the modeling process and the results are more precisely. The study is based on data recorded by the Iranian Strong Motion Network which is run by the Building and Housing Research Center (BHRC). The data were recorded by three-component SSA-2 accelerometers with a threshold of 10 Gals at a sampling rate of 200 samples per second. All of components of these data are used in this study.
The best approach as Empirical Green’s function method that has been one of the most powerful and applied methods for predicting strong ground motion induced by large earthquakes presented by (Irikura, 1986).
Simulation of ground motion from large earthquakes using small earthquakes (subevents) as Green's functions and summing them in a random way is basis of this method. This method is based on the concept of self-similarity (Brune, 1970; Kanamori & Anderson, 1975) that assumes a constant stress drop for earthquakes of all magnitudes and provides scaling relations for relating faulting parameters of varying size earthquakes that are from a single source.
The recording stations were located at epicentral distances ranging from 14 to 263 km. The acceleration records from all components were at first corrected for baseline correction following the algorithm developed by (Boore, 2001).
The final comparison are presented as percentage for accuracy. These results obtained from comparison between observed and synthetic strong ground motion in two stations (Suza and Tomban) in three components (longitudinal (L), vertical (V) and transverse (T) components).
For this comparison, the maximum absolute value was used for comparing between observed and synthetic acceleration, velocity and displacement data. To compare between Fourier and response spectrum, the correlation of observed and synthetic one was used.
Based on obtained accuracy and setting the acceleration as reference for comparing between observed and synthetic accelerograms, the component L has more reliable accuracy in two stations for our procedure (with 95% and 93% accuracy). In V component, the best accuracy is related to CMT catalog (with 91% and 98% accuracy) and for T component the best fit is related to our approach (with 96% and 91% accuracy). In velocity and displacement, we are faced with variable results for four procedure. Overall results from Fourier and Response spectrum show that the best set parameters related to InSAR Modelling L to X (with 79% accuracy) and CMT catalog (with 65% accuracy). At last, overall accuracy with same weighing to each category (Acceleration, velocity, displacement, fourier and response specrum) for Suza and Tomban stations was calculated. In Suza station, the best accuracy is related to: InSAR Modelling L to X (74%), InSAR Modelling X to L (64%), (Nissen, 2010) (59%) and CMT catalog (59%) set parameters respectively. In Tomban station, the best accuracy is related to: InSAR Modelling L to X (84%), InSAR Modelling X to L (73%), CMT catalog (71%) and (Nissen, 2010) (63%) set parameters respectively. Comparison between observed and synthetic strong ground motion shows that our procedure results more precise source parameters compared with other literatures. Our procedure allow us to move forward from results with larger coverage area and less resolution to greater resolution to obtain greater accuracy for fault parameters.
[Authors] [ Overview programme] [ Keywords]
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Paper 129 - Session title: Poster Session 1
Tuesday-22 - Vertical ground motions of the San Salvador metropolitan area (AMSS) seen at the ALOS InSAR data
Kowalski, Zbigniew (1); Graniczny, Marek (1); Przyłucka, Maria (1); Šebesta, Jiří (2); Chavez, Alexander (3) 1: Polish Geological Institute, Warszawa, Poland; 2: Czech Geological Survey, Prague, Czech Republic; 3: Unidad Ambiental, OPAMSS, San Salvador, El Salvador
Show abstract
Vertical ground motions of the San Salvador metropolitan area (AMSS) seen at the ALOS InSAR data
Zbigniew Kowalski1 e-mail: zkow@pgi.gov.pl
Marek Graniczny1 e-mail: mgra@pgi.gov.pl
Jiří Šebesta2 e-mail: sese@seznam.cz
Jose Alexander Chavez Hernandez3 e-mail: jalexanderchavez@gmail.com
Maria Przyłucka1e-mail: msur@pgi.gov.pl
1Polish Geological Institute (PGI) – National Research Institute,Warszawa, Poland
2Czech Geological Survey, Prague, Czech Republic
3Unidad Ambiental, OPAMSS, San Salvador, El Salvador
Keywords:San Salvador, volcanos, seismic activity, PSInSAR, interferometry, geohazards
The city is located in plateau between the San Salvador volcano and IIopango caldera, a region of high seismic activity. The city's average elevation is 659 m a.s.l, but ranges from a highest point of 1,186 m a.s.l to a lowest point of 596 m a.s.l. The municipality is surrounded by these natural features of the landscape: southward by the Cordillera del Balsamo (Balsam Mountain Range); westward by the San Salvador volcano and Cerro El Picacho, the highest point in the municipality at 1,929 m a.s.l. San Salvador Volcano was dormant since its last eruption in 1917, but has been active recently. East of the municipality lies the San Jacinto Hill and the caldera of Lake Ilopango, the largest natural body of water in the country with an area of 72 square km. The caldera is seismically active, but has not erupted since 1880.
The city has suffered from many severe earthquakes, the most disastrous of which occurred in 1854. The San Salvador volcano erupted again in 1917,resulting in three major earthquakes that damaged the city so extensively the government was forced to temporarily move the capital to the city of Santa Tecla (known at the time as Nueva San Salvador). The 1986 San Salvador Earthquake struck on October 10, 1986, causing considerable damage to the city and surrounding areas. Between 1,000 and 1,500 people are believed to have been killed, and over 10,000 people were injured. 200,000 people were left homeless after the earthquake and a week of minor aftershocks. The 2001 El Salvador earthquakes struck El Salvador on January 13 and February 13, 2001, resulting in considerable damage to the city, especially in Las Colinas suburb, where a landslide destroyed homes and killed many people.
The interferometric analysis of San Salvador has included 20 ALOS scenes – L band, collected between 31 December 2006 and 26 February 2011 (Fig. 1). It has revealed presence of vertical ground deformation. Persistent Scatterer Interferometry (PSInSAR) confirmed subsidence about 97% of San Salvador Metropolitan Area (AMSS). Subsidence is observed mainly within Quaternary silicic volcanic rock, mostly tuffs. The biggest subsidence is situated in the eastern part of AMSS, close to the Lake Ilopango, with values exceeding 10 mm/yr. Small uplift was confirmed within young Quaternary and mafic volcanic rocks, on the north slope of the San Salvador volcano. The another interesting phenomenon could be observed in northern – central part of the city (Department Mejicanos). This area could be characterized generally as stable with small predominance of the uplift up to 5 mm/yr. Due to the high seismicity of Salvador satellite interferometric monitoring should be continued.
Authors of this paper would like to express thanks to providers of the Alaska Satellite Facility (ASF) website for access to the ALOS satellite images from San Salvador.
[Authors] [ Overview programme] [ Keywords]
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Paper 136 - Session title: Poster Session 1
Tuesday-122 - Automated InSAR processing system for imaging large earthquakes
Feng, Wanpeng; Samsonov, Sergey Canada Center for Mapping and Earth Observation, Natural Resources Canada, Canada
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Following success of RADARSAT-1/2, the RADARSAT Constellation Mission (RCM) will be launched in 2018 and will consist of three identical C-band SAR satellites. With enhanced imaging capabilities, RCM will provide SAR acquisitions with the four days revisit cycle in both StripMap and ScanSAR modes. Short revisit cycle will improve temporal correlation and increase capabilities of deformation mapping. Combining with ongoing (e.g. Sentinel-1A/B, ALOS-2) and coming (e.g. RCM and NISAR) SAR missions, the awaiting time of SAR observations for emergency geohazard events will be largely reduced. To fit the requirement on processing loads of expected SAR data and efficiently generate deformation products from these SAR data, an automated InSAR processing system (gInSAR) is being developed at the Canada Center for Mapping and Earth observation (CCMEO), which will provide regular InSAR processing service for the Canadian Government. Targeted users even without basic InSAR knowledge will be able to obtain InSAR deformation products by submitting online request.
In this study, we present deformation results computed from RADARSAT-2, Sentinel-1A/B and ALOS-2 SAR data for the rapid response to recent large destructive earthquakes, including 2015 Mw7.3 Tajikistan earthquake, 2016 Mw6.2 Taiwan earthquake, 2016 M6 Italy earthquake sequence and 2016 Mw7.8 Kaikoura (New Zealand) earthquake. SAR data flow management and SAR data processing with gInSAR are discussed through these realistic applications. In particular, the SAR data in TOPS imaging mode that also will be provided by RCM, needs additional efforts to implement InSAR generation automation. A flexible control on conducting TOPS interferometry with single or several sub-swaths and bursts of TOPS data has been realized in the current version of gInSAR. In addition, large deformation caused by shallow earthquakes can result in significant decorrelation in the vicinity of the fault rupture, where interferometric phase cannot be revealed properly with a traditional InSAR processing chain. To recover more explicit deformation details, a subpixel-compensate strategy is proposed in gInSAR. The improved results for the 2016 Mw7.8 Kaikoura earthquake present clear near-filed multiple deformation segments that can play important roles for fault identification and slip modelling. This implies the practicability of the proposed strategy for large deformation events. A multi-dimensional small baseline subset analysis (MSBAS) can also be followed under gInSAR if required. Some of these suggested strategies can also be applicable to other open source InSAR packages.
[Authors] [ Overview programme] [ Keywords]
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Paper 140 - Session title: Poster Session 1
Tuesday-138 - The Method of the InSAR/INS Integrated Navigation Based on Interferograms
Xiang, Maosheng; Fu, Xikai; Chong, Jinsong Institute of Electronics, Chinese Academy of Sciences, China, People's Republic of
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The existing navigation systems have lots of problems: Inertial Navigation System (INS) is not accurate enough to eliminate drifts of platforms because of the rapid growth of systematic errors; the resolution of the terrain aided navigation system is low; the Global Positioning System (GPS) signals of the GPS/INS navigation system are susceptible to be interfered; the SAR/INS integrated navigation system is not able to implement three-dimensional localization, and it cannot get the attitude of the platform. In order to solve those problems, this article presents the method of InSAR/INS integrated navigation system based on the interferogram matching.
Let us refer to Fig.1, where the flow chart of InSAR/INS integrated navigation system is depicted. The procedures of the InSAR/INS integrated navigation can be divided into five steps. Firstly, the actual interferograms are obtained by the InSAR system in the real-time processing. Secondly, the referenced interferograms are generated based on the digital elevation database, flight trajectory and imaging parameters of the InSAR system. Thirdly, the previous two interferograms are matched by Scale-Invariant Feature Transform (SIFT) algorithm to obtain the location shift in azimuth and range direction. And then we will inverse the position and attitude offset according to the InSAR three-dimensional positioning model and inversion model. At last, the position and attitude information and the IMU information are set to the combined filter to obtain the navigation output.
Fig.1 The flow chart of InSAR/INS integrated navigation system
The InSAR/INS integrated navigation system has the following advantages: (1) compared with the SAR system, the InSAR system is able to accomplish three-dimension Positioning; (2) interferometric phase is sensitive to elevation information and the attitude of the platform, especially the roll angle, so that the roll angle can be inversed through the interferometric phase in high precision; (3) the match of interferogram is more efficient and accurate than DEM and image matching, and SIFT has fault tolerance of interferogram whirl and diversification of interferogram scale.
In this article, we will introduce the theory and method of the InSAR/INS integrated navigation based on interferogram matching. It is obvious that the location errors related not only to the platform location, but also to the platform attitude. So we can estimate the position errors and attitude errors by solving nonlinear equations, which are gained through InSAR three-dimensional positioning model and inversion model.
We verify the validity of interferogram matching and the inversion of position and attitude by experiment. The results of the experiment are shown in Fig.3. The interferogram matching result is shown in Fig.3 (a) with the actual interferogram on the left and the referenced interferogram on the right, and the matching points’ location shift in azimuth and range direction are shown in (b) and (c). Apparently, the differences between the simulated and theoretical result are quite tiny.
(a) interferogram matching result (b) location shift of azimuth (c) location shift of range
Fig.3 the results of the experiment
Finally, the position and attitude information are inversed through the inversion model in high precision. The errors of position inversion are less than 2 meter, and the errors of attitude inversion are less than 0.02 degree. Therefore, the method of the InSAR/INS integrated navigation based on interferogram matching is feasible and efficient.
[Authors] [ Overview programme] [ Keywords]
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Paper 149 - Session title: Poster Session 1
Tuesday-81 - The use of the Sentinel-1 InSAR Browse service on ESA’s Geohazards Exploitation Platform for improved disaster monitoring
Martinis, Sandro (1); Brcic, Ramon (1); Plank, Simon (1); Tavri, Aikaterini (2); Rodriguez Gonzalez, Fernando (1) 1: German Aerospace Center (DLR), Germany; 2: Technical University of Munich, Germany
Show abstract
Due to the systematic conflict-free observation scenario of the Sentinel-1 mission most parts of the Earth’ surface will be covered within a repeat cycle of up to six days. This leads to new applications in time-series analysis and SAR Interferometry (InSAR), which make this Synthetic Aperture Radar (SAR) mission particularly suitable for monitoring geohazards and for rapid mapping activities and to new challenges in handling big data.
Via the Geohazard Exploitation Platform (GEP) of ESA, a Sentinel-1 InSAR Browse service, developed by DLR and Terradue, is provided, which gives users direct access to a powerful processing capacity to exploit large Earth-observation datasets. Based on pairs of Sentinel-1 data from consecutive passes this service provides an interferometric product at 200m resolution with systematic processing over tectonic areas as defined by the CEOS Working Group of Disasters. In addition, a 50m resolution product are also delivered to a pre-defined group of expert users working in ESA research and development studies.
The focus of this work is to test the synergistic use of amplitude and coherence data of the Sentinel-1 Browse service for disaster monitoring applications in the field of flood mapping, fire detection and earthquake damage assessment. This work was conducted in the frame of the ESA funded project ASAPTERRA.
Within this presentation an overview of the main methodological developments in each disaster topic is given and demonstrated in selected test areas:
In flood mapping DLR’s amplitude data-based fully automatic Sentinel-1 Flood Service was modified to integrate coherence information in a fuzzy logic post-processing step to exclude water look-alike areas of low backscatter using coherence data. This extension has been tested on two time-series of 14 and 7 Sentinel-1 acquisitions in flood-affected areas at Evros River at the border between Greece and Turkey and at Shannon River, Ireland, respectively.
A semi-automatic object-based approach consisting on empirical thresholding and region growing procedure has been developed for the extraction of burnt areas in Sentinel-1 time- series data and tested in fire affected areas near Marseille/Vitrolles, France (4 interferometric data pairs), and in the northern part of Portugal (5 interferometric data pairs). While it was not possible to derive the burnt area using the amplitude data in both test sites, a significant loss of coherence over burnt scars between co-event and pre-event data pairs could be identified and used for the extraction of the crisis information. Best results have been achieved by classifying the absolute deviation of the co-event coherence to the mean time series value.
In the context of earthquake damage assessment, a suitability analysis of the data of the InSAR Browse service was performed on a test site covering parts of the city of Amatrice, Italy, which has been affected by a strong earthquake on 24/08/2016. A semi-automated object based classification of the damaged area based on the pre-event coherence pair (15/08/-21/08/2016) and the absolute coherence difference of the data pairs of 15/08/-21/08/2016 and the co-event 21/08/-27/08/2016 was performed and showed a satisfying agreement with the rapid mapping results of the Copernicus Emergency Management Service (EMS) of the European Commission.
[Authors] [ Overview programme] [ Keywords]
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Paper 154 - Session title: Poster Session 1
Tuesday-48 - Coseismic And Post-seismic Displacements Associated With 2010 Mw 6.5 Rigan Earthquake In SE Iran Revealed By Space-borne Radar Interferometry Observations
Amiri, Meysam (1); Mousavi, Zahra (1); Tolomei, Cristiano (2); Atzori, Simone (2); Motaghi, Khalil (1); Salvi, Stefano (2) 1: Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, Iran; 2: Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy
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Iranian plateau and surrounding areas are affected by the convergence between Arabian and Eurasian plates, where the deformations are accommodated by young Zagros collision, old Alborz and Kopeh Dagh collisions, Makran subduction and shear zones in east Iran. This variety of deformation makes Iran an ideal natural laboratory for measuring kinematics and dynamic activities. Earthquakes with magnitude greater than 6 caused more than 120,000 victims in the last century. This indicates necessity of seismic risk assessment inside Iran. Mw 6.6 Bam earthquake occurred in 2003 with 40,000 victims is one of the deadliest earthquakes in Iran which is located in shear zones at southeast Iran. On 20th December 2010, an earthquake with Mw 6.5 occurred in Rigan, a small town in the desert south of Bam city. The earthquake epicenter was in a low population area so, luckily, it caused only few casualties. 37 days later, on 27th January 2011, another earthquake (Mw 6.2) stroke an area at ~20 km southwest the first earthquake.
To study the source parameters of this doublet, Walker et al., (2016) used SAR interferometry, multiple-event relocation, body-waveform modelling and field measurements of surface rupture to show that the 20th December 2010 earthquake showed a mean right-lateral slip of ~1.3 meters on a vertical fault trending ∼210° whilst the 27th January 2011 resulted in ∼0.6 m slip value on a conjugate left-lateral fault striking ∼310°.
In 2010, National Cartography Center (NCC) of Iran established a geodetic network of 20 stations (bedrocks sites with forced antenna centering) in the study area. The results of two GPS measurement surveys show a significant post-seismic deformation signal in the area. Considering the active faults distribution, post-seismic deformation retrieved from GPS sites and the 76 aftershocks encouraged us to better investigate and model the post-seismic deformation related to the 2010 and 2011 earthquakes. Post-seismic studying provides information about rheology of the surrounding region and improves our knowledge about the strain release after the earthquake.
In this study, ALOS-1 (from Japan Space Agency, JAXA) Synthetic Aperture Radar (SAR) images, before and after the earthquake, were processed to retrieve the source parameters associated with the Rigan 2010 earthquake. COSMO-SkyMed (from Italian Space Agency, ASI) images spanning the temporal interval between 4th February 2011 and 15th July 2011 are used to investigate the post-seismic deformation following both the earthquakes. The COSMO-SkyMed and ALOS-1 images were processed using the SARscape® software (SARMAP, CH). We joined two frames along the same orbit to cover the whole deformation field, resulting in 30 ascending and 30 descending datasets, respectively. We applied the Small Baseline Subset (SBAS) algorithm for both ascending and descending tracks to obtain the post-seismic mean velocity map and the relative deformation time series.
Time series analysis reveals a clear post-seismic signal exponentially increasing with time until reaching the rate of more than 10 mm/year. Later, we have modeled the post seismic signal considering a dislocation on a finite fault in an elastic and homogeneous half-space that are the assumptions for the Okada (1985) model. Post-seismic results were modeled adopting a two-step approach: (1) a non-linear inversion was performed to constrain the fault geometry parameters and considering an uniform slip, then (2) a linear inversion was operated to retrieve the slip distribution on the fault plane previously obtained. The best-fit retrieved model for the 2010 Rigan strike-slip earthquake shows that the maximum slip is present on the same area interested by the co-seismic slip model, and already described by Walker et al., (2016).
[Authors] [ Overview programme] [ Keywords]
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Paper 156 - Session title: Poster Session 1
Tuesday-115 - Time series of surface displacement of Arctic glaciers and ice caps from space-borne SAR data
Strozzi, Tazio (1); Wiesmann, Andreas (1); Kääb, Andreas (2); Schellenberger, Thomas (2); McNabb, Robert (2); Paul, Frank (3) 1: Gamma Remote Sensing, Gümligen, Switzerland; 2: Department of Geosciences, University of Oslo, Norway; 3: Department of Geography, University of Zurich, Switzerland
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In consideration of the strong atmospheric warming that has been observed since the 1990s in polar regions there is a need to quantify ice mass loss of Arctic ice caps and glaciers and their contribution to sea level rise. In polar regions a large part of glacier ablation is through calving of tidewater glaciers driven by ice velocities and their variations. Through frequent monitoring based on repeat satellite data the evolution of Arctic glaciers and ice caps can be now recorded at high temporal sampling. Complete ice velocity maps of the Svalbard archipelago can be e.g. regularly computed every 12 days with Sentinel-1 since mid August 2015 using offset-tracking. Dedicated Sentinel-1 campaigns were also accomplished over the Canadian and Russian Arctic. Radarsat-2, ALOS-2 PALSAR-2 and summer optical images offer the opportunity to complement recent Sentinel-1 results in time and space. In many cases historical maps of the 1990's and 2000's can be computed with ERS-1/2, JERS-1, Radarsat-1 and ALOS-1 PALSAR-1. Within the ESA Glaciers_CCI (http://www.esa-glaciers-cci.org) and EC FP7 SEN3APP (http://sen3app.fmi.fi) projects we apply SAR offset-tracking to historical and ongoing satellite SAR data for the monitoring of the ice surface displacement of glaciers and ice caps in the Arctic. Particular attention is paid to Svalbard and the Russian Arctic (Novaya Zemlya, Franz-Josef Land and Severnaya Zemlya). In our contribution we will present selected results obtained with Sentinel-1 data and highlight significant changes of ice surface velocities evident from the comparison with older maps.
The most evident signal over Svalbard is observed for Basin 3 on the Austfonna ice cap, which shows dramatic changes since 1995, but significant accelerations are also depicted on a few other glaciers across the archipelago. Over the southern lobe of Stonebreen on Edgeøya we e.g. observed a slow and steady retreat of the glacier front from 1971 until 2011 followed since 2012 by a strong increase in ice surface velocity along with a decrease of volume and an advance in frontal extension. The considerable losses in ice thickness could have made the tide-water calving glacier, which is grounded below sea level until some 6 km inland from the 2014 front, more sensitive to surface melt-water reaching its bed and/or warm ocean water increasing frontal ablation with subsequent strong multi-annual ice-flow acceleration. A similar process seems already to have started for the southeastern tip of Austfonna, sometimes called Basin-2. Over Novaya Zemlya and Franz-Josef Land Sentinel-1 and ALOS-2 PALSAR-2 results indicates, in comparison to JERS-1 results of 1994-1998 and PALSAR-1 results of 2008/2009, a general steady increase of frontal velocities along with a retreat of frontal positions. A similar general pattern is also observed for most of the glaciers and ice caps on the Severnaya Zemlya Archipelago, with the prominent exception of the western margin of the Vavilov Ice Cap, where a strong increase in ice surface velocity has been observed since 2015 with highest speeds of more than 20 m/day in the summer of 2016 along with a very prominent advance in frontal extension.
[Authors] [ Overview programme] [ Keywords]
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Paper 163 - Session title: Poster Session 1
Tuesday-79 - Multipath Interference in Ground Based Radar Data
Lucas, Célia (1,2); Silvan, Leinss (1); Yves, Bühler (2); Armando, Marino (3); Irena, Hajnsek (1,4) 1: Institute for Environmental Engineering, ETH Zurich, Switzerland; 2: WSL- Institute for Snow and Avalanche Research SLF, Davos, Switzerland; 3: Department of Engineering and Innovation, Open University, Milton Keys, United Kingdom; 4: Microwaves and Radarinstitute, DLR, Oberpfaffenhofen, Germany
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In the framework of a ground based radar campaign in Davos, Switzerland, unexpected fringe-like features, parallel to the topographic contours, were observed in the intensity data as well as in DEM differences (Fig.1) and single pass interferograms. Unlike real interferometric fringes, the phase of the observed features does not cycle through the full two pi cycle but rather undulates around a mean value. Similarly to contour lines, their frequency correlates with the terrain slope angle: the steeper the terrain, the smaller the distance between them. To avoid the usage of the misleading and erroneous term “fringes” and due to the similarity of the observed features with the terrace-like paths produced by grazing cattle on alpine meadows, we named them ochsohypsen, in analogy to the German word Isohypsen for contour lines. In this study the origin of the ochsohypsen was investigated and they were modeled using the real geometry.
We show that the ochsohypsen are multipath interference patterns between waves directly travelling to the target area and waves indirectly reaching it via reflection on a flat surface between the radar and the target area. This reflection may happen on either or both travel directions of the wave. This interference of the two wavefronts is similar to the famous double slit experiment. Constructive and destructive interference of the direct, simple and double reflected indirect waves at the radar generate the observed ochsohypsen. The double slit experiment describes the angular spacing θ f of the interference cycles as θ f = λd [1], with λ the wave frequency and d the separation of the two wave sources. The regular interferometric fringe spacing is given by the same formula with d being the effective perpendicular baseline.
To replicate and prove the origin of the ochsohpysen, a second test site at the Campus of ETH Zurich in Hönggerberg was selected. Similarly to the initial Davos campaign, a ground based, real aperture, fully polarimetric radar interferometer operating in Ku-band was positioned in a way that it was looking upward to the target area, which was separated from the radar by a flat surface. Whereas in Davos, this surface was a lake, in the Hönggerberg test site, it was a field with high grass, exposing an increasing fraction of humid bare soil as the grass was being cut over the course of the experiment. In the Hönggerberg experiment, the increase in reflectivity of the surface through the appearance of bare soil during mowing, lead to an increase in the ochsohypsen intensity. By changing the antenna height above the reflective surface, the frequency of the ochsohypsen changed, following equation [1] defined by the double slit experiment.
At the initial test site in Davos, the lake surface resulted in specular reflection of all waves reaching the lake surface and therewith very strong interference of direct and indirect waves. The Davos lake surface was lowered over the course of the winter due to hydropower production. Therewith the distance d, between the transmitting antenna and the mirrored antenna as shown in Fig.2, increased over the winter season, changing the ochsohypsen frequency and location.
A model using the Davos geometry including the changing lake level as input parameter was designed to reproduce the ochsohypsen pattern observed in the data. Under the assumption of a flat lake surface without disturbances and a specular reflection on the lake surface, where the reflection angle is equal to the incidence angle, the data was modeled. The spatial distribution of the ochsohypsen was well reconstructed by the model. The temporal evolution of the phase measured on a corner reflector in the target area was also modeled and reflects the measured values well.
The presented work proves that multipath interferences lead to the observed ochsohypsen. This phenomenon is a risk to all ground-based radar campaigns in an upward looking geometry and has to be taken into account when designing a campaign, as the ochsohypsen may overprint all relevant data.
[Authors] [ Overview programme] [ Keywords]
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Paper 165 - Session title: Poster Session 1
Tuesday-139 - Three-dimensional deformation of Coyote dam by the Calaveras fault obtained from multi-aspect Ku-band terrestrial radar interferometry
Werner, Charles (1); Baker, Brett (2); Cassotto, Ryan (3); Wegmüller, Urs (1); Fahnestock, Mark (4) 1: Gamma Remote Sensing, Switzerland; 2: Santa Clara Valley Water District, San Jose, California USA; 3: University of New Hampshire, Department of Earth Sciences; 4: University of Alaska, Fairbanks
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We present three-dimensional deformation time-series of data collected at Coyote Dam near Gilroy California. The Calaveras fault passes directly through the dam and is creeping at a rate of 10 to 15 mm/year. Assessment of deformation in the earthen dam structure is essential for evaluation of safety and planning a possible dam retrofit. The Santa Clara Valley Water District initiated a measurement campaign using the GPRI-II Ku-Band terrestrial radar interferometer during February 2015until July 2015 that measured the line of sight (LOS) deformation at both the upstream and downstream dam faces with millimeter accuracy [1]. The GPRI-II FMCW radar operates at a frequency of 17.2 GHz with a range resolution of 0.9 meters and an azimuth resolution varying between 1 and 2 meters over the dam face [2][3]. Upstream deformation data clearly delineated the fault trace passing through the dam, however the LOS deformation measurements on the downstream face were difficult to reconcile with the current model of the fault motion.
We proposed a second campaign to obtain a series of GPRI measurements from multiple aspects to evaluate the three-dimensional deformation time-series. Data were acquired at intervals of 2 to 4 weeks from 4 locations surrounding the downstream dam face beginning in May 2016 continuing until November 2016. A stable concrete pillar, approximately 1 meter in height, was installed at each observation position allowing the radar to be accurately repositioned within 1-2 mm. The surface of the dam is covered with large boulders ideally suited for long-term interferometric observations. A network of 19 radar reflectors, (both corner and flat-plate) were deployed over the downstream dam face and on the adjacent hillside to facilitate accurate terrain geocoding of the scenes and to provide high-SNR phase measurements at accurately known positions. Data were processed to single-look complex (SLCs) imagesin polar format, with slant range and azimuth angle coordinates. Detected intensity images derived from the SLCs were terrain geocoded using a DEM with 25 cm grid posting acquired with an airborne LIDAR. Each of the measurement positions and the radar reflectors were accurately surveyed. Three of the measurement positions were located along the crest of the dam looking onto the downstream face, and the fourthposition was near the dam outlet looking upstream towards the dam crest. The corner reflectors were especially useful for confirming co-registration of the images acquired from the different viewpoints.
A common phase reference point was established with multiple reflectors pointing at the different measurement locations. A common reference point was selected in an area believed to be stable and clearly visible from all four observation locations. For each epoch, approximately 24 images were acquired and stacked (averaged) to improve both SNR and coherence and to suppress local atmospheric variations. The phase at the reference point was subtracted from each SLC prior to stacking, thereby setting the atmosphere and deformation at the reference point to zero.Interferograms were calculated from the stacked SLC images. Further processing includedadaptive filtering, phase unwrapping using minimum cost flow optimization, and application of a mask to retain only areas with reliable phase. Atmospheric related phase trends were modeled using a linear fit of the interferometric unwrapped phase in a polygonalregion known to be stable. This phase model is subtracted from the interferogram phase and any residual phase offset at the reference point is also removed.
After terrain geocoding, each point in the radar image can be assigned a latitude and longitude in the scene. Given this information and the known location of the radar instrument, the look vector for each point can be calculated in East/North/Up (ENU) coordinates. The deformation time-series for each point can be solved using either least-squares estimation from a large number of short-term interferograms or by simple summation of the unwrapped phases obtained from adjacent image pairs in the acquisition sequence. In this first analysis the latter approach was chosen. One issue is that the observations were acquired at different dates at each of the locations. The time-series from each point is interpolated to a common set of dates. These data are then used to solve for the three-dimensional deformation in ENU coordinates using least-squares (LS) estimation. The solution is implemented using singular value decomposition (SVD) to ensure numerical stability. To obtain a solution for a particular date, at least 3 of the 4 observations must have unwrapped phase values.The observation positions were chosen to be non-coplanar to permit getting a meaningful three-dimensional solution. The unwrapped phase observation data can be weighted in the LS solution by the phase variance derived from the estimated spatial interferometric correlation coefficient.
Terrestrial radar interferometry (TRI) has been demonstrated at Coyote Dam to be a useful technique for measurement of slow tectonic deformation time-series in three dimensions with millimeter accuracy. Advantages of terrestrial interferometry include the ease of implementing observation from multiple aspect angles, near zero baseline for repeat interferometric measurements, and the ability to acquire temporally dense sampling for tracking rapid motion and mitigation of transient atmospheric phase noise.
[1]B. Baker, R. Cassotto, M. Fahnestock, C. Werner, M. Boettcher, Measurement of Creep on the Calaveras Fault at Coyote Dam using Terrestrial Radar Interferometry (TRI). AGU Fall Meeting 2015, retrieved from https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/75970 .
[2] Werner, Charles, A. Wiesmann, T. Strozzi, A. Kos, R. Caduff, and U. Wegmüller (2012), “The GPRI multi-mode differential interferometric radar for ground-based observations”, 9th European Conference on Synthetic Aperture Radar, EUSAR, 23–26 April, Nuremberg, Germany.
[3] Caduff, Rafael, et al. “A review of terrestrial radar interferometry for measuring surface change in the geosciences”, Earth Surf. Process. Landforms 40, 208–228 (2015)
[Authors] [ Overview programme] [ Keywords]
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Paper 169 - Session title: Poster Session 1
Tuesday-10 - Using InSAR water vapour measurements to improve three-dimensional water vapour distribution in GNSS tomographic processing
Benevides, Pedro (1); Catalão, João (1); Nico, Giovanni (2); MA Miranda, Pedro (1) 1: IDL, Universidade Lisboa, Portugal; 2: Istituto per le applicazioni del calcolo “Mauro Picone”, Via Amendola 122/I, 70121 Bari, Italy
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In this study a set of experiments are performed to evaluate the inclusion of high-resolution water vapour measurements provided by an Interferometric SAR (InSAR) acquisition in a GNSS (Global Navigation Satellite System) tomography schema for estimating the three-dimensional water vapour content on the local troposphere. A unique field experiment was performed in Lisbon, Portugal, where a set of GNSS receivers were temporally installed duplicating the total number of stations in the GNSS regional network and an intensive radiosonde launching campaign was carried out for validating the results. It is expected that both the inclusion of InSAR external measurements and the densification of GNSS network will improve the global quality of the three-dimensional water vapour state obtained from the GNSS tomography.
One of the greatest advantages of using space-borne GNSS and SAR sensors to measure the water vapour state is their microwave signal proprieties, which are suitable in all weather conditions and independent from daylight. Interferometric SAR space-borne technique can provide integrated water vapour measurements with a level of precision close to the classical meteorological sensors (e.g. radiosonde). The large footprint area of the SAR acquisitions (hundreds of km2) combined with its high resolution in the order of a few meters, allows to generate a large number of differential water vapour measurements along the radar line-of-sight, with a temporal sampling that is dependent from the sensor revisiting cycle. These differential measurements are the difference of the water vapour state captured at the time instant of each SAR acquisition. GNSS sensors installed on the ground provide precise and continuous water vapour measurements at zenith direction, being a reasonable low cost solution for atmospheric water vapour sensing. However, both techniques alone cannot provide a vertical quantification of the water vapour content along the troposphere and consequently its three-dimensional characterization.
The application of the GNSS water vapour tomography technique can generate a three-dimensional water vapour map over a region within a network of receivers. For that, the local troposphere must be discretized by dividing the space into voxels (volumetric pixels), forming a three-dimensional grid with a typical horizontal and vertical resolution of a few kilometres and hundreds of meters, respectively. The reconstruction of the slant path delay observations results in several ray paths in the satellite line-of-sight at each instant. These observations are mapped into each voxel of the tomographic grid. The relation between the ray traced GNSS signals and the distance travelled inside each voxel allows to estimate the mean water vapour content in all voxels. This poses a typical geophysical inverse problem that can be solved by adopting a damped least-square system of equations. Inverting the system of equations that relates the observations with the grid model spacing results in the estimation of a three-dimensional water vapour map. The non-optimum GNSS observation geometry for the tomography technique, based on an inverted cone centred in the GNSS station on the ground, results in a lack of low angle slant ray paths which affect the grid filling particularly on the lower levels. This implies the need for the introduction of numerical constraints, like averaging between voxels neighbours or limiting the water vapour content by height following a standard atmospheric profile.
In order to include InSAR differential measurements in the GNSS tomography, the processing scheme has to be modified to account for the interferogram temporal baseline, representing the water vapour changes occurred between master and slave image acquisition times. Nevertheless, the higher spatial pixel resolution of the InSAR compared with a GNSS network composed by a few tens of stations at best will result in a significant increment of water vapour observations, and consequently improve the quality of the three-dimensional tomographic water vapour maps (better voxel precision and spatial resolution).
An experiment including interferometric ENVISAT data in the GNSS tomography processing network in the Lisbon region has already provided better water vapour results (Benevides et al., 2016). With the densification of the GNSS network even better results are foreseen for the GNSS tomography with the inclusion of InSAR data. A total of 8 receivers were temporally installed in the region of Lisbon during the month of July 2013, in addition to the 8 stations of the regional GNSS permanent network, doubling the total number of stations in the area. All the GNSS stations are located within the tomographic grid region, with an area of about 60 x 60 km2, being composed by a horizontal resolution of 5 voxels in the longitudinal direction and 6 voxels in the latitudinal direction (see Figure 1). The locations of the temporary stations were chosen in order to reduce the empty voxels of the grid configured by the original GNSS permanent network. Two TerraSAR-X images were acquired over the tomographic grid area, at days 12 and 23 of July 2013 (during the GNSS densification campaign), being generated one interferogram with a small temporal baseline of 11 days. With this very small temporal period it is excepted that the interferometric map reflects mainly the regional atmospheric proprieties. A radiosonde launching campaign performed over the region of study, with a time sampling of 4 hours, enables the validation of the three-dimensional water vapour maps generated by the GNSS tomography with the inclusion of InSAR data. Comparisons between the tomography solution with the permanent network and densified network, with or without the introduction of InSAR data, can be assessed.
The results of the experiment show that InSAR data can provide information to fill the tomographic grid more homogeneously, resulting in a water vapour solution closer to the real atmosphere state, e.g. even capable of resolving dry or wet air intrusions commonly represented in the radiosonde vertical profiles at the lower tropospheric heights (see Figure 2). The availability of other SAR sensors, like Sentinel-1 and ALOS-2 and other possible SAR missions in the near future, can led to a chain production of interferograms with a shorter temporal interval, which will allow to produce regularly three-dimensional water vapour maps of the troposphere applying the technique presented by this work. The inclusion of this water vapour information on the NWP has the potential to improve the weather forecasts.
This work was supported in part by the Portuguese Science Foundation (FCT) under Grant SFRH/BD/80288/2011 and Project SMOG PTDC/CTE-ATM/119922/2010.
Benevides, P., Nico, G., Catalão, J., & Miranda, P. M. A. (2016). Bridging InSAR and GPS Tomography: A New Differential Geometrical Constraint. IEEE Transactions on Geoscience and Remote Sensing, 54(2), 697-702.
[Authors] [ Overview programme] [ Keywords]
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Paper 170 - Session title: Poster Session 1
Tuesday-23 - Comparison Of Earthquake Source Complexity Inferred From Geodetic Surface Displacement Data And Seismological Waveforms
Steinberg, Andreas (1); Sudhaus, Henriette (1); Heimann, Sebastian (2); Isken, Marius (1); Krüger, Frank (3) 1: Kiel University, Institute of Geosciences Kiel, Germany; 2: GFZ, German Research Center for Geosciences, Potsdam, Germany; 3: University of Potsdam, Institute of Earth and Environmental Sciences, Potsdam, Germany
Show abstract
Earthquake rupture processes occur with different degrees of complexity in terms of source segmentation into a discernible number of sub-sources. These sub-sources can be oriented at an angle and/or contribute differently to the total moment release. Source segmentation is often evident for earthquakes with large moment magnitudes (Mw > 7) but also earthquakes in the medium range of moment magnitudes (Mw 5.5-7.0) can be segmented. If source segmentation is apparent, single-source models may not represent the rupture process well. Then the modeling needs to be adjusted to account for a higher complexity through an increased number of model parameters. Often, the apparent degree of source complexity and an Occam's Razor fulfilling solution is estimated intuitively from the observables, for example by judging the surface displacement pattern in InSAR data or from mapped fault data. We seek more objective ways based on the data sensitivity.
We study here the effect of kinematic source model segmentation on the improvement of modeled data fit and on the model parameter dependencies estimated from far-field and near-field observations separately. Near-field observations are static surface displacements derived with Interferometric Synthetic Aperture Radar (InSAR) data from Envisat and Sentinel-1A/B satellites and far-field observations used here are teleseismic waveform data (from 20 to 50 Hz). Potentially, the different sensitivity of near-field and far-field data to earthquake source segmentation matters in joint optimizations of InSAR surface displacements and seismic waveforms.
For our analysis we use real-earthquake data from Central Italy and the Xizang Region (Tibet) and we selected two earthquakes in each region with similar magnitude and normal-faulting mechanisms. The two different regions are chosen to include different seismological station distributions and in this way check for reproducibility of the inferences, while keeping the source characteristics as comparable as possible. In each region we use pairs of earthquakes that are closely located to avoid influences of path effects in the source complexity sensitivity analysis.
The earthquake source models are optimized by using far-field and near-field displacement data separately. To predict near-field static surface displacements we employ rectangular dislocation models embedded in an elastic half-space, with the free source model parameters location (N,E), depth, strike, dip, rake, dip-slip and strike-slip. The forward model formulations to predict far-field seismological waveforms are the commonly used Double-Couples (DC), for which the free source model parameters are location (N,E), depth, time, strike, dip, rake and moment magnitude. The rectangular dislocations are only constrained to not overlap. For multiple DC sub-sources we further consider a Δ parameter (e.g Δlocation).
The source optimization schemes for both near- and far-field observations are harmonized by applying the seismological software toolbox pyrocko (http://pyrocko.org). We consider data errors that are correlated in time and space for seismic waveforms and static surface displacement data, respectively, and propagate them in the estimation of source model parameter trade-offs and uncertainties. To infer the rupture segmentation we explore the data-dependent resolvability by applying informational theory in the form of the Akaike Informational Criterion (AIC) and consult the trade-offs of the estimated source model parameters. We further use array beam-forming of long-period seismic waveforms and seismic back-projections to aid the determination of rupture segmentation. The array beam-forming is an additional model-independent tool to analyze the moment release in time.
In Central Italy we look at the April 06, 2009 L'Aquila earthquake (Mw 6.3), in comparison to the more recent August 24, 2016 (Mw 6.2), earthquake near the town of Amatrice. Previous studies claim that the Amatrice earthquake is associated with a larger source complexity in comparison to the L'Aquila earthquake. In our study the employed AIC confirms for both far- and near-field data that the L'Aquila earthquake can be described adequately with a single-segment source model. In contrast, for the Amatrice earthquake the AIC analysis of the far-field data analysis shows a slight preference for a double DC source and the near-field data AIC analysis shows a clear preference of a two-segments source, supporting the earlier findings. Also the complex appearance of the moment release function for the 2016 Amatrice earthquake points to source segmentation.
In the Xizang area in Tibet we study the April 7, 2005 (Mw 6.2), earthquake and the 40 km to the NW laying August 25, 2008 Zhongba earthquake (Mw 6.7). The AIC favors for both far- and near-field observations of the 2005 earthquake a non-segmented source model and for the 2008 earthquake a more complex two-fault model solution. This is also supported by the function of moment release with time gained through array beam-forming.
From our results so far we conclude that AIC in combination with analysis of source model parameter trade-offs and uncertainties and taking into account moment release functions is a data-driven and objective way to estimate the degree of source model segmentation. It supports finding a meaningful source model parameterization for far- and near-field observations. This is particularly interesting for future joined-data and/or automated earthquake source analyses.
This work is conducted within the project “Bridging Geodesy and Seismology” (www.bridges.uni-kiel.de) funded by the German Research Foundation DFG through an Emmy-Noether grant.
[Authors] [ Overview programme] [ Keywords]
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Paper 174 - Session title: Poster Session 1
Tuesday-53 - New Insight On The Geometry Of Rupture Surfaces Of The Olyutorsk Mw=7.6 April 20, 2006 Earthquake And Its Two Main Aftershocks From SAR Interferometry
Mikhailov, Valentin (1); Kiseleva, Elena (1); Arora, Kusumita (2); Smolianinova, Ekaterina (1); Smirnov, Vladimir (1,3) 1: Schmidt institute of physics of the Earth RAS, Russian Federation; 2: National Geophysical Research Institute, Hyderabad-500007, India; 3: Lomonosov Moscow state University Moscow Russia
Show abstract
The Olyutorsk earthquake of Mw=7.6 occurred in Kamchatka region (Russia) on April 20, 2006. The region is complicated for SAR interferometry as being situated above 600 North latitude it has snow cover during most of the time, mountain topography, strong vegetation etc. We processed 35 ERS-2 images and 6 ENVISAT images and revealed two reliable interferograms covering the main seismic event and two its strongest aftershocks of Mw=6.6.
The first is ERS-2 track 431 interferogram 19.10.2005 -11.07.2007 which covers the period of the main event and Mw=6.6 aftershock on 29.04.2006. Displacement field from the Olyutorsk earthquake can be seen in the central part of the interferogram while the aftershock is in the SE corner. To construct the fault plane model we used data available from geology and seismology and results of postseismic field investigation. Based on geometry of the main thrust zones of the area and spatial distribution of numerous aftershocks we have chosen USGS CMT nodal plane with strike-dip-rake 42-47-100 as a starting model. The final model strike is 500, dip 300 and rake varying from 1620 to 1740 at NE to 32.40 in SW. The estimated total energy is 3.2х1020 N.m compared to 2.8-3.0х1020 from the USGS solution. Postseismic field investigation also revealed thrusts with right-lateral slip. The best fit of the LOS displacements for the aftershock of 29/04/2006 was modeled with strike and dip 2360 and 560 correspondingly, just like in the in the CMT solution of the USGS.
The second interferogram is the ENVISAT 202D track pair 01.05.2006 - 05.06.2006. It covers the strong aftershock of 22 May 2006 Mw=6.6. Fault plane parameters obtained by the inversion of the LOS displacements are: strike 3230, dip 650, rake from 1400 to 1800 (compared to the USGS 340-85-160). Upper and lower edge depth is 1.1 and 12 km. The total energy is 8.0х1018 N m, precisely the same as the USGS estimate.
The area of the earthquake has a bowl-like structure formed by two major thrust zones dipping towards each other. Thrust zone at the NW dips to the SE and the SE one dips to the NW. The aftershock of 29 April 2006 ruptured the SE thrust zone. Area of NW thrust was not investigated but ruptures at the day surface were mapped in the valley of Vyvenka river 30-40 km to the SE from the NW thrust zone. Nevertheless, interferogram covering the period of the Olyutorsk event shows that displacement field extends far to the NW from the ruptures exposed at the surface. The fault surface geometry constructed by inversion of LOS displacements showed that the main thrust zone situated at the NW was also ruptured and the aftershock of 22 May 2006 jointed these two zones.
Hence, constructed for the first time DInSAR based models of the rupture surfaces of the Olyutorsk earthquake and its two main aftershocks provided new constrains on geodynamics of the Northern Kamchatka seismogenic zone.
This study was supported by Russian Science Foundation grant № 16-47-02003 and INT/RUS/RSF/P-13 grant from Department of Science and Technology of Indian Government.
[Authors] [ Overview programme] [ Keywords]
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Paper 177 - Session title: Poster Session 1
Tuesday-82 - Mapping Atmosphere’s Precipitable Water Vapour By InSAR: Geostationary and Geosynchronus vs. Sunsynchronus SAR Acquisitions
Nico, Giovanni (1); Mateus, Pedro (2); Catalao, Joao (2); Soares, Fernando (2) 1: Consiglio Nazionale delle Ricerche (CNR), Istituto per le Applicazioni del Calcolo (IAC), Italy; 2: Universidade de Lisboa, Instituto Dom Luiz, Portugal
Show abstract
The current sun-synchronous SAR configurations have demonstrated their capability to map the atmosphere’s Precipitable Water Vapor (PWV). The recent Sentinel-1 SAR mission is characterized by a revisiting time of six days which means that a time series of SAR images acquired with the same orbit parameters can sample the PWV properties every six days. However, time series of the same regional area can be acquired with along different orbits, both ascending and descending. The merging of PWV maps obtained by independently processing these time series can reduce the temporal sampling of PWV over a given region to 1 to 2 days depending on the extension of the region. Furthermore, the TopSAR acquisition mode of Sentinel-1 mission provides a regional coverage of the SAR images. During the SAR acquisition, the atmosphere can be considered frozen. If PWV maps over the same region, generated by different missions, are merged the temporal sampling of PWV can in principle be reduced to one day. In this work we show the PWV maps which have been obtained over the Iberian Peninsula The spatial resolution of those maps depends on the SAR mission (e.g. the frequency band) but in any case is in the order of a few tens of meters. Assimilation of those maps in a Numerical Weather Model has shown a great advantage with the respect of PWV measurement estimated by GNSS receivers mainly due to their poor spatial resolution.
One of the problems of the sun-synchronous SAR mission is that the updating frequency of PWV is related to their revisiting times which are in the order of days. Above, we mentioned about possible solutions to overcome this problem and this provide a new PWV regional maps every 1 or 2 days. Another possible answer to this problem can be provided by new concepts of geosynchronous and geostationary SAR missions.
Such quasi-continuous imaging capability is a unique feature of both geosynchronous and geostationary SAR, which enables a wide variety of applications, some unprecedented, such as the estimation of water vapor maps at fine resolution on land for Numerical Weather Prediction,
The questions we try to reply in this work are: Can those proposed SAR acquisition modes be really useful for mapping atmosphere PWV? Are they adding more information with respect to that provided by the current network of permanent GNSS receivers? Is it more effective to slightly increase the density of current GNSS networks.
In this work, we show the first regional maps of PWV obtained by Sentinel-1 SAR data over the Iberian Peninsula. Furthermore, we study the problem of assimilating PWV measurements as provided by GNSS stations and Sentinel-1 in a Numerical Weather Model. The result of the assimilation of the PWV measurements with the characteristics of spatial resolution and temporal sampling that would have if provided by geo-stationary / geosynchronous systems are also shown.
The aim of this work is to study, from the point of view of atmosphere scientists, the advantages/disadvantages that PWV maps, provided by Sentinel-1, have with respect to GNSS and the advantages/disadvantages that geo-stationary / geosynchronous SAR could have with respect to both sunsynchronous SAR and GNSS systems.
References:
[1] P. Mateus, R. Tomé, G. Nico, and J. Catalão, “Three-Dimensional Variational Assimilation of InSAR PWV Using the WRFDA Model,” IEEE Transactions on Geoscience and Remote Sensing, vol. 54, no. 12, pp. 7323–7330, 2016.
[2] P. Mateus, J. Catalão, and G. Nico, “Sentinel-1 interferometric SAR mapping of Precipitable Water Vapor over a country-spanning area”, IEEE Transactions on Geoscience and Remote Sensing (submitted).
[3] A. Monti Guarnieri, A. Broquetas, A. Recchia, F. Rocca, J. Ruiz-Rodon, “Advanced radar geosynchronous observation systems: ARGOS”, IEEE Geoscience and Remote Sensing Letters, 12(7), 1406-1410, 2015.
[Authors] [ Overview programme] [ Keywords]
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Paper 179 - Session title: Poster Session 1
Tuesday-8 - SAR Imaging Geodesy– Recent Results for TerraSAR-X and for Sentinel-1
Eineder, Michael (1); Gisinger, Christoph (2); Balss, Ulrich (1); Cong, Xiaoying (2); Montazeri, Sina (1); Hackel, Stefan (1); Rodriguez Gonzalez, Fernando (1); Runge, Hartmut (1) 1: German Aerospace Center (DLR), Germany; 2: Technische Universität München
Show abstract
The Imaging Geodesy or Geodetic SAR technology exploits precise instrument metrology, wave propagation correction and dynamic Earth corrections following geodetic standards, e.g. solid Earth tides, to achieve an absolute pixel positioning accuracy comparable with GNSS [1]. The achievable accuracy is in the low centimeter range, depending on the SAR system resolution, its metrology products such as orbit position and timing, on the SAR processor accuracy and on the accuracy of atmospheric information describing the neutral and dispersive path delay contributions.
In the past the authors have demonstrated absolute positioning of corner reflectors with 5 cm accuracy in 3D space [2] and the positioning of natural points with a about 10 cm accuracy [3,5]. They have furthermore developed a pre-operational processor to add geodetic information to TerraSAR-X products [3]. An extension to other sensors is foreseen, especially Sentinel-1. Moreover, a large corner reflector (CR) array with more than 40 CRs distributed across some 150 by 150 kilometers has become available [4]. It is maintained by Geoscience Australia (GSA) and offers many possibilities in testing and verifying the said methods.
Current work is focused on using alternative reflectors than conventional corner reflectors, exploiting the lower resolution TOPS mode of Sentinel-1 and to seek for more applications of this new geodetic method [5], [6].
The talk summarizes recent developments, i.e.
- highly accurate TerraSAR-X geodetic measurements
- experiences with new, higher resolution ECMWF data to model the neutral atmosphere
- experiences with Sentinel-1 data on the team’s and the GSA corner reflector networks and
- a study plan to extend the technology to Sentinel-1 data
References:
[1] Eineder, Michael und Minet, Christian und Steigenberger, Peter und Cong, Xiaoying und Fritz, Thomas (2011) Imaging Geodesy—Toward Centimeter-Level Ranging Accuracy With TerraSAR-X. In: IEEE TGRS 2010.
[2] Gisinger, Christoph und Balss, Ulrich und Pail, Roland und Zhu, Xiao Xiang und Montazeri, Sina und Gernhardt, Stefan und Eineder, Michael (2015) Precise Three-Dimensional Stereo Localization of Corner Reflectors and Persistent Scatterers With TerraSAR-X. In: IEEE TGRS 2014.
[3] Eineder, Michael und Balss, Ulrich und Suchandt, Steffen und Gisinger, Christoph und Cong, Xiaoying und Runge, Hartmut (2015) A Definition of Next-Generation SAR Products for Geodetic Applications. In: Proceedings of IEEE IGARSS 2015.
[4] Garthwaite, M. C., Hazelwood, M., Nancarrow, S., Hislop, A. and Dawson J. H. (2015) A regional geodetic network to monitor ground surface response to resource extraction in the northern Surat Basin, Queensland. In: Australian Journal of Earth Sciences, vol. 62, pp. 459-477. DOI: 10.1080/08120099.2015.1040073
[4] Gisinger, Christoph und Eineder, Michael und Gruber, Thomas und Balss, Ulrich (2016) Potential of Geodetic SAR for Positioning and Height Monitoring with TerraSAR-X and Sentinel-1. Presentation at ESA Living Planet Symposium 2016, 9.-13. Mai 2016, Prague
[5] Balss, Ulrich und Runge, Hartmut und Suchandt, Steffen und Cong, Xiaoying (2016) Automated Extraction of 3-D Ground Control Points from SAR Images - An Upcoming Novel Data Product. In: IEEE IGARSS 2016.
[Authors] [ Overview programme] [ Keywords]
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Paper 182 - Session title: Poster Session 1
Tuesday-59 - InSAR analysis of 2016 Pedernales, Ecuador Earthquake using Sentinel 1A imagery
Dicelis, Gabriel (1); Assumpcao, Marcelo (1); Kellogg, James (2) 1: University of Sao Paulo, Brazil; 2: 2. University of South Carolina, Andean Geophysical Laboratory (AGL)
Show abstract
On April 16 2016 Ecuador was shaken by the most powerful earthquake of the last 40 years at a depth of 19km, and the fatality count has reached 660 based on United Nations reports (OCHA). The epicenter was centered approximately 27km from the towns of Muisne and Pedernales and 170km from the capital Quito. The mainshock registered magnitude of 7.8Mw and was followed by subsequent aftershocks that reached 6.1-6.2 magnitude ~25km west of Muisne around 3:30am local time.
During earthquakes the earth’s surface is deformed; synthetic aperture radar interferograms (InSAR) technology can measure this vertical movement of the crust using two images of the same area taken at different dates, one before the earthquake and the other one after the shock. We used radar images from the ESA Sentinel 1A satellite to compute coseismic interferograms of the April 16 Ecuador earthquake. The first image was taken on 29 March 2016 before the earthquake and the second one on 24 April after the earthquake had occurred, both in descending orbit wide swath mode. This mode images in three sub-swaths using the Terrain Observation with Progressive Scans SAR or TOPSSAR. On the interferogram shown the rainbow-colored fringes, can be similarly interpreted as the elevation contours; the topography is deducted in either image in order to only reveal the elevations changes that were caused by the earthquake. The focal parameters of the earthquake determined by GCMT are consistent with rupture along the plate interface of the convergent plate boundary, where the Nazca Plate is subducting beneath the South American Plate. The megathrust earthquake ruptured approximately the same area as major earthquake that occurred in 1942. In this study we present the preliminary results of the deformation maps and modeling to estimate the slip distribution of the mainshock. The data include InSAR ascending and descending orbits.
[Authors] [ Overview programme] [ Keywords]
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Paper 185 - Session title: Poster Session 1
Tuesday-116 - Tomographic Profiling Of Snow: Time Series And In-Situ Measurements Within The Scope Of The ESA SnowLab Campaign 2016/2017
Frey, Othmar (1); Werner, Charles (2); Caduff, Rafael (2); Wiesmann, Andreas (2) 1: Gamma Remote Sensing / ETH Zurich, Switzerland; 2: Gamma Remote Sensing
Show abstract
SnowScat is a terrestrial stepped-frequency continuous-wave (SFCW) scatterometer which supports fully-polarimetric measurements within a frequency band from 9.2 to 17.8 GHz [1][2]. Designed originally to support the investigation and validation of snow water equivalent (SWE) retrieval algorithms in the context of the CoReH20 candidate Earth Explorer 7 mission the SnowScat hardware has meanwhile been enhanced by adding a tomographic profiling mode. When operated in tomographic profiling mode the SnowScat device is additionally moved along a rail in elevation direction such that a synthetic aperture can be formed along this dimension. The advantage of this technique is that a high spatial resolution is obtained not only in direction of propagation but also along elevation by employing adequate signal processing techniques. In such a way, high-resolution two-dimensional vertical profiles of a snowpack can be obtained. More specifically, using the SnowScat device in tomographic profiling mode, it is possible to non-destructively retrieve high-resolution information on the spatial variation of radar backscatter, co-polar phase difference, interferometric phase and coherence; observables that (potentially) vary with spatially and temporally changing properties of the snowpack.
The measurement setup and mode of operation of SnowScat in tomographic profiling mode can be briefly described as follows:
The SnowScat device is attached to a rail tilted by 45 degree with a maximal total synthetic aperture length of approx. 2.2m in direction perpendicular to the average line-of-sight pointing direction.
The rail is attached to a scaffolding structure of approx. 10m height. The antenna phase center of the SnowScat device, when positioned at the centre of the synthetic aperture, is then located approximately 7.5m above ground. The radar is pointing in slant range towards the ground/snow and a tomographic test target which is used as a reference and as well as for validation purposes. The test target is made of eight aluminium spheres mounted on a carbon tube.
In winter 2014/2015, a first test campaign at a test site hosted by the WSL Institute for Snow and Avalanche Research (SLF), in Davos, Switzerland was carried out yielding a successful proof of concept of the enhanced hardware, the tomographic measurement, and a basic processing concept. First comparisons of tomographic profiles with in-situ snow profiles indicated that melt-freeze crusts/ice layers present within the snowpack could be identified [3][4].
This is in accordance with similar findings using akin ground-based radar measurements reported in [5][6][7][8].
As a follow-up to this proof of concept the ESA SnowLab project has been set up to provide an experimental framework to investigate the interaction of microwaves with a snowpack under the varying conditions throughout entire alpine snow seasons.
One aspect within this 3-year project is to acquired and process time series of tomographic profiles - as well as regular SnowScat measurements - at dedicated test sites in the Swiss alps.
In winter 2015/2016, the first campaign took place at the test site Gerstenegg, close to the Grimsel pass, in Switzerland, within which a first time-series of tomographic profiles could be acquired and processed [9] (see also the accompanying pdf file for an overview of the test site, the SnowScat device, and a few data examples). During that campaign, up to three tomographic profiles were acquired per day in at least HH and VV polarization - other acquisitions also in all four polarizations HH-HV-VV-VH.
Using this data set it could be shown that various phenomena can be investigated based on this time series of tomographic profiles, such as using
1) the variation of radar backscatter to locate melt-freeze crusts/horizontal layers within the snow pack, 2) using the co-polar (HH-VV) phase difference to characterize potential anisotropy or changes in anisotropy, and 3) using differential (temporal) coherence between tomographic profiles along the time series to measure changes in the propagation delay; spatially resolved in the 2-D vertical profile.
Examples of 2-D resolved profile plots from the 2015/2016 campaign presented in [9] showed e.g. a gradual change of the relative phase difference between the co-polar channels HH and VV in the uppermost part of a tomographic profile measured with the SnowScat device. A likely cause for this phase variation was a fresh snow layer in that upper part of the snow pack. Another example is the interferometric phase differences between subsequent tomographic acquisitions which indicate that spatially well-resolved patterns of phase differences can be obtained using such a time series of tomographic profiles: in some cases, the interferometric phase values were almost constant along the horizontal direction while they varied layer-wise in the vertical direction, whereas almost no phase variation was observed during the very cold and stable conditions. These first findings confirmed the potential of the tomographic profiling approach to track time-varying horizontal and vertical heterogeneity of a snow pack.
In this contribution, the detailed tomographic profiling measurement and the updated time-domain tomographic focusing concept based on [10] is discussed and, in particular, results from the time series of the new winter campaign 2016/2017 will be shown and compared with in-situ snow measurements (e.g. SnowMicroPen profiles) regularly performed on site by the WSL Snow and Avalanche Research Institute (SLF), in Davos, Switzerland.
The ESA SnowLab campaign and data processing has been conducted in the frame of ESA/ESTEC Contract No. 4000117123/16/NL/FF/MG.
References
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[1] A. Wiesmann, C. L. Werner, C. Matzler, M. Schneebeli, T. Strozzi, and U. Wegmuller, “Mobile X- to Ku-band scatterometer in support of the CoRe-H2O mission,” in Proc. IEEE Int. Geosci. Remote Sens. Symp., vol. 5, July 2008, pp. 244–247.
[2] C. L. Werner, A. Wiesmann, T. Strozzi, M. Schneebeli, and C. Matzler, “The SnowScat ground-based polarimetric scatterometer: Calibration and initial measurements from Davos Switzerland,” in Proc. IEEE Int. Geosci. Remote Sens. Symp., July 2010, pp. 2363–2366.
[3] O. Frey, C. L. Werner, M. Schneebeli, A. Macfarlane, and A. Wiesmann, “Enhancement of SnowScat for tomographic observation capabilities,” in Proc. FRINGE 2015, ser. ESA SP-731, Mar. 2015.
[4] O. Frey, C. L. Werner, and A. Wiesmann, “Tomographic profiling of the structure of a snow pack at X-/Ku-band using SnowScat in SAR mode,” in Proc. EuRAD 2015 - 12th European Radar Conference, Sept. 2015, pp. 21–24. [doi:10.1109/EuRAD.2015.7346227]
[5] S. Tebaldini and L. Ferro-Famil, “High resolution three-dimensional imaging of a snowpack from ground-based SAR data acquired at X and Ku band,” in Proc. IEEE Int. Geosci. Remote Sens. Symp., July 2013, pp. 77–80.
[6] L. Ferro-Famil, S. Tebaldini, M. Davy, and F. Boute, “3D SAR imaging of the snowpack at X- and Ku-band: results from the AlpSAR campaign,” in Proc. of EUSAR 2014 - 10th European Conference on Synthetic Aperture Radar, June 2014, pp. 1–4.
[7] K. Morrison and J. Bennett, “Tomographic profiling - a technique for multi-incidence-angle retrieval of the vertical SAR backscattering profiles of biogeophysical targets,” IEEE Trans. Geosci. Remote Sens., vol. 52, no. 2, pp. 1350–1355, Feb. 2014.
[8] B. Rekioua, M. Davy, and L. Ferro-Famil, “Snowpack characterization using SAR tomography - experimental results of the AlpSAR campaign,” in Radar Conference (EuRAD), 2015 European, Sept 2015, pp. 33–36.
[9] O. Frey, C. L. Werner, R. Caduff, and A. Wiesmann, “A time series of tomographic profiles of a snow pack measured with SnowScat at X-/Ku-Band,” in Proc. IEEE Int. Geosci. Remote Sens. Symp., vol. 1, pp. 17-20, July 2016. [doi:10.1109/IGARSS.2016.7728995]
[10] O. Frey and E. Meier, “3-D time-domain SAR imaging of a forest using airborne multibaseline data at L- and P-bands,” IEEE Trans. Geosci. Remote Sens., vol. 49, no. 10, pp. 3660–3664, Oct. 2011.
[Authors] [ Overview programme] [ Keywords]
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Paper 186 - Session title: Poster Session 1
Tuesday-125 - Cloud storage and computing resources for the UNAVCO SAR Archive
Baker, Scott; Crosby, Christopher; Meertens, Charles UNAVCO, United States of America
Show abstract
UNAVCO is a non-profit university-governed consortium that operates the National Science Foundation (NSF) Geodesy Advancing Geosciences and EarthScope (GAGE) facility and provides operational support to the Western North America InSAR Consortium (WInSAR). The synthetic aperture radar (SAR) archive at UNAVCO currently provides access to over 80TB of unprocessed data for community geoscience research. Historically, users have downloaded data and performed InSAR processing on local machines. However, given the increasing volumes of SAR data available and the size of an individual scene, this model may be inefficient. As cloud computing has become more mainstream, UNAVCO has begun developing capabilities to provide data and processing resources in the same location. The test environment is using the Texas Advanced Computing Center (TACC), part of the NSF Extreme Science and Engineering Discovery Environment (XSEDE). The entire UNAVCO SAR archive is available at TACC along with virtual machines preconfigured with InSAR processing software. Users can quickly access and process SAR data at the TACC, providing a scalable computing environment for more efficient and larger scale analyses by the UNAVCO WInSAR community.
[Authors] [ Overview programme] [ Keywords]
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Paper 189 - Session title: Poster Session 1
Tuesday-24 - Assessing Vertical Elevation Changes of Coastal Areas in Southern Chile to Improve The Understanding of Their Paleotsunami Sedimentary Records
Wils, Katleen (1); Walstra, Jan (2); Heyvaert, Vanessa (2,1); De Batist, Marc (1) 1: Renard Centre of Marine Geology (RCMG), Department of Geology, Ghent University, Gent, Belgium; 2: Geological Survey of Belgium, Royal Belgian Institute of Natural Sciences, Brussels, Belgium
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Determining the recurrence rate in time and space of ruptures along megathrust segments of a subduction zone and associated tsunamis is essential in performing hazard assessment. Without this type of information, it is impossible to perform adequate risk assessments for future megathrust earthquakes and the possible subsequent tsunamis which can impact (highly) populated areas such as the Chilean coastal areas (e.g. the 2010 Maule earthquake and tsunami). Given that the typical duration of an entire seismic cycle is in the order of several hundreds of years, it is not possible to obtain this type of data from instrumental or even historical records but it requires the study of geological records. For the study of paleotsunamis, usually records from coastal lowlands and estuaries are used. This has recently been extended to coastal lakes as well. The sedimentary record provided by these coastal lowlands and lakes is mainly interpreted assuming that the vertical level of the considered location has been stable over short time intervals (years or decades) or even longer timescales of one or more seismic cycles. This is however a strong simplification and rarely the case as a consequence of the dynamics associated with subduction zones.
A megathrust segment of a subduction zone can be locked and the location and depth of locking determines the patterns, amounts and rates of elastic deformations occurring in the overriding plate. This results in interseismic uplift and/or subsidence, followed by relaxation during an earthquake event, thus affecting the connectivity and depositional environment in coastal lakes (e.g. significant subsidence can at a given point allow for lakes to be inundated by a tsunami wave). The aim of this research is to obtain a better insight in the influence of the vertical component of interseismic deformation on the recording threshold and recording stability of coastal lakes, which has been neglected up to now. More specifically, this will be done in the Chilean coastal area surrounding Lago Vichuquén (to the North of Constitución), Lago del Budi, Lagunas Gemelas, Lago Huelde and Lago Cucao (on Chiloe Island) and Aysén fjord. The study area thus comprises the Maule segment, as well as the northern part of the Valdivia segment and the Liquiñe-Ofqui Fault Zone (LOFZ).
To measure tectonic deformation processes with a high precision and spatial coherence over a relatively large geographical area, multi-temporal SAR data will be exploited. Advanced radar interferometry techniques such as PSI will be used to determine spatial and temporal trends in surface elevation changes or ground movement. This allows for very precise measurements of displacements and velocities of individual scatterer points over long time periods, allowing the estimation of interseismic deformation over extensive areas. Interferometry data only provides information on short-term changes in coastal elevation, which is not easy to extrapolate towards the length of an entire seismic cycle. To achieve this, ideally the InSAR data should be combined with more continuous data series (such as those provided by GPS measurements) and long-term geological records.
In the first stage of the project, extensive time series from the ENVISAT, provided by ESA will be processed to obtain the necessary information over the last 10 to 15 years. The focus will lie firstly on the southern part of the study area with the LOFZ and the Valdivia segment of the subduction zone, moving northwards towards the Maule segment. Preliminary results of processing with respect to time series and deformational patterns will be presented. This should already give a first impression on the stability of these coastal areas, showing the order of magnitude of potential uplift or subsidence that is occurring. Later on, processing will be extended to data from ERS and Sentinel-1. Finally, InSAR data will be combined and compared with GPS data according to existing techniques as well as with geomorphological and geological field data. Compilation of all acquired vertical land elevation changes for the different study areas will eventually be used to evaluate the impact of past interseismic deformation on the coastal areas (i.e. coastal lakes).
[Authors] [ Overview programme] [ Keywords]
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Paper 191 - Session title: Poster Session 1
Tuesday-25 - Reassessment of seismic hazards of high strain accumulation in SW Taiwan: Insight from multi-temporal InSAR and numerical simulation
Hu, Jyr-Ching (1); Tung, Hsin (1); Huang, Mong-Han (2); Kuo, Ying-Ping (1); Tan, Eh (3) 1: National Taiwan University, Taiwan, Republic of China; 2: JPL, California Institute of Technology; 3: Institute of Earth Sciences, Academia Sinica
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Rapid strain accommodation and high uplift across the fold-and-thrust belt in SW Taiwan are revealed by the Continuous GPS, precise leveling and SAR interferometry. The previous block model based on GPS measurement suggested a high seismic risk in SW Taiwan. However, a clear evidence of multiple fault slip along a fold-and-thrust belt at 5-10 km depth was triggered by the 2016 Mw Meinong earthquake at 15-20 km depth. The primary coseismic fault slip was deduced with kinematic model based on seismic and geodetic measurements and triggered fault slip along the shallow fold-and-thrust belt was constrained by SAR interferometry. We hypothesize that the surface interseismic deformation is mainly controlled by a structure related to the shallow detachment at around 5-10 km depth, which a proposed duplex in a region of high pressure and high interseismic uplift rate. It is surprising to notice that the footwall of Longchuan reverse fault demonstrates a high uplift rate of ~20-30 mm/yr in interseismic period. This anomalous deformation rate might part be related with a ramp duplex located in the footwall and the triggered slip of moderate earthquake in nearby area by 2010 Jia-Shian and 2016 Meinong earthquakes. In addition, the mechanical heterogeneity of mudstone in the Gutingkang formation might play a crucial role of anomalous deformation. Consequently, we use an Efficient Unstructured Finite Element method (DynearthSol2D) to simulate and discuss the contrast of viscosity in mudstone and sandstone contributed in deformation pattern and upward mobility. We also want to check the previous hypothesis of mud diapirism and incorporate a new mud-cored anticline model for mechanic explanation of anomalous interseismic deformation occurred in SW Taiwan.
[Authors] [ Overview programme] [ Keywords]
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Paper 192 - Session title: Poster Session 1
Tuesday-69 - Detection of mowing events on grasslands with Sentinel-1 interferometry
Zalite, Karlis (1,2,3); Tamm, Tanel (1,2,4); Voormansik, Kaupo (1,2); Koppel, Kalev (1,2,4) 1: Tartu Observatory, Estonia; 2: KappaZeta Ltd, Estonia; 3: Department of Physical Geography and Ecosystem Science, Lund University, Sweden; 4: Department of Geography, University of Tartu, Estonia
Show abstract
Grasslands cover a large proportion of agricultural area in Europe, and their maintenance is supported via the Common Agricultural Policy (CAP). CAP encourages the owners to maintain their grasslands in good agricultural and environmental conditions, and in return they receive subsidy payments. One of the obligations requires the grasslands to be mowed or grazed on a yearly basis. Today, the validation of these management practices is carried out in limited areas and by using visual interpretation of very high resolution satellite images and on-site field inspections. However, use of space borne remote sensing data, namely from the Copernicus Sentinels, would make the validation process more effective. Use of Earth Observation (EO) data would allow the National Paying Agencies (NPA) in charge of validation to perform the checks over a much larger area, leading to a more effective use of resources and helping to reduce the number of false payments.
SAR data provided by the Sentinel-1 satellites is inherently well suited for continuous observations. While optical remote sensing offers mature methods for detecting mowing events, many important agricultural areas are so persistently and pervasively covered by clouds that less than half of their weekly composites would be even 70% clear of cloud cover [1]. Alternatively, SAR signal can penetrate the clouds virtually in all weather conditions providing continuous data covering a large area.
Both PolSAR and InSAR-based approaches have been shown to be potentially suited for the detection of mowing events on grasslands [2,3]. However, the regularity of Sentinel-1 data is well-suited for InSAR applications. Zalite et al. [2] demonstrated how 1-day X-band interferometric coherence is much higher for mowed grasslands when compared to grasslands covered by vegetation.
In this study, interferometric coherence calculated from 12-day Sentinel-1 image pairs were analyzed in relation to mowing events on agricultural grasslands in Estonia [4]. In total, 77 mowing events were used spanning the 2015 vegetative season. The study focused on the impact that temporal separation between a mowing event and interferometric acquisitions has on the coherence values. Additionally, the effect of precipitation on the coherence was analyzed, as it has been shown before that precipitation may hinder the correct interpretation of coherence in relation to mowing events [2]. Two data stacks were analyzed – morning acquisitions from relative orbit number (RON) 80 and afternoon acquisitions from RON160.
Results showed that after a mowing event median VH and VV polarization coherence values were statistically significantly higher than those from before the event. In general, the effect was statistically significant even 24 to 36 days after a mowing event, apart from morning acquisitions. However, the effect was stronger when less time had passed between an event and the first interferometric acquisition. Precipitation caused the coherence to decrease, making the potential detection of mowing events problematic. This was true for rain as well as for morning dew. The increase of coherence after an event should be more pronounced when using interferometric pairs with 6-day temporal baselines, available after the launch of Sentinel-1B satellite. The impact of decreasing the temporal baseline is discussed in this report. In addition, preliminary results from 2016 campaign are discussed as well. In 2016, more events were recorded spanning a wider region and two countries – Estonia and Latvia.
[1] Whitcraft, A.K.; Vermote, E.F.; Becker-Reshef, I.; Justice, C.O. Cloud cover throughout the agricultural growing season: Impacts on passive optical earth observations. Remote Sens. Environ. 2015, 156, 438–447
[2] Zalite, K.; Antropov, O.; Praks, J.; Voormansik, K.; Noorma, M. Monitoring of agricultural grasslands with time series of X-band repeat-pass interferometric SAR. IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens. 2015, 9, 3687–3697
[3] Voormansik, K.; Jagdhuber, T.; Zalite, K.; Noorma, M.; Hajnsek, I. Observations of cutting practices in agricultural grasslands using polarimetric SAR. IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens. 2015, 9, 1382–1396.
[4] Tamm, T.; Zalite, K.; Voormansik, K.; Talgre, L. Relating Sentinel-1 Interferometric Coherence to Mowing Events on Grasslands. Remote Sens. 2016, 8, 802.
[Authors] [ Overview programme] [ Keywords]
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Paper 193 - Session title: Poster Session 1
Tuesday-83 - Identification Of Active Cryoforms In The Central Andes Of Argentina Using SAR Data
Euillades, Leonardo Daniel (1,2); Bernardi, Gustavo Ariel (2,4); Sosa, Gustavo (1,2); Euillades, Pablo Andres (1,2); Capone, Augusto (1); Mieras, Franco (1); Fontana, Pedro (1); Carelli, Maria Fernanda (3,4); Valdez, David (3) 1: Instituto CEDIAC - Facultad de Ingenieria - Universidad Nacional de Cuyo, Mendoza, Argentina; 2: CONICET, Argentina; 3: Instituto Nacional del Agua, División San Juan, San Juan, Argentina; 4: INGEO, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de San Juan, San Juan, Argentina
Show abstract
In the cryosphere of the Central section of the Andes Cordillera, rock and covered glaciers [1] are both inland freshwater resources and good indicators of regional climate variability [2]–[4]. Those landforms, tongue or lobed shaped, are developed near at high mountain slopes within permafrost areas [5]. They represent dynamic systems with varying activity, where rock fragments are mixed with ice in different proportions, consisting in a permanently frozen mixed ice-debris core and a top layer suffering seasonal thawing process ("active layer") [6]–[8]. In this type of systems, the variation in its topography would be motivated by both the seasonal loss and recovery of ice content, and the slope-down gravitational action. Verticals and lateral movements of the detrital surfaces indicate the evolution of the underlying or intrinsic ice mass [9]. In practice, the identification and analysis of some characteristics of these cryoforms can be performed using remote sensing data, being a good complement for the glaciological and/or geomorphological field work.
In this work, we present the progress carried out studying a set of rock glaciers located in the San Juan Province, within the Central Andes of Argentina. The main objective of this work is to identify and characterize the cryoforms present in the area in order to obtain a more comprehensive idea of the dynamics of this type of glaciers and their impact in the Central Andean environment.
Differential SAR Interferometry (DInSAR) is an extensively and suitable tool to provide ground deformation measurements [10]. However, success in high deformation rate areas, like those involving glaciers, depends strongly on the instrument acquisition policy. Missions with short revisit time become mandatory in order to assess the occurred displacements. When large displacements are expected, an alternative is to employ a SAR amplitude signal based technique (i.e. Pixel Offset – PO) [12], [13]. The main drawback of PO is related to its accuracy, what is one order of magnitude worst at least than for DInSAR. Availability of high-resolution SAR systems is an improvement, bringing the precision of the obtained results near to that attainable with DInSAR [14].
Availability of the new ESA SAR mission, Sentinel-1, characterized by a 6-days revisit time, opens a new perspective for studying this kind of environments. The default operation mode, TOPS, that is able to acquire a wide swath of ~250km with interferometric capabilities renders the system an invaluable tool for monitoring wide areas. However, it is important to analyze the capabilities of the system for retrieving the displacements occurred in rock and covered glaciers characterized by a deformation rate between 0.5 to 1 m/y [11], taking into account the spatial resolution of the system.
We analyze an area of interest comprises between (S32.25°;W70.58°) and (S31.76°;W69.97) which includes more than 20 rock and covered glaciers. Methodology has been organized as follow. We analyze a set of differential interferograms computed from 4 COSMO-Skymed HImage SAR ascending and descending datasets (39 acquisitions). Then, a set of Sentinel-1 A/B IW acquisitions have been processed in order to compute a set of differential interferograms. Analysis of the retrieved displacement has been performed in order to classify the rock glaciers according to its current state. This work allowed us to make a first performance evaluation of Sentinel-1 SAR data in glacier environments that present slow to medium deformation rates and compare the obtained results against those computed using a high resolution SAR system.
[1] IANIGLA, “Inventario Nacional de Glaciares y Ambiente Periglacial: Fundamentos y Cronograma de Ejecución.” Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, 2010.
[2] A. Rabatel, H. Castebrunet, V. Favier, L. Nicholson, and C. Kinnard, “Glacier changes in the Pascua-Lama region, Chilean Andes (29° S): recent mass balance and 50 yr surface area variations,” The Cryosphere, vol. 5, no. 4, pp. 1029–1041, Nov. 2011.
[3] G. F. Azócar and A. Brenning, “Hydrological and geomorphological significance of rock glaciers in the dry Andes, Chile (27°-33°S),” Permafr. Periglac. Process., vol. 21, no. 1, pp. 42–53, Jan. 2010.
[4] A. Brenning, “Geomorphological, hydrological and climatic significance of rock glaciers in the Andes of Central Chile (33-35°S),” Permafr. Periglac. Process., vol. 16, no. 3, pp. 231–240, Jul. 2005.
[5] J. P. Milana and A. Güell, “Diferencias mecánicas e hídricas del permafrost en glaciares de rocas glaciánicos y criogénicos, obtenidas de datos sísmicos en El Tapado, Chile,” Rev. Asoc. Geológica Argent., vol. 63, pp. 310 – 325, 2008.
[6] F. A. Croce and J. P. Milana, “Internal structure and behaviour of a rock glacier in the Arid Andes of Argentina,” Permafr. Periglac. Process., vol. 13, no. 4, pp. 289–299, Oct. 2002.
[7] F. Croce and J. P. Milana, “Electrical Tomography applied to image the 3D extent of the permafrost of three different Rock Glaciers of the Arid Andes of Argentina,” in Geophysical Research Abstracts, 2006, vol. 8, p. 03026.
[8] A. Kääb and M. Weber, “Development of transverse ridges on rock glaciers: field measurements and laboratory experiments,” Permafr. Periglac. Process., vol. 15, no. 4, pp. 379–391, Oct. 2004.
[9] L. Liu, C. I. Millar, R. D. Westfall, and H. A. Zebker, “Surface motion of active rock glaciers in the Sierra Nevada, California, USA: inventory and a case study using InSAR,” The Cryosphere, vol. 7, no. 4, pp. 1109–1119, Jul. 2013.
[10] A. K. Gabriel, R. M. Goldstein, and H. A. Zebker, “Mapping small elevation changes over large areas - Differential radar interferometry,” J. Geophys. Res., pp. 9183–919, Jul. 1989.
[11] C. Harris, “The nature and dynamics of mountain permafrost: introduction,” Permafr. Periglac. Process., vol. 15, no. 3, pp. 189–189, Jul. 2004.
[12] T. Strozzi, A. Luckman, T. Murray, U. Wegmuller, and C. L. Werner, “Glacier motion estimation using SAR offset-tracking procedures,” IEEE Trans. Geosci. Remote Sens., vol. 40, no. 11, pp. 2384–2391, Nov. 2002.
[13] F. Casu, A. Manconi, A. Pepe, and R. Lanari, “Deformation Time-Series Generation in Areas Characterized by Large Displacement Dynamics: The SAR Amplitude Pixel-Offset SBAS Technique,” IEEE Trans. Geosci. Remote Sens., vol. 49, no. 7, pp. 2752 –2763, Jul. 2011.
[14] N. Riveros, L. Euillades, P. Euillades, S. Moreiras, and S. Balbarani, “Offset tracking procedure applied to high resolution SAR data on Viedma Glacier, Patagonian Andes, Argentina,” Adv. Geosci., vol. 35, pp. 7–13, Jun. 2013.
[Authors] [ Overview programme] [ Keywords]
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Paper 195 - Session title: Poster Session 1
Tuesday-121 - An Improvement of SAR Offset Tracking Performance Considering Multiple Feature Window Sizes
Chae, Sung-Ho (1); Lee, Won-Jin (2); Jung, Hyung-Sup (1) 1: University of Seoul, Republic of South Korea; 2: Division of Global Environment System Research, National Institute of Meteorological Research, Republic of South Korea
Show abstract
For analyzing the mechanism of surface deformation, synthetic aperture radar (SAR) techniques have been widely used because it has the capabilities of all-weather observation and high spatial resolution. Among the techniques, SAR interferometry (InSAR) has been successfully implemented to observe surface displacements since it enables the precise observations of surface deformation (millimeter-to meter-level deformation) over a large area running to thousands of square kilometers. However, with the InSAR method, it is difficult to precisely measure fast and large scale displacements because the deformation rate exceeds the maximum detectable deformation rate of one fringe. It makes phase unwrapping problems that are due to extreme fringe rates and cause a dominant error in the interferogram. On the contrary, SAR offset tracking method would be a feasible solution in the case of abrupt and large deformation observation because it is not necessary to phase unwrapping procedure. It can provide unambiguous ground displacements in both the line-of-sight (LOS) and azimuth directions. To define relative movements of features, the method uses an intensity cross-correlation method between pairs of SAR images. In the tracking procedure, the feature window fixed in the reference (master) image shifts within the each location of the search (slave) image and calculates the cross-correlation for each window shift to decide the offsets. The measurement performance of the method depends on the existence of identical features in the pairs of images at the scale of the feature window. In high coherence area, because the features of the two images are well correlated, tracking with a small feature window can be performed accurately. On the other hand, in low coherence area, large feature window needs to be utilized for accurate offset tracking. For the reason, this paper proposes an efficient SAR offset tracking method considering multiple feature window sizes. The method exploits an iterative SAR offset tracking with multiple feature window sizes and then calculate a final offset measurement by averaging the offset measurements after removing the outliers. Then, the final LOS and azimuth displacement maps were generated. The performance of this method was tested using European Remote Sensing 2 (ERS-2) SAR data sets that observed the coseismic displacements of the 1999 Hector Mine earthquake event in California. By comparing results from the proposed SAR offset tracking method with displacements from GPS data, the root-mean-square (rms) errors in the LOS and azimuth directions of the displacement are 6.6 and 6.7 cm. Especially in the case of accuracy of the azimuth displacement, it corresponds to 1.3% of the azimuth resolution that is better than the accuracy of 12-15 cm published previously. It is also better than the conventional SAR offset tracking result of 1.6% from the ALOS PALSAR. In addition, according to visual inspection, the results of the proposed method using multiple feature window sizes display markedly diminished filtering artifacts, in comparison to other results using a single kernel window size. In fact, the rupture line is more clearly visible in the results from the proposed method. From these results, it is demonstrated that the proposed method is suitable for accurately measuring the large surface displacements. Moreover, the results suggest further studies to be done in order to implement the qualitative and quantitative assessment for the quality of the displacements maps from the proposed method and apply the method to other distinct events that are the 2011 Kamoamoa fissure eruption and the 2016 Kumamoto Earthquake SAR data and other SAR data acquired from ALOS-2 PALSAR-2 and TerraSAR-X.
[Authors] [ Overview programme] [ Keywords]
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Paper 203 - Session title: Poster Session 1
Tuesday-3 - Mitigation of atmospheric contribution in InSAR time series using global weather models and high resolution local weather models
Varugu, Bhuvan Kumaru; Amelung, Falk University of Miami, United States of America
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Presence of atmospheric component in the InSAR deformation estimates has been limiting the application of the technique to constrain slow displacements such as in volcanoes and fault motions. Particularly, the moist component induced by atmospheric water vapor exhibits a structured variability that confounds detection of surface elevation changes. Use of atmospheric models to calculate path delays has been attempted in past but are significantly affected by the poor resolution of atmospheric model.
In this study we compare InSAR time-series results of the Hawaiian volcanoes using SAR data of the Cosmo-Skymed constellation using a variety of correction approaches: based on (1) global atmospheric weather models, (2) a local 300m resolution Weather model in which delays from GPS are also included. Further, results from UAVSAR acquisitions will be presented to explain the propagation of delay over time.
[Authors] [ Overview programme] [ Keywords]
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Paper 204 - Session title: Poster Session 1
Tuesday-11 - Integration Of GNSS And High Resolution ECMWF For InSAR Atmospheric Corrections Worldwide And At All Times
Yu, Chen (1,2); Li, Zhenhong (1,2); Crippa, Paola (1,2); Penna, Nigel (1) 1: Newcastle University, United Kingdom; 2: Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET), United Kingdom
Show abstract
The recently launched ESA Sentinel-1 satellites (Sentinel-1A on 3 April 2014 and Sentinel-1B on 25 April 2016) carry an advanced C-band radar instrument able to provide an all-weather, day-and-night supply of imagery of the Earth’s surface. As a constellation of two satellites orbiting 180° apart, the Sentinel-1 mission images the entire Earth every six days, thus providing a unique dataset to map the Earth’s surface movements including crustal deformation, arctic sea-ice extent, sea-level, permafrost and glacier changes. It is well known that radar signals are significantly delayed when passing through the atmosphere as a result of water vapour presence. The accuracy of Interferometric Synthetic Aperture Radar (InSAR) retrievals is strongly affected by the spatio-temporal variations of tropospheric water vapour, which can cause errors comparable in magnitude to those associated with crustal deformation. Therefore, mitigating InSAR atmospheric artefacts is essential to infer accurate surface displacements, especially when estimating low-amplitude, long-wavelength deformation fields such as those due to inter-seismic strain accumulation and/or post-seismic motion.
Tropospheric delays, especially the component associated with atmospheric water vapour, vary in space both vertically and horizontally. Several studies have accounted for elevation dependent water vapour delays, however, major challenges still remain to describe the turbulent component. In this work, we develop an Iterative Tropospheric Decomposition (ITD) model that enables us to decouple the total delay into (i) a stratified component highly correlated with topography and (ii) a turbulent component resulting from small scale irregular air motions which is highly variable in space and time. We demonstrate that our ITD model is able to account simultaneously for both tropospheric stratification and turbulence and generates high precision high spatial resolution tropospheric delay maps over both flat and mountainous areas.
We apply the ITD model on Sentinel-1 interferograms with the pointwise high precision and high rate zenith total delay (ZTD) estimates obtained from ground-based Global Navigation Satellite System (GNSS) networks available in all-weather conditions and real-time mode. Due to the lack of a dense GNSS network in some regions of the world, we also utilise the operational high resolution European Centre for Medium-Range Weather Forecasts (HRES-ECMWF, ~16 km) model output, available globally in near real-time with a 6-hour interval. Our results indicate that HRES-ECMWF provides significantly improved tropospheric delay estimates than those generated using the reanalysis ECMWF products from ERA-Interim (~75 km), as evidenced by both GNSS and Moderate Resolution Imaging Spectroradiometer (MODIS) observations. By combining high temporal resolution GNSS ZTDs with HRES-ECMWF ZTD grids, an average of 65% noise reduction was achieved with a maximum of 80%, on a variety of interferograms over a range of topographic and climatic conditions (Central California, South Italy and Southwest England). After correction, InSAR displacements agreed to GPS with RMS differences well below 1 cm in 90% cases. To assess whether the ITD correction is feasible for each interferogram, two performance indicators, namely Cross RMS and Spacing Test, have been developed. These two indicators appear to be effective to identify outliers, strong turbulence effects and weak GNSS network geometries; the first one can also be used to assign proper weights when multi datasets are included in the ITD model.
To summarise, our work demonstrates that the combined use of GNSS and ECMWF in the ITD model allows for accurate and reliable InSAR atmospheric corrections worldwide and at all times, in near real time.
[Authors] [ Overview programme] [ Keywords]
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Paper 209 - Session title: Poster Session 1
Tuesday-129 - Extracting Small and Long-Wavelength Vertical Land Surface Movements from an InSAR Image Time Series: The Case of Glacial Isostatic Adjustment in Scotland
Stockamp, Julia (1); Li, Zhenhong (2) 1: University of Glasgow, United Kingdom; 2: Newcastle University, United Kingdom
Show abstract
When assessing past and future sea level trends at Scotland’s coast, understanding the effects of glacial isostatic adjustment (GIA) plays a crucial role. Especially against the backdrop of climate change and the global rise of sea levels, it is important to adequately determine the modern rate and spatial distribution of GIA-related crustal uplift in Scotland.
Differential SAR Interferometry (D-InSAR) is an established technique for analysing crustal motion and land surface deformation caused by co- and interseismic processes, volcanic activity, landslides and subsidence. However, when it comes to the detection of small, long-wavelength displacements, such as GIA-induced vertical land movement, the application of D-InSAR becomes challenging. A very high quality standard in terms of precision and accuracy is then necessary to make it a competitive tool to established geodetic techniques, such as GNSS.
This study investigates the applicability of a D-InSAR time series technique, the Small Baseline approach (SBAS), in its ability to determine recent rates of vertical land motion in Scotland with a high accuracy and precision (in the mm/yr level), as well as on a broader spatial scale than conventional geodetic techniques that rely on spatial interpolation. A range of error signals (atmospheric water vapour, orbital ramps, topographic artefacts etc.) needs to be sufficiently eliminated before the extraction of any uplift signal is possible. This requires the advancement of correction techniques for such artefacts within the applied time series inversion processing chain. To reduce residual orbit errors in the differential interferograms, an improved network correction technique, that incorporates phase loop triplets of interferograms into the observation equations, has already been established with good results. In addition, further methods are being tested for the separation of the desired deformation signal from atmospheric errors. This comprises the integration of Principal Component Analysis and Undercomplete Independent Component Analysis in the SBAS processing chain in order to take advantage of the signals’ different spatial and temporal characteristics. The idea is to decompose the total image time series into a range of (independent) spatial and temporal basis functions, followed by a reconstruction of the deformation signal by selecting the relevant components, thereby discarding any tropospheric disturbances.
Different SAR satellites and frequencies are used in this investigation in order to cover a time frame of up to 20 years. They include ESA’s ERS-1/2, ESA’s Envisat ASAR, ESA’s Sentinel-1 and JAXA’s ALOS PALSAR.
[Authors] [ Overview programme] [ Keywords]
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Paper 211 - Session title: Poster Session 1
Tuesday-26 - Mapping the distribution of fault creep along northern coastal California faults using InSAR
Swiatlowski, Jerlyn L; Funning, Gareth J University of California, Riverside, United States of America
Show abstract
Fault creep, slow aseismic slip occurring along a fault that is expressed at the surface, is poorly constrained on northern coastal California faults due to the low density of observations along their extents. Creep reduces the fault area capable of rupturing in an earthquake so, by mapping the areas where creep is occurring, we can infer where the fault is locked (not creeping) thus, we can find areas where the fault is accumulating strain for a future earthquake. The Rodgers Creek and Maacama faults both show evidence of fault creep through offset cultural features, (e.g. offset sidewalks and fences), and at alinement arrays placed in locations where creep has been inferred (McFarland et al., 2009). Using the ERS satellites, the distribution of fault creep has been mapped along the Rodgers Creek and Maacama faults from persistent scatterer InSAR (PSI) and estimates of the creep rate are made. We processed a 39 image dataset using the StaMPS PSI code (Hooper et al., 2004), spanning 1992-2000, along the southern Maacama fault and northern Rodgers Creek fault (track 113, frames 2817 & 2835). By creating fault perpendicular profiles through our data, we identify fault creep along the Maacama fault around the cities of Ukiah and Willits. If projected into the fault parallel direction, and assuming pure right-lateral strike-slip motion, the creep rates for Ukiah are 2.6 – 3.2 mm/yr, and 1.8 – 4.3 mm/yr in Willits.
We compare our ERS analysis with preliminary results from Sentinel-1 and ALOS-2. Using the InSAR Scientific Computing Environment (ISCE) software to process the data for both satellites, and a linked-stacking approach we estimate line-of-sight velocities for the same area. At present there are 30 Sentinel-1 TOPS acquisitions and 20 ALOS-2 wide swath acquisitions, in our preferred, descending, viewing geometry. The irregular recurrence of ERS acquisitions from 1992-2000 leads to low coherence overall in the highly vegetated and rugged terrains of the area and high coherence within the sparse cities that span the fault. From our preliminary processing of 24-day interferograms, Sentinel-1 has the potential for higher coherence along the faults which can provide more observations of fault creep outside of the city limits.
[Authors] [ Overview programme] [ Keywords]
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Paper 214 - Session title: Poster Session 1
Tuesday-55 - InSAR Results From The WInSAR Consortium
Lu, Zhong (1); Meyer, Franz (2); Funning, Gareth (3); Johanson, Ingrid (4); Wauthier, Christelle (5); Pritchard, Matt (6); Baker, Scott (7); Fielding, Eric (8) 1: Southern Methodist Univ, United States of America; 2: Univ of Alaska Fairbanks, United States of America; 3: University of California Riverside, United States of America; 4: US Geological Survey, United States of America; 5: Pennsylvania State University, United States of America; 6: Cornell University, United States of America; 7: UNAVCO, Inc., United States of America; 8: Jet Propulsion Laboratory, United States of America
Show abstract
WInSAR is a consortium of non-commercial scientists at over 230 institutions engaged in radar remote sensing research and education, with major emphasis on interferometric synthetic aperture (InSAR) studies. WInSAR is hosted by UNAVCO, Inc. and both organizations are non-profit, membership-governed groups funded by the National Aeronautics and Space Administration (NASA), the National Science Foundation (NSF), and the U.S. Geological Survey. To help maximize the scientific return of radar data, WInSAR provides password-protected data access with partners including the Geohazard Supersite and Natural Laboratories initiative of the Group on Earth Observations (GEO), the Alaska Satellite Facility, and the various space agencies. Data access follows the regulations from the space agency that created the data, and so there are different amounts of data available to different approved investigators and depending on the country of origin of the WInSAR member. All members have access to the Caltech/JPL/Stanford open source software called ISCE (InSAR Scientific Computing Environment), and even non-members can attend the annual short courses hosted by UNAVCO. We present here a summary of recent results by WInSAR scientists that are based largely or in part on Sentinel, Envisat, and ERS-1/-2 SAR data analysis, with additional SAR data from other satellites and the NASA airborne UAVSAR InSAR system. Studies have addressed InSAR technique development and deformation related to the earthquake and volcano cycles, landslides, subsidence due to groundwater withdrawal and subsurface energy production (including hydrocarbons and geothermal), glaciers, and wetland dynamics in a number of locations. These studies include assessment, forecasting, and response to geohzards as well as fundamental research about Earth processes.
[Authors] [ Overview programme] [ Keywords]
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Paper 220 - Session title: Poster Session 1
Tuesday-98 - Analysis of coherence seasonal variation in Qinghai-Tibet Permafrost- A case study in Beiluhe area
Zhang, Zhengjia (1,2); Wang, Chao (1); Zhang, Hong (1); Tang, Yixian (1); Xu, Lu (1,2) 1: Institute of Remote Sensing and Digital Erath,CAS, China, People's Republic of; 2: University of Chinese Academy of Sciences,China, People's Republic of
Show abstract
The Qinghai-Tibet Plateau (QTP), the highest plateau in the world, affects its surrounding environments and climate directly through atmosphere and hydrological process. And the permafrost state and dynamics in QTP are sensitive indicators of the global change. Global warming has influence on the permafrost thaw and froze processes, then on its carbon storage. The status of permafrost in Tibet is the sensitive indicator of global climate change. Many works have been done on the permafrost in Tibet and its impact on the infrastructure construction, especially since 2006 when the Qinghai-Tibet Railway (QTR) was completed. Therefore, it is significant to study the permafrost environment in QTP.
Due to the advantages of the high resolution and large coverage, Synthetic Aperture Radar Interferometry (InSAR) has been used for permafrost deformation monitoring and soil moisture retrieving and good results have been obtained. However, in permafrost area due to the global change, seasonal temperature change, vegetation and soil moisture change, the backscattering feature of the ground targets would change greatly, which would contribute to decorrelations and limit the application of InSAR in permafrost region. Coherence is an important parameter, which is a good indicator of the phase stability of the scatterer. Seasonal coherence analysis of the permafrost area can be useful for many applications. Therefore, studying the seasonal coherence variation could be a useful for understanding permafrost environment and other applications.
In this paper, time-series coherence map have been generated. And coherence seasonal variation of typical ground targets in Beiluhe area has been analysed. Moreover, the relationship between the coherence variation and soil moisture have been conducted and analysed. In the coherence map generation step, adaptive window has been adopted, which would decrease the overestimation of coherence. In order to get the soil moisture, a time-series approach has been used and the results have been validated by the in situ measured soil moisture. For this study, time-series images with HH polarization have been used and 136 interferograms have been generated. Time-series coherence maps have been obtained and the coherence seasonal variation of typical ground targets have been analysed.
The test site is located in the southwest of Qinghai Province, China. The coverage of the SAR image is approximately 4×8 km2. The temperature changes greatly from summer to winter with the maximum high and low air temperatures reach approximately 23°C and -38°C. Due to such a greatly temperature change, permafrost environment is various and vulnerable. It is low-temperature permafrost region with continuous perennial permafrost and ice-rich active layers. Through amplitude map, google map, and the filed photos of the study site, it can be seen that typical ground targets in this study area could be classified into 5 classes: railway, highway, alpine steppe, barren, and alpine meadow. From the field photos of the typical ground targets in winter and summer season, it can be seen that except for railway and highway, surface environment in the other three types change greatly from winter to summer, especially in alpine meadow area. A mountain region is located in the northwest of the study areas. Four field campaigns were performed to collect the ground truth when TerraSAR-X flew over the test site. One was on Mar. 8-13, 2016 in the winter season. And the others were on Aug. 12, 2015 and Jul. 29, Aug. 9, 2016 in the summer season. During the field campaigns, temperature and soil moisture data were collected.
To monitor the seasonal coherence variable of the study area, 17 TerraSAR-X ascending images acquired from June 2014 to August 2016 with an observation angle of 23.5 degrees and ‘HH’ polarization were used. The pixel spacing of the complex image in range and azimuth direction was 0.454 m and 0.167 m, respectively. After all the radar images have been co-registrated with the master image, 136 interferograms have been generated. A 6×1 multi-look window was used in the interferogram generation process. Then using the SRTM co-registrated to the master image to monitor topographic phase, differential interferograms were obtained. And the Goldstein filter is applied to reduce the noise in the process step. After getting the time-series coherence maps, a time-series approach has been proposed and applied and the results have been validated by the in situ measured soil moisture. In the time-series approach, a linear retrieving model was proposed using the time-series SAR images under the assumption that the lowest backscattering coefficients were measured when the soil moisture is at its wilting point and the highest backscattering coefficients represent the water-saturated soil state. More information about the soil moisture retrieving using time-series method can be found in other references. The relationship between the coherence variation and soil moisture have been conducted and analysed.
Experimental results show that railway and highway hold high coherence during the whole observation, with the maximum value over 0.8. The mountain slope and barren area show medium coherence, which are about 0.4. The alpine meadow area shows lowest coherence value, which is less than 0.25. In the mountain slope, barren and alpine meadow areas, the coherence shows obvious seasonal variation. It can be explained that in the summer season, the soil moisture increase due to the permafrost thawing and rainy and ground typical targets change greatly, which results in the decorrelation. In winter season, most of the study areas are in dry and stable condition and the surface backscattering changes little, and most of the area shows high coherence. And the coherence value in alpine meadow shows obvious seasonal feature. High-resolution SAR coherence provides a new tool for permafrost environmental condition study. Future work will focus on the soil moisture retrieving and relationship between the coherence variation and soil moisture.
[Authors] [ Overview programme] [ Keywords]
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Paper 225 - Session title: Poster Session 1
Tuesday-58 - Time-series Analysis of Sentinel-1 TOPS Images Spanning Small Earthquakes
Luo, Heng (1); Wang, Teng (2); Liao, Mingsheng (1,3) 1: State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University, Wuhan 430079 China; 2: Earth Observatory of Singapore, Nanyang Technological University; 3: Collaborative Innovation Center for Geospatial Technology, Wuhan, 430079 China
Show abstract
Terrain Observation by Progressive Scans (TOPS) mode from the Sentinel-1A/B satellites provides us with up-to-date high-quality Synthetic Aperture Radar (SAR) images over a large coverage, which makes it widely applied to large/shallow earthquakes. However, the strategy of TOPS-based time-series analysis on small/deep earthquakes was rarely studied yet. Recently, a series of M<7 earthquakes occurred on the Qinghai-Tibet plateau, which usually have relatively smooth ground displacement disturbed by strong atmosphere influence. And the coherence of two pair of images span these earthquakes was not often desirable duo to the complex topography. Here we present a novel Sentinel-1 TOPS images analysis strategy with applications to 3-5 earthquakes occurred on the Qinghai-Tibet plateau since 2015. To study these earthquake, we collected time-series Sentinel-1 TOPS images acquired before and after earthquakes. The processing chain of TOPS time-series data was developed and was applied to estimate the coseismic displacement offsets from the time-series signals on detected persistent scatters. Our results show that the temporally uncorrelated atmospheric signal was largely eliminated and the subtle coseismic displacement signal can be extracted more precisely than single interferogram.
[Authors] [ Overview programme] [ Keywords]
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Paper 230 - Session title: Poster Session 1
Tuesday-107 - Land-fast Ice Event Based on Sentinel-1 Repeat Pass Interferometric Images in Gulf of Bothnia
Marbouti, Marjan (1); Praks, Jaan (2); Gegiuc, Alexandru (3); Antropov, Oleg (2,4); Lepparanta, Matti (1); Rinne, Eero (3) 1: Department of Physics, University of Helsinki, Helsinki, Finland;; 2: Department of Radio Science and Engineering, Aalto University, P.O. Box 13000, 00076 AALTO, Finland;; 3: Finnish Meteorological Institute, Marine Research, Erik Palménin aukio 1, 00560, Helsinki, Finland;; 4: VTT Technical Research Centre of Finland, P.O. Box 1000, 02044 VTT, Finland
Show abstract
This study presents first results on Sentinel-1 synthetic aperture radar interferometry in the Gulf of Bothnia winter scenes. Several repeat pass interferometric scenes over the ice areas were acquired and analyzed. The interferograms were built by using Sentinel-1A (IW mode) images with a temporal baseline of 12 days for winter months of 2015. Our results show, that the surface of landfast ice is stable enough to preserve coherence over the 12 day baseline. Previous InSAR studies on sea ice have used considerably shorter, 1 day temporal baselines. For the first time, we demonstrate Sentinel-1 SAR repeat pass interferometry applicability for sea ice deformation mapping. Signals in SAR interferometry may be due to atmospheric influence on the ice surface, ice-ocean interaction, or mechanical deformation of the ice cover.
According to our results, a high resolution map of landfast ice changes can be made based on Sentinel-measurements. In case of deformation, the information can be used in investigation of the rheological behavior of landfast ice, which is a major open topic in coastal ice engineering and in the boundary zone treatment in basin wide sea ice modeling. It is known that the breakage of land fast ice and the nature of the deformation that follows, are related to ice loads on structures, erosion of bottom and shore areas, and safety issues related to traffic and recreational activities on ice. The interferometric phase is sensitive to small discontinuous slips and continues deformation, which occur in coastal sea ice and which are difficult to map over two-dimensional areas by other methods.
Thus the Interferometric SAR can provide new insight into the mechanics of landfast ice. In the present conference several Sentinel-1A interferograms will be presented along with interpretation concerning the ice dynamics and physical properties. Moreover, the Sentinel-1 Interferometry will be compared with TanDEM-X interferometric scenes and generated DEM properties and potential of various temporal and spatial baseline configurations will be discussed.
[Authors] [ Overview programme] [ Keywords]
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Paper 231 - Session title: Poster Session 1
Tuesday-146 - X- and C-Band InSAR data to identify local effects following the 2016 Central Italy seismic sequence
Montuori, Antonio (1); Polcari, Marco (1); Albano, Matteo (1); Bignami, Christian (1); Moro, Marco (1); Saroli, Michele (2); Stramondo, Salvatore (1); Tolomei, Cristiano (1) 1: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Italy; 2: Università degli studi di Cassino e del Lazio meridionale
Show abstract
The 2016 Central Italy seismic sequence consisted of more than three months long sequence, and still on going, that produced several damages in the areas surrounding the epicenters of the earthquakes causing hundreds of victims. The surface displacement fields due to the main events occurred on August and on October respectively, were effectively constrained by means of X-, C- and L-band InSAR data. The retrieved results revealed significant deformation patterns close the Amatrice, Visso and Norcia towns showing ground subsidence values greater than 20 cm.
Moreover, we also observed some local complexities in the interferometric fringes patterns, not directly attributed to the main tectonic patterns. These local effects were effectively analyzed by Cosmo-SkyMed (X-band) and Sentinel-1 (C-band) data because of their wavelength more suitable to the scale of the investigated phenomena. In particular, we detected a clear local signal along the Mount Vettore, the highest mountainous relief of the Mount Sibillini, following the Mw 6.0 Amatrice/Accumuli earthquake. It was constrained by Cosmo-SkyMed data acquired along both the ascending and descending track.
In addition, a deformation pattern was observed by Sentinel-1 and Cosmo-SkyMed descending data along the already known Deep-seated Gravitational Slope Deformation (DGSD) of Mt. Frascare, in the proximity of the Fiastra Lake Dam.
Finally, the seismic events of October 2016 produced some interferometric fringes (with the number depending on the used frequency band) along the sector of Mount Sibillini at the eastside of Acquacanina district.
Geomorphological and geological post-processing analysis allowed us to ascribe such patterns to ground displacement occurred along local effects due to gravitative and karst phenomena.
[Authors] [ Overview programme] [ Keywords]
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Paper 233 - Session title: Poster Session 1
Tuesday-155 - Neural Network multisensor approach: an application to satellite data for earthquake damage assessment
Piscini, Alessandro (1); Romaniello, Vito (1); Bignami, Christian (1); Anniballe, Roberta (2); Stramondo, Salvatore (1) 1: Istituto Nazionale di Geofisica e Vulcanologia, Italy; 2: DIET, Sapienza University of Rome
Show abstract
Artificial Neural Networks (ANN) is a valuable and well-established inversion techniques for the estimation of geophysical parameters from satellite images. Indeed, once trained they are able to generate very fast products for several types of applications. One field of applications of ANN is the damage assessment after disastrous events. In particular, satellite remote sensing is an effective and safe way to detect and to map earthquake damage for contributing to post-disaster activities during the emergency.
This work aims at presenting an application dealing with Artificial Neural Networks for inverse modelling addressed to the evaluation of buildings collapse ratio (CR), defined as the number of collapsed building respect to the total of building in a city block, due to an earthquake, using both optical and SAR satellite data.
In this study a Neural Network was implemented in order to emulate a regression model and to estimate the CR as a continuous function. The adopted Neural Network was trained using some features obtained from Sentinel-2 optical and COSMO-SkyMed SAR images, as inputs, and the corresponding values of collapse ratio obtained from the survey of 2010 M7 Haiti Earthquake, i.e., our target output.
As regards to the Optical Data, we selected some change indexes. They are: the Normalized Difference Index (NDI), and two quantities coming from the Information Theory, namely the Kullback-Libler divergence (KLD) and Mutual Information (MI). Concerning the SAR images, the correlation Intensity Difference (ICD) and the KLD Parameter have been chosen.
The computation of such change indexes has been performed at object scale by considering a set of polygons, extracted from the open source Open Street Map (OSM) geo-database, corresponding to city blocks of the affected areas (the city of Port-au-Prince).
The demonstration of collapse ratio retrieval is then proposed for 1999 M7.6 Izmit (Turkey) and 2016 M6 Amatrice (Central Italy) earthquakes.
Despite of the results of validation, both for Izmit and Amatrice independent datasets, which provided Root Mean Square Errors (RMSE) between neural network outputs and targets with values lower than corresponding standard deviation, the neural network seems to underestimate damage for both test cases, mainly in the case of high damage values (CR higher than 0.5), probably because these high values were not well represented during training phase (only 3% of training samples). Furthermore, a sort of uncertainty is given by the Ground Truth itself, which is defined as the number of collapsed building respect to the total of building in a polygon, probably not a reliable representation of collapse ratio. This aspect results in creating a not very accurate dataset both for training and validation dataset.
Nevertheless, considering that the technique is independent by different typology of input data both for radiometric characteristics and spatial resolution the study demonstrated the feasibility to estimate damaged areas using the proposed approach, and its importance in near real time monitoring activities, owing to its fast application
[Authors] [ Overview programme] [ Keywords]
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Paper 234 - Session title: Poster Session 1
Tuesday-63 - Sar Intterferometry For Identification Of Environmental Phenomena – Case Of Albania
Frasheri, Neki; Beqiraj, Gudar; Bushati, Salvatore Academy of Sciences of Albania, Albania
Show abstract
During the project ESA 30467 we used SAR interferometry and phase image processing to investigate environmental changes in territory of Albania. Significant fringes are identified in part of hilly ranges of Preadriatic Depression as well as in other mountainous areas in northeastern part of the country. The phenomena is considered of environmental origin and is subject for future field studies. Interferograms showed no significant changes in the area of critical landslide of Ragami in the shores of hidropower plant lake of Vau Dejes. Results were consolidated comparing with precious studies (ESA project 14921). Further processing of phase images showed slight correlation with relief and tectonic features. Small number of SAR images was used and some results were obtained using standard image processing software, supporting the concept of “citizen science” and involvement of small teams and even individuals with insignificant resources for environmental studies based on SAR data.
[Authors] [ Overview programme] [ Keywords]
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Paper 235 - Session title: Poster Session 1
Tuesday-4 - Allan Variance Computed in Space Domain: Definition and Application to InSAR Data to Characterize Noise and Geophysical Signal
Cavalié, Olivier (1); Vernotte, François (2) 1: Nice University, France; 2: University of Franche-Comté, France
Show abstract
The Allan variance was introduced 50 years ago for
analyzing the stability of frequency standards. In addition to its
metrological interest, it may be also considered as an estimator of
the large trends of the power spectral density (PSD) of frequency
deviation. For instance, the Allan variance is able to discriminate
different types of noise characterized by different power laws in
the PSD. The Allan variance was also used in other fields than
time and frequency metrology: for more than 20 years, it has been
used in accelerometry, geophysics, geodesy, astrophysics, and even
finances. However, it seems that up to now, it has been exclusively
applied for time series analysis. We propose here to use the Allan
variance on spatial data, and in particular for InSAR. The main limitation of the technique is the atmospheric disturbances that affect the radar signal while
traveling from the sensor to the ground and back. In this paper,
we propose to use the Allan variance for InSAR measurements. The Allan variance was computed in XY mode as well as in radial mode for detecting different types of behavior for different space-scales, in the same way as
the different types of noise versus the integration time in the
classical time and frequency application. We found that radial
Allan variance is the more appropriate way to have an estimator
insensitive to the spatial axis and we applied it on SAR data
acquired over eastern Turkey for the period 2003–2011. Spatial
Allan variance allowed us to well characterize noise features,
classically found in InSAR such as phase decorrelation producing
white noise or atmospheric delays, behaving like a random walk
signal. We finally applied the spatial Allan variance to an InSAR
time series to detect when the geophysical signal, here the ground
motion, emerges from the noise.
[Authors] [ Overview programme] [ Keywords]
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Paper 237 - Session title: Poster Session 1
Tuesday-71 - Potential of Bistatic TanDEM-X in Crop land Extraction
Xu, Lu (1,2); Zhang, Hong (1); Wang, Chao (1); Zhang, Zhenjia (12) 1: Institute of Remote Sensing and Digital Erath,CAS, China, People's Republic of; 2: College of Resource and Environment, University of Chinese Academy of Sciences
Show abstract
The demand for agriculture monitoring and mapping is increasing since the food management is an essential problem for many countries. Synthetic aperture radar (SAR) images are of particular advantages due to the capability of all-day and all-weather imagery, which makes it a useful tool in crop mapping and classification. Studies have been carried out concerning crop land mapping with polarimetric SAR (PolSAR) images of C-band and L-band. Polarimetric decompositions which are utilized to separate different scattering mechanisms greatly assist in discriminating crops from other ground objects, and microwaves with longer wave lengths are more proper in vegetation detection for the better penetration ability as well. Generally, single-polarimetric (single-pol) X-band SAR images face limitations in the extraction of crops because of the shortage of discriminating features, which makes the utilization of multi-temporal analysis necessary. However, the inconsistent in polarimetric modes and acquisition conditions makes it difficult to achieve good results and nearly impossible for practical application in large area.
Nevertheless, the TanDEM-X mission designed by German Aerospace Agency (DLR) might be the solution. The aim of the TanDEM-X mission is to generate high-resolution digital elevation model (DEM) meeting the requirements of HRTI-3 accuracy with single-pass interferometric SAR images. The TerraSAR-X (TSX) and TanDEM-X (TDX) sensors form a helix formation and operate in bistatic mode to make the temporal baseline zero and thus eliminate temporal decorrelation. The application of TanDEM-X interferometric SAR data has been illustrated in forest height estimation, forest/non-forest mapping, paddy rice monitoring and crop type discrimination. In this paper, we examine the practicability in another aspect: crop land extraction from suburb area.
The study area is located in Dongguan city, Guangdong Province, China. The VV polarimetric bistatic TSX/TDX data was acquired on December 19th 2015, covering 22.73°N to 23.24°N, 113.53°E to 113.94°E. The TSX is the active sensor which transmits and receives signals, and the TDX is the passive sensor which only receives the reflected signal from ground objects. The urbanization of Dongguan city is of very high level, which means an intensive construction distribution and small agricultural parcels. The detailed classification map in this area with single-pol and single-frequency data is difficult. On one hand, the high proportion of double-scattering from dihedral and trihedral structures of buildings strongly disturbs the discrimination of vegetation; on the other hand, different crops located closely to each other due to the small cultivated acreage, such as banana, papaw, mango, eucalyptus and kinds of vegetables, according to field survey. These all hinder the precise classification of different vegetation types. So in this paper we only intend to separate all crop lands apart from other objects. The fact that even though some cultivation parcels are sparsely spread, most agricultural areas are distributed in periphery suburb of central city enables the extraction of crop land.
The process of crop land extraction contains three steps. The first step is preprocessing stage which includes multi-look and necessary filtering. In this experiment we adopt 5 × 4 looks in azimuth × range direction. And Enhanced Lee filter is applied to the TSX and TDX amplitudes in a 3×3 window. Secondly, the feature extraction stage which extracts information from bistatic TSX/TDX data should be carried out. The SRTM DEM data is utilized to mask the mountain area in order to reduce the shadow of Dalingshan Mountain for the forest is not our goal. The coherence is calculated in this stage, along with the coefficient of variation (COV) and texture information. The coherences of crop lands are higher than urban buildings and water bodies because of the zero temporal baseline between TSX and TDX data. The COV is estimated in a 5×5 window, which reflects the dispersity of active sensor image amplitude. Since the urban area contain diversiform of buildings and artificial structures, the back-scattering intensity could vary greatly even in a small area. On contrast, the crop lands though might contain multiple crop parcels, share a low COV for the rather homogeneous growth status in the same parcel. The mean coherences of sampling crop lands and urban buildings are 0.90 and 0.73; and the mean COVs are 0.25 and 0.59. The analysis of histogram shows separability of crop lands and urban building. Finally, the SVM classifier is used to train the feature set with sampling areas. The crop mapping results corresponds to the optical image acquired by google earth and is in accordance with the field survey result.
In conclusion, this paper investigated the utility of bistatic TanDEM-X with single-pol image for suburb area crop extraction. Since the suburb area is usually complex in both polarimetric and texture signatures, we assume that the utilization of interferometry might bring helpful information, which is validated by the effectiveness of coherence. Future works would concentrate on more accurate crop mapping around suburb area and even in urban region with multi-temporal and multi-polarimetric images to further fulfill the demand of urban planning and crop monitoring.
[Authors] [ Overview programme] [ Keywords]
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Paper 243 - Session title: Poster Session 1
Tuesday-106 - Inter-annual modulation of seasonal glacial velocity changes in the Eastern Karakorum detected by ALOS-1/2 data
Usman, Muhammad; Furuya, Masato Hokkaido University, Japan
Show abstract
Whereas the ice sheets all over the world are receding, the glaciers in Karakoram are either stagnant or advancing, which is known as ‘Karakoram anomaly’. The surging dynamics and mass balance have been extensively studied in this area. However, in the Eastern Karakorum Range, the spatial and temporal changes in glacial velocity have been so far poorly understood. We have analyzed nearly all the available ALOS-1/2 data in this area and have examined the inter-annual modulation of five glaciers. The glaciers with size >30km, i.e. Siachen, Baltoro and Eastern tributary of Kundos, are mostly showing a considerable velocity change in their various parts, accompanying clear seasonal changes both in ALOS-1/2 data. However, this change mostly depends upon the individual glacier and is variable in space and time. On the other hand, the smaller glaciers (<30km), i.e. Singkhu, Gasherbrum and Western tributary of Kundos glaciers, are showing a slowdown in ALOS-2 data. Analysis of the local air surface temperature data at five observatories indicates that during the same season, the temperature trend in the study area is uneven and probably varies significantly between different glaciers. It can result in localized warming/cooling that can affect the availability of melt-water for an individual glacier. The excess surface melt-water at each individual glacier may undergo a variety of en/sub-glacial hydraulic and hydrological processes that are further different at each glacier. Thus, it will result in a complex velocity behavior in this region.
[Authors] [ Overview programme] [ Keywords]
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Paper 245 - Session title: Poster Session 1
Tuesday-27 - Kinematic Analysis of Interseimic Motion on the Eastern Tibet Border Using LOS Velocity Maps Derived from Envisat and Sentinel-1 SAR Data
Doin, Marie-Pierre (1); Lasserre, Cécile (1); Pengchao, He (1); Nockles, Victoria (1); Replumaz, Anne (1); Shen, Zhenkang (2); De Sigoyer, Julia (1) 1: CNRS-ISTerre, France; 2: UCLA, USA
Show abstract
We use here SAR interferometry using Envisat and Sentinel-1 data to map the interseismic deformation of eastern Tibet. The area under study starts South of the Haiyuan fault, crosses the eastern termination of the Kunlun fault and the XianShuiHe fault to the South. It includes the Longriba fault system, an active structure located 150 km west of the Longmen Shan front (Xu et al., 2008, Ren et al., 2013). GPS data suggest that it delimits to the east the eastern movement of the Aba block. It may accommodate a large part of the present-day relative movement (6-8 mm/yr) between the Aba block and the south China block (Thatcher, 2007, Shen et al 2005). The Longriba and the Longmen Shan faults might be linked at depth by a decollement zone or by ductile shear in the crust (Shu et al., 2008). The interaction and deformation partitioning between the Longriba fault and the Longmen Shan faults may help explain the paradox observed across the Longmen Shan, i.e., the contrast between the large relief (4 km) and seismic activity (May 2008 Sichuan earthquake) and small interseismic convergence rate.
We process four Envisat and one Sentinel-1 1000~km long swaths crossing mountainous and vegetated terrains. The interferograms show numerous phase perturbations that mask the interseismic motion due to : (1) coherence loss (snow, vegetation, topography), (2) stratified atmospheric delays, (3) DEM error contribution, (4) for the Envisat data, the 2008 Sichuan earthquake and its post-seismic signal. We will show how we tackle these limitations and display the effect of all successive corrections.
Focus will be brought to three specific processing steps: (1) the strategy used here to coregister a pile of Sentinel-1 data using spectral diversity; (2) the stratified atmospheric correction applied before filtering and unwrapping, that increase phase spatial continuity. We use an empirical estimation based on local wrapped phase to elevation ratios to validate and refine global atospheric model predictions. (3) Unwrapping is obtained by a region growing algorithm, from the most reliable areas to the least.
Envisat time series of phase delay maps in the Longriba area are dominated by a side lobe of the May 2008 Sichuan earthquake. After its extraction and correction, principal component analysis clearly evidences a linear trend modulated south of the Longriba fault system by post-seismic transient motion, in agreement with GPS data (Huang et al., 2014). This post-seismic transient motion is estimated and removed from the time series. Finally, we obtain a velocity map of interseismic motion with an amplitude of a few mm/yr in Line Of Sight (LOS)t.
We first performed a first order comparison between horizontal GPS velocities projected into the LOS with various published GPS fields. Note that the velocity fields before and after the 2008 earthquake are found different by Rui and Stamps (2016). Our velocity field is in better agreement with that of Shen et al. (2009) using only pre-seismic data, and supports the existence of strain accumulation along the Longriba fault. This suggests that strain accumulation may be partially released by slow creep on a decollement during the post-seismic period. The velocity field also displays a localized strain accumulation across the various segments of the XianShuiHe fault, and distributed strain across the termination of the Kunlun fault. The interseismic map is used to refine the block motions and traces of the main eastern Tibet faults and to discuss possible vertical motion.
[Authors] [ Overview programme] [ Keywords]
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Paper 253 - Session title: Poster Session 1
Tuesday-147 - Coseismic fault model of Mw 8.3 2015 Illapel earthquake (Chile) retrieved from multi-orbit Sentinel1-A DInSAR measurements
Solaro, Giuseppe; De Novellis, Vincenzo; Castaldo, Raffaele; De Luca, Claudio; Lanari, Riccardo; Manunta, Michele; Casu, Francesco IREA-CNR, Italy
Show abstract
On 16 September, at 22.54 UTC, an earthquake of Mw 8.3, at depth of 25 km, occurred off the coast of Central Chile in Coquimbo area, and the epicenter was located 46 km west of Illapel city. This earthquake occurs within the rupture zone of the 1943 M 8.1 seismic event. Since then, after many years of quiescence, the seismic activity of this plate interface suddenly increased in 1997; indeed, 7 events with M>6 occurred between July 1997 and January 1998 along this shallow dipping subduction zone.
In this work, a detailed coseismic slip fault model is presented, obtained by taking advantage of the wide spatial coverage and reduced revisit time offered by multi-orbit S1A data, as well as of the high accuracy measurements capability of DInSAR technique. In particular, we proceed following three steps.
Firstly, we generate two S1A interferograms for both ascending and descending orbits, respectively, and encompassing the main shock, in order to combine the displacements along the satellite Line Of Sight (LOS) for retrieving the EW and vertical components of deformation. The used dataset consists of four SAR acquisitions that were taken on the 26/08/2015 and 19/09/2015 along ascending orbits (Track 18), and 31/07/2015 and 17/09/2015 over descending ones (Track 156) by the C-Band S1A sensor acquiring data with the Terrain Observation with Progressive Scans (TOPS) mode, which is specifically designed for interferometric application and guarantees a very large spatial coverage.
S1A satellite measurements are a powerful tool to analyze the deformation induced by large mega-thrusting earthquakes, as in the case of the Illapel earthquake. More specifically, S1A peculiarities include wide ground coverage (250 km of swath), C-band operational frequency and short revisit time (that will reduce from 12 to 6 days when the twin system Sentinel-1B will be placed in orbit during 2016). Such characteristics, together with the global coverage acquisition policy, make the Sentinel-1 constellation to be extremely suitable for studying region of high seismic hazard and monitoring worldwide, thus allowing the generation of both ground displacement information with increasing rapidity and new geological understanding. The east-west displacement map highlights a huge westward displacement of about 210 cm, while the vertical displacement map shows an uplifting area of about 25 cm along the coast, surrounded by an annular shaped subsidence of about 20 cm.
Secondly, in order to retrieve the seismogenic fault parameters, we jointly invert S1A DInSAR ascending and descending data following two main steps: a non linear inversion to constrain the fault geometries with uniform slip, followed by a linear inversion to retrieve the slip distribution on the fault plane. The observed data is modeled with a finite dislocation fault in an elastic and homogeneous half-space. The Okada modeling consists of a reverse fault, accounting for the main seismic event and corresponding to the shallow portion of the subducted slab. Most of the slip occurred north-west of the epicenter at a distance of about 60 km. A large slip area of about 70 km along strike and 50 km along dip is found with a maximum slip located at a depth ranging from 10 to 30 km.
In addition, we extend our analysis by performing a 2D numerical modeling of the ground deformation pattern retrieved by the DInSAR measurements; our solution is based on the FE approach and allows us to account for the geological and structural information available over the considered area, as well as the seismicity distribution. The FE modeling, obtained by including in our analysis also geological and structural information, allows to estimate values of maximum slip comparable with the analytical solution and to evaluate the von Mises distribution and axis stress orientation which are in agreement both with the location and type of faulting of the aftershocks.
Finally, we propose a conceptual model with the aim of synthesizing the kinematics of the megathrust faulting inferred from our modeling results and supported by observed data. Such a model shows how the megathrust subduction induces a horizontal displacement toward West, an uplift along the coast and a subsidence behind it of the overriding plate; in the same way, the motion along the subducted slab, considering the distribution of von Mises stress, could explain the occurrence of normal faulting earthquakes (extensional regime) across the trench axis and thrust faulting (compressive regime) along a deeper segment of the slab.
[Authors] [ Overview programme] [ Keywords]
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Paper 256 - Session title: Poster Session 1
Tuesday-49 - Mapping crustal deformation in the Red River Fault zone using InSAR
Chen, Jiajun; Li, Zhenhong; Clarke, Peter COMET, School of Civil Engineering and Geosciences, Newcastle University, United Kingdom
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In the past two decades, Interferometric Synthetic Aperture Radar (InSAR) has become a valued geodetic tool for mapping crustal deformation at the scale of hundreds of kilometres with a high spatial resolution (e.g. a few metres to tens of metres).
The Red River Fault (RRF) runs over 1000 km from southeast Tibet to South China Sea, and is a major strike-slip fault as a result of the collision of the India and Eurasian plates. The ground movements in the RRF zone have not been well investigated for two reasons: (i) the large topography variations make it difficult to collect ground observations including GNSS, and (ii) the heavy vegetation together with variable climate makes InSAR observations a challenge.
Sentinel-1A was launched in April 2014, Sentinel-1B in April 2016 and both have been collecting data routinely. In the RRF zone, Sentinel-1 data are being acquired every 12/24 days with both satellites. The small temporal baseline, together with small spatial baselines (i.e. orbital separations) greatly improve interferometric coherence at C-band. In addition, Sentinel-1 images cover a wide footprint, 250 km from near to far range in Interferometric Wide Swath (TOPS) mode. Since October 2014, there have been over 400 Sentinel-1 images collected from 4 descending and 3 ascending tracks covering the RRF zone. Also, over 1500 ALOS-1 images collected between 2007 and 2011 are available in this region, and ALOS-2 data are being systematically acquired since 2014. The long wavelength (L-band) of ALOS-1/2 ensures good coherence. All the above-mentioned factors make it now possible to use InSAR to monitor slow-slip crustal deformation in this region.
The SAR data are interferometrically processed using our automatic processing chain based on the InSAR Scientific Computing Environment (ISCE) software, and the interferograms are calibrated for atmospheric water vapour using high-resolution ECMWF products. Finally, time series analysis is performed to determine the interseismic deformation rate of the RRF using the in-house InSAR time series with atmospheric estimation model (TS + AEM) package. The implications of our InSAR measurements for future seismic hazard in the RRF zone are discussed.
[Authors] [ Overview programme] [ Keywords]
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Paper 259 - Session title: Poster Session 1
Tuesday-104 - Ice velocity monitoring over northern Greenland glaciers measured with Sentinel-1a/b data
Lemos, Adriano; Shepherd, Andrew; McMillan, Malcolm; Hogg, Anna; Hatton, Emma CPOM - University of Leeds, United Kingdom
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Most of the Greenland mass loss, especially in the northern region, is through ice discharge. Systematically monitoring Greenland’s outlet glaciers is essential to understand the timescales over which glaciers evolve and enable better projection of future contribution of ice sheets to sea level rise to be made. The new Synthetic Aperture Radar constellation, composed by Sentinel-1a launched in 2014 and, most recently, Sentinel-1b in 2016 released by the European Space Agency, offers the opportunity for continued monitoring of the evolution of glaciers flow. This work provides surface ice velocities estimated through an intensity tracking algorithm, using Sentinel-1a/b (Interferometric Wide Swath) images over key northern marine terminating glaciers in Greenland, Petermann Glacier and 79°N Glacier. We generated high temporal resolution glacier's surface velocities using 12 to 6 days repeat period images from October/2014 to the present. The two years of continuous dataset allowed us to explore the spatial as well as the seasonal variation over these glaciers.
[Authors] [ Overview programme] [ Keywords]
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Paper 265 - Session title: Poster Session 1
Tuesday-46 - 2D Finite Element modelling of the 2015 Gorkha earthquake through the joint exploitation of DInSAR measurements and geologic information
Tizzani, Pietro; De Novellis, Vincenzo; Castaldo, Raffaele; Solaro, Giuseppe; Pepe, Susi; De Luca, Claudio; Bonano, Manuela; Manunta, Michele; Casu, Francesco; Zinno, Ivana; Lanari, Riccardo IREA-CNR, Italy
Show abstract
The Gorkha earthquake (Mw 7.8) struck Nepal on 25 April 2015 at 06:11:26 UTC, killing more than 9,000 people and producing extensive damages. The main seismic event had its epicenter localized at ~82 km NW of the Kathmandu city and the hypocenter at a depth of approximately 15 km. About 100 aftershocks occurred during the following months, propagating toward the southeast direction. The rupture mechanism is in agreement with the convergence of the Indian plate toward Eurasia at an overall rate of about 45 mm/yr, with about 20 mm/yr driving the uplift of the Himalayan Arc. The kinematics and size of the earthquake are consistent with the décollement associated with the Main Himalayan Thrust (MHT).
We exploit two DInSAR interferograms retrieved from an S1A and an ALOS-2 SAR data pair. We generate the former by using two SAR images that were acquired on the 17th and 29th April 2015 over descending orbits by the C-Band (5.6 cm wavelength) S1A sensor. Concerning the latter interferogram, it is relevant two L-band ALOS-2 (23 cm wavelength) SAR data acquired over descending orbits on the 22th February and 3rd May 2015, respectively. We also benefit from four GPS stations, falling within the area of the retrieved deformation, deployed by the Caltech Tectonics Observatory. The DInSAR measurements profiles are compared with the LOS-projected GPS measurements (see the values reported in the table below), and refer only to the common areas; both evaluated with respect to the SNDL station and to a coherent pixel of the DInSAR interferograms close to this station, respectively. We compare the S1A and the ALOS-2 best-fit solutions with the corresponding LOS-projected results of the FE model along the considered section, respectively.
We reproduce the retrieved displacements by constraining the sub-domain setting with the geological and structural information by analyzing the measured deformation pattern within a 2D structural mechanical context, under the plane strain approximation. We use information on: the geometric features of the active seismogenic structures, the effects of the mechanical heterogeneities, the physical constraints on the ground deformation pattern. As boundary conditions we apply a free constraint at the upper boundary domain, corresponding to the topography of the considered area. The bottom boundary is fixed, whereas a roller condition at the two sides of the numerical domain is applied. We assume different internal boundary settings, in order to simulate the tectonic contacts among the rock successions. In particular, we consider that: free mechanical constraints represent the media continuity; identity pairs, used to simulate the reactivation of a pre-existing fault, represent boundary along which the loading is concentrated and transferred to the sub-domain.
The modelled total displacement reveals maximum values along the MHT segment of about 7 m, which gradually decrease away from it; the displacement vectors on the surface show subsidence to the north and uplifting to the south. Our geodetic inversion suggests that the maximum slip is confined at a depth of 7–15 km along the MHT and occurred in the area about 30 km northern of Kathmandu; a slip amount of about 3 m is retrieved in correspondence to the midcrustal ramp dipping north of about 20°. A small displacement in the southern region along the MFT and the MBT splay faults (about 5 and 25 cm, respectively) is detected.
The novel aspect of our results is the finding of more than 3 m of deformation in correspondence to the shallow portion of the MCT, in the northern part of the investigated area. This is supported by other studies on the slip and deformation across this Himalaya region, which highlights the activity of the MCT, indicating the occurrence of significant deformation in correspondence to this thrust. Several authors emphasize that the MCT is not dormant, but it has been active in segments by clustering moderate size earthquakes. We further remark the existence of field evidences (surface fractures, landslides, building collapses) in correspondence to the MCT zone where we have identified high slip; this area is known in the literature as a physiographic transitional zone recently referred to as Pokhara-Gorkha Anticline.
Finally, to further assess our model, we analyze the stress distribution along the MHT rupture segment in terms of von Mises scalar quantity and orientation of the maximum principal stress, comparing this information with seismological data: the stress values on the tectonic structures are also shown (colored dots). In particular, the maximum principal stress orientation highlights a compressive regime in correspondence to the deeper portion of the MHT and an extensional regime at the shallower segment: this finding is supported by a first analysis, carried out on the available seismological data, which shows that at least one main aftershock (with Mw > 5.0) exhibits a high-angle normal faulting and various aftershocks share low-angle thrust faulting mechanisms consistent with the main shock geometry.
[Authors] [ Overview programme] [ Keywords]
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Paper 266 - Session title: Poster Session 1
Tuesday-131 - Global Approach To Solve The L1-Norm Phase Unwrapping Problem In Differential Radar Interferometry (D-InSAR) Analysis
Esch, Christina (1); Köhler, Joël (1); Gutjahr, Karlheinz (2); Schuh, Wolf-Dieter (1) 1: Institute of Geodesy and Geoinformation, University of Bonn, Germany; 2: Joanneum Research, DIGITAL Institute for Information and Communication Technologies, Graz, Austria
Show abstract
The Earth surface is subject to continuously occurring geophysical phenomena from geological as well as anthropogenic origin. Within the Lower-Rhine-Embayment in the southwest of North Rhine-Westphalia, Germany, the deformation is in the range of a few centimeter per year, for example. To detect these deformations as well as their temporal behavior differential radar interferometry (D-InSAR) data from several years are used. These data are stacked together and analysed with the Small BAseline Subset (SBAS) method.
As with all interferometric applications the problem of phase ambiguities occurs, hence the phase can only be measured modulo 2π. The process of adding the correct multiple of 2π is called Phase Unwrapping and plays a key role in deriving the valuable height information from SAR interferometric data.
A rather popular technique to reconstruct the phase is the Minimum Cost Flow (MCF) approach. The problem is recast into a network with nodes and arcs searching for the minimum cost flow, defined by the phase ambiguity factors. This can be carried out by choosing the weighted L1-norm for the error criterion. The basic algorithm only works within one single interferogram. In order to simultaneously unwrap multitemporal D-InSAR data, an extended version exists. This approach exploits both the spatial as well as the temporal information. However, it only works in a step-wise way. So first, Phase Unwrapping is performed in the temporal plane arc by arc and afterwards, these results are used in a second step to spatially unwrap the phase in each single interferogram. This step-wise extended basic MCF approach can be solved very efficient with help of network flow algorithms, as the RELAXIV algorithm, for example.
The aim of our project is to realize a consistent solution in an one-step algorithm. Therefore, the spatial as well as the temporal information are considered together in one global approach. In this contribution first methodological considerations are shown and applied to simulated data as well as to small test regions of stacked ERS 1/2 data.
[Authors] [ Overview programme] [ Keywords]
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Paper 270 - Session title: Poster Session 1
Tuesday-28 - Icecap velocity change affected by crustal deformation during the 2014-2015 Bardarbunga rifting event
Himematsu, Yuji; Furuya, Masato Hokkaido University, Japan
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The 2014-2015 Bardarbunga rifting episode is one of the largest event in Iceland. Previous studies have already reported earthquake swarm with epicentral migration and fissure eruption at northern part of Vatnajokull icecap, which is the largest icecap in Iceland. The crustal deformation due to the episode have also been detected by using SAR interferograms. Although some papers indicated the interaction between the caldera collapse and sill closure of Bardarbunga, the relationship between the crustal deformation and the flow speed on Vatnajokull has neber been discussed.
In this study, we processed Sentinel-1A, ALOS-1/2 and Cosmo-SkyMed images to derive signals of icecap flow and crustal deformation associated with the rifting event. First, we focused on velocity change of icecap around Bardarbunga caldera. Comparing with the velocity during the pre-, co- and post-rifting episode, we could not identify the velocity changes associated with the event. Second, we focused on the surface deformation around Holuhraun, where the fissure eruption occurred. The offset tracking results from Cosmo-SkyMed images showed a graben structure with over 6 m of subsidence at the graben floor on the icecap due to the dike intrusion. Using these observation results, we will discuss the interaction between the ice and the crustal deformation during the 2014-2015 Bardarbunga rifting event.
[Authors] [ Overview programme] [ Keywords]
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Paper 274 - Session title: Poster Session 1
Tuesday-111 - Observation Of Glacier Changes In The Tropical Andes By SAR Remote Sensing
Seehaus, Thorsten; Braun, Matthias; Lippl, Stefan Friedrich Alexander Universität Erlangen-Nürnberg, Germany
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The glaciers of the tropical Andes are an important water resource, but they are highly affected by climate change. The regional water supply strongly depends on the melt water and consequently on the mass balance of the glaciers. Therefore, it is important to quantify the glacier changes in this region. Remote sensing, particularly SAR remote sensing, is an ideal tool to monitor such wide regions and to obtain information of the ongoing glaciological processes.
In this study data from different SAR sensors are analyzed in combination with other remote sensing data sets. Various glaciological variables (e.g., glacier extend, surface type, equilibrium line altitude, surface velocity) and their changes are determined. Bi-static SAR data from the TanDEM-X mission (2011-2014) are interferometrically processed in order to obtain short-term and in combination with SRTM data (2000-2014) longterm elevation change information. Geodetic glacier mass balances are derived from the obtained surface elevation change information. The potential of Sentinel-1A/B to determine elevation change data on glacier regions is tested in regions where coherence is retained between repeat pass acquisitions.
By analyzing the computed coherence pattern of repeat pass acquisition of different SAR sensors, especially Sentinel-1A/B, glacier outlines are determined. The results from this novel method are compared to observations using other methods like the Normalized Differenced Snow Index (NDSI) to obtain glacier extent.
The uncertainties in the resulting products are systematically analyzed by cross validation (e.g. with field data) and considering various influencing variables.
[Authors] [ Overview programme] [ Keywords]
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Paper 277 - Session title: Poster Session 1
Tuesday-29 - Estimation of displacement rates with radar interferometry near the Agua Blanca fault, Baja California
Riedel, Anika; Niemeier, Wolfgang; Riedel, Björn TU Braunschweig, Germany
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This investigation is embedded in the ECOAQUA Project and is carried out by the UNAM (Universidad Nacional Autónoma de México, Instituto de Ingeniería, City of Mexico), UABC (Universidad Autónoma de Baja California, Ensenada) and TU BS (Technische Universität Braunschweig). The main objective of the project is the evaluation of bio-economic risks due to overexploitation of Aquifer Systems in Baja California, Mexico.
The study area is located in an arid costal region in the northern part of the Peninsula of Baja California, 110 km south from the US-México border line. Geologically the region is characterized by coastal and alluvial flatlands, where the city of Ensenada and the croplands of Maneadero are found. These flatlands are surrounded by the Guadalupe and Ojos Negros intermountain valleys. The Agua Blanca fault is the southern border of our study area and extends from NW to SE as a 120 km dextral strike-slip fault. We try to estimate the displacement rates along the Agua Blanca fault with advanced InSAR techniques and compare our results with GPS measurements from the 1990s. Additionally, we try to separate the tectonic signal from possible anthropogenic signals, like landslides or subsidences through extensive water pumping from agricultural usage.
The InSAR technique has become a very valuable tool for the monitoring of earth surface changes by providing both mm-precision for surface change detection, monitoring tasks over time spans of days to years and m-precision for high resolution topographic mapping tasks. To overcome the limitations of temporal decorrelation, atmospheric effects and vegetation changes, advanced interferogram processing methods like Persistent Scatterer InSAR (PSI) and Small Baseline Subset Analysis (SBAS) were developed. The SBAS method will allow us to take into account the seasonal deformation in agricultural areas and relate it to changes in the thickness of the confined aquifer due to recharge and withdrawal of groundwater, whereas we use PSI methods in areas where we expect a higher sensitivity to small displacements in areas with high backscattering signal.
In this presentation we will show the preliminary results of surface changes in the vicinity and along the Agua Blanca fault derived from ENVISAT data from 2003-2010 in ascending and descending orbits based on a combination of SBAS- and PS- Interferometry processing. A comparison with 2 years of SENTINEL-1 data is still under processing.
[Authors] [ Overview programme] [ Keywords]
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Paper 279 - Session title: Poster Session 1
Tuesday-30 - Software Toolbox Development for Rapid Earthquake Source Optimisation Combining InSAR Data and Seismic Waveforms
Isken, Marius P. (1); Sudhaus, Henriette (1); Heimann, Sebastian (2); Steinberg, Andreas (2); Vasyura-Bathke, Hannes M. (3) 1: Kiel University, Institute of Geosciences Kiel, Germany; 2: GFZ, German Research Center for Geosciences, Potsdam, Germany; 3: King Abdullah University of Science and Technology, Saudi-Arabia
Show abstract
We present a modular open-source software framework (pyrocko, kite, grond; http://pyrocko.org) for rapid InSAR data post-processing and modelling of tectonic and volcanic displacement fields derived from satellite data. Our aim is to ease and streamline the joint optimisation of earthquake observations from InSAR and GPS data together with seismological waveforms for an improved estimation of the ruptures’ parameters. Through this approach we can provide finite models of earthquake ruptures and therefore contribute to a timely and better understanding of earthquake kinematics.
The new kite module enables a fast processing of unwrapped InSAR scenes for source modelling: the spatial sub-sampling and data error/noise estimation for the interferogram is evaluated automatically and interactively. The rupture’s near-field surface displacement data are then combined with seismic far-field waveforms and jointly modelled using the pyrocko.gf framwork, which allows for fast forward modelling based on pre-calculated elastodynamic and elastostatic Green’s functions. Lastly the grond module supplies a bootstrap-based probabilistic (Monte Carlo) joint optimisation to estimate the parameters and uncertainties of a finite-source earthquake rupture model.
We describe the developed and applied methods as an effort to establish a semi-automatic processing and modelling chain. The framework is applied to Sentinel-1 data from the 2016 Central Italy earthquake sequence, where we present the earthquake mechanism and rupture model from which we derive regions of increased coulomb stress.
The open source software frameworkis developed at GFZ Potsdam and at the University of Kiel, Germany, it is written in Python and C programming languages. The toolbox architecture is modular and independent, and can be utilized flexibly for a variety of geophysical problems.
This work is conducted within the BridGeS project (http://www.bridges.uni-kiel.de) funded by the German Research Foundation DFG through an Emmy-Noether grant.
[Authors] [ Overview programme] [ Keywords]
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Paper 284 - Session title: Poster Session 1
Tuesday-84 - Ability of Sentinel-1 for monitoring structure displacements - case study of Ostrava bridges
Hlavacova, Ivana (1); Kolomaznik, Jan (1); Lazecky, Milan (2,1) 1: GISAT, s.r.o., Czech Republic; 2: IT4Innovations, VSB-TU Ostrava, Czech Republic
Show abstract
The Sentinel-1 satellite constellation was designed to monitor large-scale events, such as floods, landslides, volcanoes or subsidences. The infrastructure, such as bridges, dams or pipelines, was left for the high-resolution satellites (TerraSAR-X, Cosmo-SkyMed), which proved to be very useful for monitoring of these objects.
On the other hand, the availability of large amounts of Sentinel-1 data give us the possibility to see the infrastructure from 3 or even 4 different viewing directions, allowing us to see the object from different sides and to estimate the vertical and east-west component of the movement.
We present the results of monitoring several bridges in Ostrava, Czech republic, built in an area which has been undermined years ago, and is still slowly subsiding. Bridges are monitored due to the movements on their edges, and close to them, there are other objects, such as acoustic walls, which show out a significant uplift in some tracks (2-3 cm/year), probably due to their tilt.
Sometimes, it is impossible - in comparison to high-resolution data - to recognize close objects from which the radar ray reflects, but the possibility to compare the different viewing angles allows us to partially validate the results.
The estimated movement velocity accuracy of Sentinel-1 dataset of appr. 40 images is comparable to a TerraSAR-X dataset of 23 images, however the height accuracy is much worse for the Sentinel-1 (due to short perp. baselines), making it sometimes difficult to recognize the points on the bridge from the points under it.
[Authors] [ Overview programme] [ Keywords]
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Paper 285 - Session title: Poster Session 1
Tuesday-31 - Slip Rates Along the Sagaing Fault, Myanmar, From Sentinel-1 InSAR Time-Series Analysis
Piromthong, Pawan; Hooper, Andrew; Elliott, John University of Leeds, United Kingdom
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The Sagaing Fault is a major fault in Southeast Asia which acts as a transform fault between the Burma microplate and the Sunda plate. The fault runs predominantly north-south through Myanmar, close to many major nearby cities with populations in the millions, thus posing a substantial risk from future earthquakes. GPS studies indicate that the Sagaing Fault is accumulating significant strain. They also suggest variable slip rates along the fault, although the density of GPS network is not sufficient to understand the potential variability along the whole fault. Problems of incoherence have made it difficult to study this region using InSAR previously, but Sentinel-1, with its reduced revisit time is able to track displacements through time. We present InSAR time-series analysis results from 2 tracks of Sentinel-1 from 2015 to 2016, which cover the length of the fault. We use the results to estimate the present-day interseismic slip rates and locking depth along the fault and discuss the implications for regional tectonics and seismic hazard.
[Authors] [ Overview programme] [ Keywords]
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Paper 287 - Session title: Poster Session 1
Tuesday-32 - Interseismic Deformation along the Altyn Tagh Fault from Sentinel-1 InSAR
Shen, Lin; Hooper, Andrew; Wright, Tim J.; Elliott, John COMET, School of Earth and Environment, University of Leeds, United Kingdom
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The 2000 km-long Altyn Tagh Fault (ATF) is a major intra-continental, left-lateral strike-slip fault, which trends approximately E-W at the northern border of Tibetan plateau. Estimates of slip rate along the ATF suggest that there is a possible discrepancy, for some sections at least, between the relatively lower geodetic measurements and the 2-3 times greater geological measurements. This discrepancy may be due to the uncertainties of measurements, or may indicate a secular change in fault slip rates over distinct time scales. Therefore, accurate slip rate determination along the ATF is needed to understand the tectonic processes active in this region. As a space geodetic tool, Interferometric Synthetic Aperture Radar (InSAR) is well suited to estimate current interseismic slip rates of the ATF. In particular, Sentinel-1 offers the best potential to generate precise surface displacements along the whole ATF, which was difficult to achieve with previous SAR sensors. We present here preliminary results of displacements and slip rates estimated from two years of Sentinel-1 data for the whole western ATF, thus offering a detailed picture of the spatial distribution of interseismic strain rate over a wide region. We discuss the implications of our results on the competing models of Indo-Asian convergence, which support contrasting views of how continents deform in Tibet, and on seismic hazard for the region.
[Authors] [ Overview programme] [ Keywords]
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Paper 291 - Session title: Poster Session 1
Tuesday-148 - Surface Deformation Field And Source Modelling Of The Seismic Sequence Of August-October In Central Italy
Bignami, Christian; Geodetic Group, Ingv Istituto Nazionale di Geofisica e Vulcanolgia, Italy
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On August 24, 2016, a Mw 6.0 earthquake hit a sector of the Apennines in Central Italy, causing many damage to the town of Amatrice and several surroundings villages, and killing 299 inhabitants. The earthquake nucleated at a depth of about 8 km, with normal faulting mechanisms striking NW-SE. It was followed by more than 10.000 aftershocks in two months, located southeast and northwest of the hypocentre. An Mw 5.4 aftershock occurred about one hour later and was located 12 km NW of the mainshock near the town of Norcia.
Two important aftershocks then occurred on October 26th, a Mw 5.4 followed by a Mw 5.9 event, in an area located about 20 km North of the August 24 event. However, on October 30th, a stronger earthquake of Mw 6.5 occurred, in the area between the previous events. All the main events of the sequence have similar normal mechanisms.
In this work, we exploit InSAR and GPS measurements to infer the ground displacement and the seismic source parameters of the causative faults of the sequence. We use GPS data recorded by several continuous stations and by few other episodic GPS installed after two days from the August 24 mainshock. Concerning the SAR images, we use a large dataset provided by ALOS-2 (Japanese Aerospace Exploration Agency), Sentinel-1 (European Space Agency) and COSMO-SkyMed (Italian Space Agency) interferometric pairs, from both ascending and descending orbits.
We exploit 13 InSAR displacement maps and more than 80 GPS measurements to model the complex ruptures occurred during the whole sequence, showing the fault slip distributions and discussing the tectonics of the region.
[Authors] [ Overview programme] [ Keywords]
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Paper 295 - Session title: Poster Session 1
Tuesday-9 - GPS water vapour tomographies for DInSAR deformation measurements: application on Mount Etna.
Aranzulla, Massimo (1); Spinetti, Claudia (1); Cannavo', Flavio (1); Guglielmino, Francesco (1); Romaniello, Vito (1); Briole, Pierre (2); Puglisi, Giuseppe (1) 1: Istituto Nazionale di Geofisica e Vulcanologia, Italy; 2: École normale supérieure, Paris
Show abstract
In the framework of the EC FP7 MED-SUV project (call FP7 ENV.2012.6.4-2), we used GPS and multispectral satellite data to reduce atmospheric artefacts in the SAR interferometric images. We carried out a study to improve the accuracy of the ground deformation estimation on Mt. Etna volcano (Italy) by modelling the tropospheric delays. Among various effects affecting the interferograms, atmospheric artefacts are the most significant and difficult to model. Due to the complex orography of Mt. Etna and the highly variable weather conditions, the atmospheric heterogeneities can heavily affect InSAR measurements with extreme values of anomalies, with respect to a standard model, that can reach 100 mm (corresponding to 4 C-band fringes) in some cases. For these reasons, estimating the Mt. Etna atmospheric anomalies is crucial to correct the InSAR measurements. The Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo (INGV-OE) currently monitors the ground deformations of Mt. Etna with a network of 42 permanent GPS stations located over and around the entire volcano edifice. The data collected by the GPS monitoring network have been processed using the GAMIT software, adopting the Vienna Mapping Functions (VMF1) to improve the modelling of the tropospheric delays. A specific software has been developed in order to derive the tomographic imagery of the troposphere over Etna volcano, starting from the tropospheric delays calculated by GPS in all stations of the network. The developed algorithm has been validated by using synthetic tests. These consist of assuming different structures of atmospheric anomalies in the input data and verifying the ability of the algorithm to reproduce them. The test results confirmed the capability of the software to return the simulated anomalies faithfully. With the aim of applying the tomography algorithm to a real case, we introduced the water vapour content estimated by the MODIS instrument on board Terra and Aqua satellites. When the cloud cover permits the use of this data, its addition provides a twofold benefit: it improves the tomographic resolution and adds a feedback for the GPS wet delay measurements. Finally, the tomography algorithm was applied on InSAR Sentinel-1 Interferometric Wide Swath data on Mt. Etna during 2015. In order to reduce the known problem of the correction for the antenna pattern, the interferometric process was performed only on a single burst of one subset of Sentinel-1 IW data. We present the results of this analysis of some 2015 test cases.
[Authors] [ Overview programme] [ Keywords]
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Paper 296 - Session title: Poster Session 1
Tuesday-130 - Fringe change assessment affected by landscape variation (case study X & C bands)
Almodaresi, S.Ali; Mirmansouri, S.Ali; Zarekamali, Mojtaba Islamic azad university, Islamic Republic of Iran
Show abstract
Abstract
Remote sensing technology have used to detect, monitor, mapping natural resources, soil and water Remote sensing have wide applications in many fields of research such as Interferometry and Polarimetric-interferometry applications. Interferometric technique uses to extract information from electromagnetic interference. In this study, 19 images C-band sensor and 11 image s X-band sensors were used and radar differential interferometry technique was studied on the effects of spatial patterns, when Finch in the changing level in two-time series in Tehran that CANNY filter to find Fringe pattern effect and linear profiles were used to find out the pattern of Fringe. This trend were one equation of degree y = 0.0002x - 3.3941 for ENVISAT ASAR sensor with R2 square =0.8575 and equation of y = 0.0002x - 2.311 for Terra SAR sensor with R2 square =0.8069.The effect of this change was small but Fringe in different time intervals was followed the general trend and this pattern to be valid in all this interference Views Finch was affected by factors that cause changes in the phenomenon has been Fringe and this fringe patterns were dynamically in all interferograms. These Influenced by factors causing change in the Fringe phenomenon and this Fringe model has moved in land subsidence direct. Fringe final model of subsidence has formed as a bow that there were quickly rise in bow out.
Keywords: Fringe pattern, linear regression, interferogram, CANNY filter
[Authors] [ Overview programme] [ Keywords]
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Paper 297 - Session title: Poster Session 1
Tuesday-126 - Compare vertical surface displacement using SBAS algorithm case study (X band and C-band)
Almodaresi, S.Ali; Zarekamali, Mojtaba; Mirmansouri, S Ali Islamic Azad University, Islamic Republic of Iran
Show abstract
Crust of the Earth is not constant throughout geological history, but it influenced by internal and external factors these are constantly changing shape. Displacement or collapse especially weak point of the solid earth causes changes in the land. damage caused by these natural human phenomena on the Earth's surface. Synthetic aperture radar interferometry image processing method (INSAR) is widely used to detect small movements of land and changes in land surface have been used. In this study, time series analysis algorithm is a short location length baseline (SBAS) and the technique of differential interferometric synthetic aperture radar (DInSAR) to study the vertical displacement of the Earth's surface was used in Tehran. That 19 images C-band sensor and 11 image s X-band sensors. Interval of time for images listed respectively in 1680 and 187 days respectively. After processing, displacement maps for the whole history of the Earth's surface than was calculated on the original image and map the vertical displacement on the ground was prepared for each sensor calculated. In order to reduce the effect of these variables induced land of agricultural lands, only interferograms with baseline during a short period in time series analysis was created. But in order to reduce the effect of the lack of resolve least squares coefficient matrix rank, contrary to common practice in this area SBAS interferograms high place with over baseline were also analyzed. ASAR sensor mm and 0.777 mm in day to day for the sensor TERRA SAR as well as to uplift areas that have the same process was repeated and the average of 0.529 mm and 0.476 mm ASAR sensor in the day to day for the sensor TERRA SAR
Keywords: Differential Interferometry, SBAS Algorithm, Vertical Displacement, TERRA SAR X BAND, ASAR C BAND
[Authors] [ Overview programme] [ Keywords]
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Paper 299 - Session title: Poster Session 1
Tuesday-149 - 3D displacement maps of the 2016 central Italy seismic sequence, by applying the SISTEM method to GPS and DInSAR data
Guglielmino, Francesco; Bonforte, Alessandro Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, Piazza Roma, 2, 95123 Catania, Italy
Show abstract
We present an application of the SISTEM (Simultaneous and Integrated Strain Tensor Estimation from geodetic and satellite deformation Measurements) approach, to obtain the dense 3D ground deformation pattern produced by 2016 central Italy seismic sequence.
In particular, we analyzed GNSS and InSAR data over the 12 days period from October 20th to November 01st, which includes the co-seismic displacements of the M5.9 and M6.5 events occurred on October 26th and 30th. Ground deformations were clearly recorded by the available SAR images collected across the earthquake, allowing identifying the active fault that produced, at the surface, a maximum coseismic subsidence of ~80cm near the Castelluccio plain. The earthquake of October 30th 2016, characterized by a SW dipping normal fault with thousands of foreshocks and aftershocks located in the depth range 5÷15 km, is the Italian strongest event after the 1980 MW 6.9 Irpinia earthquake
We inverted the SISTEM results using an optimization algorithm based on the Genetic Algorithm, providing an accurate spatial characterization of ground deformation.
Our results improve previous solutions for the principal faults kinematics and, thanks to the unprecedented details provided by SISTEM approach, it was possible to identify the kinematic of other additional faults that activated during the seismic sequence and that have contributed to the observed total ground deformations.
SISTEM results are in good agreement with seismological, geodetic and geological data, including the contribution of the post-seismic signal to the modeled deformation.
[Authors] [ Overview programme] [ Keywords]
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Paper 301 - Session title: Poster Session 1
Tuesday-92 - 3D Displacement Field Estimation Using Sentinel-1
Kourkouli, Penelope; Wegmüller, Urs; Werner, Charles; Magnard, Christophe Gamma Remote Sensing AG, Switzerland
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The last decades, InSAR has shown outstanding progress by monitoring large-scale ground displacements in a wide range of applications, such as earthquakes, landslides and volcanic eruptions. Source geometry in ground motion modeling can be ambiguous when it is derived from vertical component (1D) only (Dieterich & Decker, 1975). Hence, a 3D displacement field permits better resolution of the deformation model parameters for geologic processes. One important limitation of InSAR is that it can measure only in the line of sight (LOS) component of displacement. This can partly be overcome using a combination of ascending and descending acquisitions to get two independent LOS components. Nevertheless, due to the fact that SAR satellites have near-polar orbits, the resolution on the north-south component is still poor (Wright et al., 2004).
Recent advances in SAR technology have lead to the launching of a new generation of sensors devoted to wide-swath imaging. Wide-swath images permit global monitoring with significantly shorter revisit times. The C-band Sentinel-1A/B offer a revisit time of 6-12 days. In our example, the Interferometric Wide swath (IWS) acquisition mode of Sentinel implements a new type of ScanSAR, called Terrain Observation with Progressive Scan (TOPS).
The present paper investigates the potential of estimating the 3D displacement field of seismic events by using Sentinel-1 TOPS data. For a full 3D construction displacement field, we followed an integrated strategy by using LOS measurements from ascending and descending InSAR combined with along-track offsets. With ascending and descending InSAR, two LOS components can be resolved. Furthermore, the along-track component is resolved using either offset tracking or split-beam interferometry (SBI). SBI (Wegmüller et al., 2016) is possible with S1-IWS in spite of strong along-track Doppler variations. The method presented here is based on examples of co-seismic displacements. If more than three components are available, a combination utilizing the quality of the individual observations is used. With this strategy, we derive a full 3D deformation map comparing the precision and the uncertainty of the results with the conventional InSAR. Finally, we discuss both the limitations and potential of this methodology.
References
Dieterich, J.H. and Decker, R.W. (1975). Finite element modeling of surface deformation associated with volcanism. Journal of Geophysical Research 80: doi: 10.1029/JB080i029p04094. Issn: 0148-0227.
Wright, T.J., Parsons, B. E. and Lu, Z. (2004). Toward mapping surface deformation in three dimensions using InSAR, Geophys. Res. Lett., 31, L01607, doi: 10.1029/2003GL018827.
Wegmüller U., Werner, C., Strozzi, T., Wiesmann, A., Frey, O. and Santoro, M. (2016). Sentinel-1 Support in the GAMMA Software. Procedia Computer Science, Vol. 100, pp. 1305-1312.
[Authors] [ Overview programme] [ Keywords]
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Paper 303 - Session title: Poster Session 1
Tuesday-88 - Sentinel-1 Exploitation Solution based on Calibrated Burst Database
Lazecky, Milan (1); Bakon, Matus (2); Hlavacova, Ivana (3); Qin, Yuxiao (4) 1: VSB-TU Ostrava, Czechia; 2: STU Bratislava, Slovakia; 3: GISAT Corp., Prague, Czechia; 4: Purdue University, West Lafayette, USA
Show abstract
A logical step towards a systematic Sentinel-1 exploitation is a more effective way of data storage, ready for a fast processing. Several implementations of the PS InSAR technique (e.g. SARPROZ) demonstrated that interferograms do not necessarily have to be generated prior to the processing, especially if only temporal unwrapping is to be performed in the time series. Our database contains Sentinel-1 bursts that have been preprocessed to the state of a consistent dataset (i.e. after coregistration, calibration and an adapted ESD correction). Based on this, the further processing time is significantly reduced in order to achieve PS or SB-based velocity maps or a result from another exploitation. Every new pre-processed burst can also trigger a processing update that is able to detect unexpected changes in InSAR time series and therefore provide a signal for early warning against suspicious occurrence of a potential dangerous displacements.
The system is developed independently on popular existing frameworks and connects several works licensed in an open way. It is originally intended to generate nation-wide products, such as publicly available PS-based time series of urban areas or an SB-based map of potential landslide activities. Examples are to be provided in the final version of this contribution.
[Authors] [ Overview programme] [ Keywords]
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Paper 306 - Session title: Poster Session 1
Tuesday-70 - Assessment of the Operational Use of SENTINEL 1A/B data in support of Defence and Security mission based on the example of a suspected nuclear related facility
Robin, Jean-Philippe; Górzynska, Maria European Union Satellite Centre, Spain
Show abstract
Remotely sensed data is an essential asset for numerous applications. But it is of utmost importance for regions or countries that could not be visited or where remotely sensed data are actually a unique source of information.
Several countries are suspected of developing nuclear programs with few publicly disclosed details. One of the ways of gathering relevant information about these programs is through the use of commercial and publicly available earth observation sensors. According to open source information, two suspected underground nuclear tests reportedly took place during 2016 in one of these countries. The first event occurred on 6th Jan with the magnitude of 5.1, second – on 9th of Sep, with 5.3. Both events have been registered by the global network of seismic sensors and reported by the USGS scientific agency and the CTBTO international organization. This global sensors network is meant to record natural dynamic geological events, such as earthquakes, which generally trigger disturbances of the upper Earth’s surface such as subsidence, uplifts and/or landslides. Underground nuclear explosions with significant yields are recorded in the same way as earthquakes. Although both types of event share similar effects, each one is characterised by different waveform patterns, making the distinction between the natural and the man-made events possible.
Since seismic events and in particular nuclear underground tests often occur without previous notice, continuous remotely sensed acquisitions are of high relevancy in the perspective of confirming and further assessing the event’s significance. Therefore, an ESA developed COPERNICUS satellite constellation such a Sentinel-1 that provides regular, easily accessible and free of charge Earth coverage, can support operational monitoring needs within the defence and security domain. Moreover, the launch of Sentinel 1B and the resulting decrease of the temporal baseline to 6 days instead of 12, improves not only the valuable temporal resolution important for the defence and security needs, but also the conditions for the further generation of relevant interferometry products.
In its mandate to support the decision making of the European Union Common Security and Defence Policy (CSDP), which includes the surveillance of suspected proliferating installations, the European Union Satellite Centre provides Geospatial Intelligence analysis and products based on a wide range of space-borne sensors (optical and radar). In this perspective, the following paper aims to assess the usefulness of Sentinel 1 SAR data in support of Defence and Security applications such as monitoring of nuclear related facilities.
Various pre- and post- event scenes in interferometric conditions have been processed in order to generate various interferometric products. The scenes used for the work were selected from the Sentinel-1 COPERNICUS catalogue, with the IW acquisition mode (TOPSAR), that allowed output products with an approximate projected resolution of 15 m in which indicators of underground explosions have been investigated. In addition to the technical approach, the location of interest provides numerous challenges as it covers a small, highly vegetated mountainous area of just a few hectares, comprising very few man-made features. According to open source information, the tunnels in which the test explosions were conducted are located underneath the mountain slopes. Explosions of such nature and magnitude often result in changes of the surface (such as subsidence or landslide) and therefore should be detectable by interferometry means. Prior to the use of Differential Interferometry techniques aimed at detecting ground motion, additional methods widely applied within security and defence domain, such as ACD (Amplitude Change Detection), CCD (Coherence Change Detection) or MTC (Multi Temporal Coherence) have been employed on the datasets in order to complement and better assess possible usefulness of Sentinel-1 data for the provision of relevant information.
Finally, depending on the availability of the post-event Sentinel-1 StripMap data, the research also investigates on the potential added value of using higher resolution data for this purpose.
[Authors] [ Overview programme] [ Keywords]
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Paper 311 - Session title: Poster Session 1
Tuesday-150 - On the 2016 Central Italy seismic sequence governing scenario investigated via DInSAR and geological data integration
Valerio, Emanuela (1); Bonano, Manuela (2); Carminati, Eugenio (1); Castaldo, Raffaele (2); Casu, Francesco (2); De Luca, Claudio (2); De Novellis, Vincenzo (2); Doglioni, Carlo (1,3); Lanari, Riccardo (2); Manunta, Michele (2); Manzo, Mariarosaria (2); Pepe, Susi (2); Solaro, Giuseppe (2); Tizzani, Pietro (2); Zinno, Ivana (2) 1: Sapienza University of Rome, Italy; 2: National Research Council (CNR), Istituto per il Rilevamento Elettromagnetico dell’Ambiente (IREA), Napoli, Italy; 3: National Institute of Geophysics and Volcanology (INGV), Rome, Italy
Show abstract
We investigate the ground deformation pattern and the source geometry responsible of the 2016 Central Italy seismic sequence (CISS) by joint exploiting the Multisensors and Multiorbits satellite measurements (i.e. Sentinel-1 and ALOS 2) and the integration with the available geological/structural and seismological data. To this purpose we integrate these measurements in a physically-based optimization model scenario.
We consider the new seismic sequence that struck Umbria-Marche Apennines (Central Italy) since the month of August 2016. This seismic sequence started with the Amatrice earthquake (MW 6.0) occurred on August 24th. This event nucleated along a SW dipping extensional lineament, called the Mt. Gorzano fault (e.g. Boncio et al., 2004), and caused 299 casualties and severe damages to buildings and historical monuments, devastating Amatrice itself, Accumoli and other surrounding small towns. During the following months, very numerous aftershocks have nucleated and the CISS has migrated northward (e.g. Tinti et al., 2016). On October 26th two intense events occurred with ML 5.4 and ML 5.9, respectively. Moreover, on October 30th the strongest event of the sequence occurred with MW 6.5 close to the small town of Norcia and nucleated along the Mt. Vettore extensional fault (e.g. Galadini & Galli, 2003). The involved area is still active and a lot of earthquake nucleate every day: up to now, the INGV seismic network has recorded more than 30000 events.
Despite to the tectonic complexity of the 2016 CISS, we achieved a good determination/description of the ground deformation pattern thanks to the big amount of SAR data acquired by Sentinel-1 (ESA) and ALOS 2 (JAXA) satellites, characterized by small temporal baselines and from different orbits (ascending and descending orbits). In this way, we can analyse in greater detail the ground deformation pattern of the individual seismic events, also decomposing the vertical component and the east-west one. In this context SAR data are a fundamental tool to better understand the spatio-temporal evolution of 2016 CISS.
In this context, the present study, benefiting from satellite and in situ information, will investigate, through a numerical optimization multiphysics approach, the most suitable geological scenario that governed the spatial and temporal evolution of the Amatrice-Norcia seismic sequence.
References
Boncio, P., Lavecchia, G., Milana, G., & Rozzi, B. (2004). “Seismogenesis in Central Apennines, Italy: an integrated analysis of minor earthquake sequences and structural data in the Amatrice-Campotosto area.” Annals of Geophysics, vol. 47, issue 6, December 2004.
Galadini, F., & Galli, P. (2003). “Paleoseismology of silent faults in the Central Apennines (Italy): the Mt. Vettore and Laga Mts. faults.” Annals of Geophysics, vol. 46, issue 5, October 2003.
Tinti, E., Scognamiglio, L., Michelini, A., & Cocco, M. (2016). “Slip heterogeneity and directivity of the ML 6.0, 2016, Amatrice earthquake estimated with rapid finite‐fault inversion.” Geophysical Research Letters, vol. 43, issue 20.
[Authors] [ Overview programme] [ Keywords]
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Paper 313 - Session title: Poster Session 1
Tuesday-135 - Mitigation of topographic phase in multi-temporal InSAR by integer combination
Zhang, Lei; Ding, Xiaoli; Liang, Hongyu; Wu, Songbo The Hong Kong Polytechnic University, Hong Kong S.A.R. (China)
Show abstract
Interferometric phase is a mixture of components contributed by topography, deformation, orbit error, atmospheric artifacts, integer ambiguities and noise. When deformation is a signal of interests, differential operation with external DEM is conventionally conducted to mitigate the topographic phase. However with the increasing spatial resolution of SAR images, the external DEM is becoming less and less qualified for this purpose, resulting in notable phase residues and even decorrelation in differential interferograms. Even worse situation can be seen in urban areas, especially in developing countries undergoing rapid urbanization, where no updated DEM with fine resolution is timely available. Although topographic phase residual can be parameterized and estimated by current multi-temporal InSAR (MTInSAR) techniques, as summarized by Du et al. (2016), its accuracy is limited by several factor, e.g., the baseline threshold and diversity, improper deformation model, interferogram network connectivity and noise. Considering that the phase contribution of topography is controlled by both height and perpendicular baselines, instead of providing accurate height information, an alternative way for DEM phase mitigation is to shorten the length of baselines. Thanks to excellent control of satellite status, interferograms generated by some modern satellite radars (e..g, TerraSAR-X and Sentinel-1A/B) can own extremely short baselines, where the DEM phase can be safely ignored. Unfortunately the number of such interferograms can never be guaranteed. We attempt here to generate a set of pseudo interferograms with near-zero baselines by a strategy termed integer combination proposed by Massonnet (1996) and then take these pseudo interferograms as observations of MTInSAR model, where deformation becomes the only signal needs to be parameterized. By doing this, external DEM is no longer needed in the MTInSAR processing chain and the number of parameters is reduced, leading to an improved estimation of deformation time series. Semi-synthetic tests and real datasets are used to validate the proposed method. As expected, its performance is quite satisfied.
References:
Du, Y.N., Zhang, L., Feng, G.C., Lu, Z., and Sun, Q. (2016). On the accuracy of topographic residuals retrieved by MTInSAR. IEEE Transactions on Geoscience and Remote Sensing, 99, 1-13.
Massonnet, D., Vadon, H., Rossi, M. (1996). Reduction of the Need for Phase Unwrapping in Radar Interferometry, IEEE Transactions on Geoscience and Remote Sensing, 34(2) 489–497
[Authors] [ Overview programme] [ Keywords]
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Paper 319 - Session title: Poster Session 1
Tuesday-124 - Automatic identification of subsidence patterns in Sentinel-1 interferograms
Porzycka-Strzelczyk, Stanisława (1); Dwornik, Maciej (2); Strzelczyk, Jacek (1); Murdzek, Radosław (1) 1: AGH University of Science and Technology, SATIM Satellite Monitoring; 2: AGH University of Science and Technology
Show abstract
One of the most characteristic type of ground subsidence is caused by underground coal exploitation. The resultant surface effect, called subsidence trough, has usually a form of depression in the ground with more or less elliptical or circular shape. The largest values of vertical displacements occur in the centre of trough and progressively decrease towards its edges. Those deformations can cause damages to surface and subsurface infrastructure. Therefore, their detection and permanent monitoring is essential to ensure safety within mining and postmining areas. Subsidence troughs are represented on the SAR interferograms by elliptical or circular interferometric fringes thickening in the direction of centre of trough. Since the deformations can also occur within areas that exhibit, in whole or in part, low coherence of SAR images, the subsidence trough may be invisible or only partially visible on interferogram.
In this paper the method for automatic detection of subsidence troughs on SAR interferograms is proposed. This procedure is mainly limited by non-elliptical shapes of subsidence patterns, overlapped regions or low Signal-Noise Ratio (SNR). In order to speed up detection the proposed algorithm consists of two stages. In the first stage the potential areas of subsidence troughs occurrence are identified. Afterwards, the verification of those areas is performed. The proposed method was tested for interferograms obtained based on SAR images acquired from Sentinel-1A satellite.
[Authors] [ Overview programme] [ Keywords]
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Paper 320 - Session title: Poster Session 1
Tuesday-33 - ESA Research and Service Support: making easier the Sentinel-1 data exploitation
Delgado Blasco, Jose Manuel (1,2); Cuccu, Roberto (1,2); Arcorace, Mauro (1,2); De Luca, Claudio (3); Casu, Francesco (3); Foumelis, Michael (4); Rivolta, Giancarlo (1,2); Sabatino, Giovanni (1,2) 1: ESA Research and Service Support, via Galileo Galilei, 1, 00044 Frascati (Italy); 2: Progressive Systems Srl, Parco Scientifico di Tor Vergata, 00133 Roma (Italy); 3: IREA-CNR, Via Diocleziano 328, 80124, Napoli, Italy; 4: Earth Observation/Science, European Space Agency, via Galileo Galilei, 1, 00044 Frascati (Italy)
Show abstract
Already immerse in the Sentinel era, the ESA Research and Service Support (RSS) offers several services to make it easier for users and researchers to get original and processed Sentinel-1 data. The ESA RSS offers several service solutions to make bulk data processing using consolidated algorithms and algorithm development/testing as well.
The RSS service offer is composed of several elements supporting different phases of the research process flow. It includes e-collaboration environments to find and share information, reference and sample datasets, access to a huge EO data archive without the need to download on scientist or developer “own” resources, customised cloud toolboxes where scientists and developers alike can fine-tune their algorithms on selected datasets, on-demand processing environment where fine-tuned algorithms can be integrated and made available as EO applications for on-demand massive processing, and results visualization tools.
As an example of consolidated algorithm, the ESA RSS is offering services in its on-demand environment for manipulating the Sentinel-1 data to provide calibrated Sentinel-1 products and TOPSAR interferometric products. This service is based on the ESA open source software Sentinel Application Platform (SNAP), which includes the Sentinel-1 Toolbox. In addition RSS provides a GeoHazards Exploitation Platform (GEP) service demonstrator based on the P-SBAS algorithm of CNR-IREA, until the readiness of the GEP infrastructure scheduled on early 2017.
Such on-demand services have been successfully exploited at times of the several earthquakes that occurred in 2015 and 2016 in Nepal, Chile and Italy as well by proving the RSS capabilities of supporting rapid response to natural disasters.
In addition, the RSS CloudToolbox service offers to users Virtual Machines (VMs) with flexible resources to work with Sentinels data, being the perfect solution for researchers and SME working in the algorithm development/testing and also for researchers with the need of scaling up the available processing resources for achieving their projects objectives. In the frame of this service, a support example is the Sentinel-1 data processing, using both calibrated amplitude and interferometric coherence for the analysis of water variations on Poyang Lake (China) on the frame of ESA’s Dragon III project.
Using this not exhaustive list of services offered by the ESA RSS, the researchers obtain benefit in terms of productivity, storage space saving, timing and processing costs inherent to the research process.
[Authors] [ Overview programme] [ Keywords]
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Paper 321 - Session title: Poster Session 1
Tuesday-97 - 3-D movement mapping of the Siachen glacier by integrating D-InSAR and MAI applying ascending and descending passes in Himalayas
Jiang, Liming (1,2); Li, Daan (1,2); Sun, Qishi (1,2); Wang, Hansheng (1) 1: Institute of Geodesy and Geophysics, CAS, Wuhan, China, People's Republic of; 2: University of Chinese Academy of Sciences, Beijing, China, People's Republic of
Show abstract
In many researches single satellite-based interferometric radar to measure the flow velocity of a large region of glacier. Since single-track interferometric measurements are sensitive to only a single LOS component of the three dimensional (3-D) velocity vectors. Glaciers in the Himalayan region maintain excellent coherence of SAR return signals in one-day temporal difference. European Remote Sensing satellites (ERS-1/2) tandem mission data in ascending and descending tracks provide a method to calculation the three velocity components under the assumption that glacier flow is parallel to its surface.
In this study, we aim to yield an optimal 3-D solution, a variance component estimation algorithm is applied to weigh the D-InSAR and MAI measurements derived from (ERS-1/2) tandem mission data under the scheme of weighted least squares adjustment without the assumption about sloped flow surface. By exploiting the InSAR measurements themselves to determine the weights iteratively, the presented approach results in an accuracy of centimeter to decimeter for all the three velocity vectors. The east-west component shows that the main tributary streams in the Siachen glacier and The north-south component represents flowing from the central area of the main stream to its surroundings. The glacier thickening or thinning is resolved from the vertical component by subtracting the downslope movement. The preliminary results show that the accuracy of surface velocities estimated with the scheme of weighted least squares adjustment are approximately 2cm, 4cm and 8cm in vertical east-west or north-south orientation of three dimension flow direction of the glacier. A maximum 3-D velocity of 65 cm/day has been observed in the tributary streams intersection area. The results of 3-D ice stream can be used as a good indication of the ice dynamics monitoring and the mass balance calculation.
[Authors] [ Overview programme] [ Keywords]
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Paper 328 - Session title: Poster Session 1
Tuesday-94 - Bistatic SAR imagery with Sentinel-1A/B for repeat-pass interferometry
Anghel, Andrei (1); Cacoveanu, Remus (1); Moldovan, Adrian-Septimiu (2); Datcu, Mihai (1,3) 1: University Politehnica of Bucharest, Romania; 2: Terrasigna, Romania; 3: DLR, Germany
Show abstract
Bistatic synthetic aperture radar (SAR) systems with a satellite transmitter of opportunity and a fixed ground receiver have recently gained attention due to several reasons: the angular diversity provided by the opportunity of exploiting more acquisition geometries, the possibility to use as transmitters of opportunity different satellites on various orbits, the new perspectives regarding target characterization (e.g., bistatic scattering signature, multiple line of sights for displacements estimation).
In this work we present a bistatic SAR imaging methodology for repeat-pass interferometry applications. The processing flow is designed to work with the Sentinel-1A/B satellites operating in Terrain Observation with Progressive Scans SAR (TOPSAR) mode. The proposed method mainly consists in the synchronization between the satellite transmitter and fixed ground receiver followed by the bistatic focusing and interferograms generation algorithms. Compared to works on bistatic imaging with Sentinel-1 as transmitter of opportunity, the developed processing chain employs GPS-based time/frequency synchronization and exploits the ancillary data of Sentinel-1 (provided with the monostatic product available online) to generate in a direct manner bistatic SAR images suitable for repeat-pass interferometry.
The methodology is applied on a bistatic SAR receiver developed at the University Politehnica of Bucharest in collaboration with the Terrasigna company. The fixed ground platform has two channels -one that receives directly the transmitted pulses through an antenna oriented towards the satellite (reference channel) and another channel that receives the reflected signals through an antenna pointing towards the imaged scene (imaging channel). The synchronization procedure is divided in three parts (timing, frequency and position synchronization).
Timing synchronization refers to the acquisition start time instants. The approximate GPS time and the azimuth/elevation angles corresponding to the closest approach between satellite and ground receiver can be estimated using an orbit propagation model. The reference channel antenna is pointed towards the satellite and the acquisition window is triggered by an amplitude threshold, which means that each sampling window is linked to a received pulse. The GPS timestamp of each trigger is recorded for further processing.
The frequency synchronization addresses the fact that in bistatic systems the demodulated received signal has a certain offset due to the lack of synchronization between the local oscillators (LOs) of the spaceborne and ground platforms. To minimize these effects, the ground platform is disciplined with a GPS receiver. In this way, the ground oscillator’s frequency will have a very stable reference given by the GPS clock. In the literature it is mentioned that the frequency offset between the two oscillators can be estimated from the phase of the pulses received on the reference channel and included in the matched filter function used for range compression. However, it can be shown that the frequency offset correction is not essential for offsets of tens of Hz. Moreover, for repeat-pass interferometry, the frequency offsets in consecutive passes will be more or less the same, since both oscillators are very stable. Hence, the frequency offset will be mainly eliminated as a systematic error and its estimation is not actually mandatory.
Position synchronization consists in determining for each pulse received by the ground platform, the position vector of the satellite when the respective pulse was transmitted. The standard mode of operation of the Sentinel-1 satellites is TOPSAR, which essentially means that the antenna beam is electronically commuted between three sub-swaths in range and is steered during the illumination of a sub-swath from back to forth. This imaging mode adds some difficulties in determining the positions of the satellite corresponding to the moments when the ground-received pulses are transmitted (e.g., a given target on the ground may not be illuminated by the satellite at the point of closest approach like in strip-map mode). For TOPSAR illumination, we developed a position synchronization method based on the GPS timestamps recorded for each triggered pulse by the ground platform and the transmission timestamps annotated in the ancillary data of the corresponding monostatic acquisition. For all transmitted pulses, we compute an estimate of the ground timestamp considering the propagation delay in vacuum. Each pulse received by the ground platform has an associated triggering timestamp measured by GPS. A received pulse can be linked with the corresponding transmitted pulse by minimizing the absolute difference between the estimated and measured timestamps. The position vector of the satellite when each received pulse was transmitted is computed by interpolating the state vectors of the ancillary data. In this way, the satellite position vectors are determined without an orbit propagation model, which can introduce errors of hundreds of meters. These errors may not have a large impact in ranging, but they can affect the phase for repeat-pass interferometric applications, since they are not systematic (like the ground receiver positioning error or the delays on the two receive channels).
Due to the amplitude-based triggering, the ground receiver stores from each burst only the pulses that reach at some point the triggering threshold. Hence most of the pulses are received in groups of consecutive pulses situated more or less around a pulse with maximum amplitude where the antenna beam is pointing towards the ground receiver. Therefore, from the synchronized data we have to extract groups of consecutive pulses that are used as input in the focusing algorithm (each group generates a single image).
The azimuth focusing of the selected pulses is performed using a back-projection algorithm. For repeat-pass interferometry, the groups of pulses from each pass have to be selected such that they cover the same spatial azimuth interval as the master acquisition. In this way the common band filtering operation is actually performed before azimuth focusing. The focused images are co-registered (by shifting according to the inter-correlation peak) and the interferograms are generated as multi-look coherence phase maps.
The first bistatic SAR images and interferograms obtained with Sentinel-1A/B over an area of Bucharest city shall be presented at the workshop. Additionally, the developed imaging methodology will be assessed using the bistatic InSAR results.
This work has been funded by ESA through the ”Opportunistic C band bistatic SAR differential interferometry” (COBIS) project, ESA Contract No. 4000115608/15/NL/CBi.
[Authors] [ Overview programme] [ Keywords]
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Paper 332 - Session title: Poster Session 1
Tuesday-14 - Interferometric and polarimetric end-to-end simulator for low-frequency SAR missions
Mancon, Simone; Giudici, Davide; Giorgi, Emanuele; Mapelli, Daniele; Recchia, Andrea ARESYS, Italy
Show abstract
Low frequency spaceborne SARs (operating at L and P band) are attracting more and more interest from the scientific community, thanks to the peculiar properties of such bands, like penetration and long term coherence.
Recently, the development of the next ESA Earth Explorer Mission BIOMASS, and the investigations about a possible passive Companion satellite to the Argentinean satellite SAOCOM-1B, have even increased the interest and opened new challenges at system and processing level.
The limited amount of existing data makes simulation a key tool for investigation of the technical solutions and the performance assessment.
In the paper we describe an end-to-end data simulation approach particularly focused on low-frequency SAR missions. The key aspects are the simulation of the ionospheric disturbances and the consideration of the 3-D distribution of the scatterers. Accurate modeling of the wave-target interaction for all the polarizations is included.
The realistic speckle simulation allows to generate accurate interferometric datasets and to assess performance parameters at L0, L1 and L2.
We show sample results considering the case of the SAOCOM-CS to demonstrate the simulation approach capability and do a first prediction of the achievable performances of the mission, particularly focusing on the tomographic phase.
[Authors] [ Overview programme] [ Keywords]
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Paper 336 - Session title: Poster Session 1
Tuesday-101 - Elevation change over mountain and valley glaciers in the Maipo Basin, Central Andes, Chile.
Farias, David (1); Seehaus, Thorsten (1); Vivero, Sebatian (2); Braun, Matthias H. (1); Casassa, Gino (3,4) 1: Institute of Geography and Geosciences, Friedrich Alexander Universität Erlangen-Nürnberg, Germany; 2: Institute of Earth Surface Dynamics (IDYST), University of Lausanne, Switzerland; 3: Geoestudios, Santiago, Chile; 4: Universidad de Magallanes, Punta Arenas, Chile.
Show abstract
The Maipo basin (33° S, 70° W, 15.274 km²) is located in Central Andes and comprises Santiago, the capital of Chile. The basin is Mediterranean climate with marked winter and summer seasons, large mountain and valley glaciers are found in this basin, and they are sensitive to inter-annual variations in temperature and precipitation (el Niño Southern Oscillation, ENSO). The Maipo basin is the main glacierized area of Chile outside Patagonia. Where the last Chilean glacier inventory revealed a glacier extent of about 397.6 km2 distributed over 1009 glaciers larger than 0.01 km2. The glaciers located in this basin represent 2% the total glacierized area in Chile. The 1009 glaciers in the Maipo basin, compose of 708 rock glaciers (159.91 km2), 126 glaciarets (5.85 km2) and 175 valley and mountain glaciers (231.84 km2). Our focus in this study is to evaluate the suitability of TanDEM-X to derive in geodetic glacier mass balance on small mountain glaciers. Our database comprises digital elevation models (DEM) from historical cartography based on aerial photographs (1955), SRTM (2000), Lidar data (2015) and TanDEM-X. The historical cartography was scanned and georeferenced with the aid of several GCPs derived from the Lidar dataset. The TanDEM-X data was processed using differential interferometry by SRTM C-band DEM as reference. Differences resulting from X- and C-band penetration are considered comparing X- and C-band SRTM data. All DEMs were horizontal and vertically co-registered to each other. Error assessment was done over stable ground. Our preliminary result indicate an elevation change of -42.2 m ± 4 m (1955-2015) for Echaurren Norte Glacier. The estimated averaged annual elevation change is -0.7 m for the period 1955-2015.
[Authors] [ Overview programme] [ Keywords]
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Paper 338 - Session title: Poster Session 1
Tuesday-102 - Geodetic Mass Balance From TanDEM-X In The Southern Andes, Patagonia
Malz, Philipp (1); Jaña, Ricardo (2); Weidemann, Stephanie (3); Casassa, Gino (4); Braun, Matthias (1) 1: Friedrich Alexander Universität Erlangen-Nürnberg, Germany; 2: Instituto Antártico Chileno - INACH, Punta Arenas, Chile; 3: RWTH Aachen University, Aachen, Germany; 4: University of Magallanes, Punta Arenas, Chile
Show abstract
The Patagonian Ice Fields are one of the largest connected ice-bodies outside of the polar ice sheets. They show one of the highest mass loss rates compared to their size. This implies a better knowledge and quantification of the ongoing changes. The geodetic mass balances are derived by SAR interferometry using the SRTM C-band DEM as reference and repeat TanDEM-X data between 2011 and 2015. The bistatic TanDEM-X data is processed using a differential interferometric approach in order to minimize the influence of the rough terrain on the phase unwrapping. Since the TanDEM-X data covers different seasons it allows for analysis of multi-year changes but also for seasonal differences and influence of radar penetration.
We do quality assessment based on stable ground but also incorporate differential Global Navigation Satellite System measurements on Grey Glacier from 2015. The results show a large variation in geodetic mass balances. We observe an altitude dependence of the elevation changes, whereas a clear east-west pattern could not be distinguished. The elevation change rates reach a maximum of 8 m per year. The mass loss amounts to 21 Gt (2000-2014) for the SPI area south of 50.3° S.
[Authors] [ Overview programme] [ Keywords]
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Paper 348 - Session title: Poster Session 1
Tuesday-134 - Massive exploitation of SAR archives for Vertical and East-West deformation components evaluation of wide areas.
De Luca, Claudio; Zinno, Ivana; Manunta, Michele; Lanari, Riccardo; Casu, Francesco IREA-CNR, Via Diocleziano 328, 80124, Napoli, Italy
Show abstract
Massive exploitation of SAR archives for Vertical and East-West deformation components evaluation of wide areas.
Claudio De Luca, Ivana Zinno, Michele Manunta, Riccardo Lanari, Francesco Casu
IREA-CNR, Via Diocleziano 328, 80124, Napoli, Italy
Keywords: DInSAR, P-SBAS, Cloud Computing, Mosaicking, ENVISAT, Sentinel-1
In this work we present a methodology for generating the Vertical and Horizontal (East-West) components of Earth’s surface deformation at large spatial scale. In particular, it relies on the availability of a set of SAR data collected over an Area of Interest (AoI), which could be some hundreads of thousands of square kilometers wide, from ascending and descending orbits.
The exploited SAR data are processed, on a frame basis, through an Advanced Differential SAR Interferometry (DInSAR) approach thus finally generating the displacement time series and the corresponding mean deformation velocity maps. In our case we use the Parallel version of the Small BAseline Subset (P-SBAS) DInSAR chain [3,4], which allows the unsupervised processing of large SAR data volumes, from the raw data (level-0) imagery up to the generation of the DInSAR time series and the mean deformation velocity maps, by exploiting distributed computing resources (e.g. Cloud Computing) to enhance the processing speed.
Subsequently, starting from the so generated DInSAR results, the proposed methodology lays on a proper mosaicking procedure to finally retrieve the mean velocity maps of the Vertical and Horizontal (East-West) deformation components relevant to the overall AoI.
To achieve this task, the overall area covered by the P-SBAS deformation velocities is divided in a regular grid of N boxes characterized by the same spatial extent (as depicted in Fig.1 (a) for a very small area), and with an overlap with the adjacent ones along both the East and North directions (see Fig.1 (a)). Obviously, the size of the boxes can be adapted to the footprint of the satellite tracks relevant to the analyzed data set. Because each box is imaged by different SAR tracks (see Fig.1 (b)) it is possible to compute, for those boxes covered by at least one ascending and one descending track, the Vertical and Horizontal (East-West) components of the displacement velocity [5-7]. To this aim, as pictorially shown in Fig.1 (b), we consider all the generated deformation velocity maps relevant to the slices that cover, also partially, the considered box.
Furthermore, the described mosaicking procedure is totally automatic and allows also the usage of GPS measurements, which permit to both account for possible regional trends not easily detectable by DInSAR analyses, and to refer the P-SBAS measurements to an external geodetic datum.
We tested the proposed methodology with the ENVISAT ASAR archives that have been acquired, from ascending and descending orbits, over Southern California (US), covering an area of about 90.000 km2. Such an input dataset has been processed in parallel and in automatic way, through the P-SBAS algorithm, by exploiting 280 computing nodes of the Amazon Web Services Cloud environment. Subsequently the achieved results have been mosaicked as previously described. The results demonstrate the effectiveness of the proposed approach for the large-scale estimation of the deformation components, as shown in Fig.2 and Fig.3.
It is worth noting that such methodology could be useful for an extensive exploitation of the first-generation SAR data archives (firstly ERS-1/2 and ENVISAT), which have been only partially explored during the past years, and then may represent a key element for the comprehension of the Earth's surface dynamics of large areas. Therefore, it is not surprising that some relevant efforts in this direction have been already carried out [8]
Furthermore, the presented methodology can be easily applied also to other SAR satellite data. Above all, it is particularly suitable to deal with the very large data flow provided by the Sentinel-1 constellation [9], which collects data with a global coverage policy and an acquisition mode specifically designed for interferometric applications.
Finally, due to the constant temporal sampling of the Sentinel-1 constellation (down to 6 days in some regions of Earth), it will be also possible to extend the proposed mosaicking procedure to generate Vertical and Horizontal displacement time-series.
References
[1]Burgmann R., Rosen P. A., and Fielding E. J., "Synthetic aperture radar interferometry to measure Earth's surface topography and its deformation, " Annu. Rev. Earth Planet. Sci., vol. 28, pp. 169–209, May 2000.
[2]Massonnet D. and Feigl K. L., "Radar Interferometry and its application to changes in the Earth’s surface," Rev. of Geophys., vol. 36, pp. 441–500, 1998.
[3]Casu F., Elefante S., Imperatore P., Zinno I., Manunta M., De Luca C., Lanari R., "SBAS-DInSAR Parallel Processing for Deformation Time-Series Computation," Selected Topics in Applied Earth Observations and Remote Sensing, IEEE Journal of , vol.7, no.8, pp.3285,3296, Aug. 2014.
[4]Zinno I., Mossucca L., Elefante S., De Luca C., Casola V., Terzo O., Casu F., Lanari R., “Cloud Computing for Earth Surface Deformation Analysis via Spaceborne Radar Imaging: a Case Study,” IEEE Trans. Cloud Computing, Vol. 4, pp. 104-118, 2015. doi: 10.1109/TCC.2015.2440267.
[5]Casu F. and Manconi A., “Four-dimensional surface evolution of active rifting from spaceborne SAR data,” Geosphere, GES01225.1, first published on April 7, 2016, doi:10.1130/GES01225.1
[6]Lundgren P., Casu F., Manzo M., Pepe A., Berardino P., Sansosti E., Lanari R., “Gravity and magma induced spreading of Mount Etna volcano revealed by satellite radar interferometry,” Geophysical Research Letters, Vol. 31, Is. 4, 2004, doi 10.1029/2003GL018736
[7]Manzo M., Ricciardi G.P., Casu F., Ventura G., Zeni G., Borgström S., Berardino P., Del Gaudio C., Lanari R., Surface deformation analysis in the Ischia Island (Italy) based on spaceborne radar interferometry, Journal of Volcanology and Geothermal Research, Volume 151, Issue 4, 15 March 2006, Pages 399-416, ISSN 0377-0273
[8]Adam N., Gonzalez F.R., Parizzi A. and Brcic R., "Wide area Persistent Scatterer Interferometry: Current developments, algorithms and examples," 2013 IEEE International Geoscience and Remote Sensing Symposium - IGARSS, Melbourne, VIC, 2013, pp. 1857-1860.
[9]Salvi S., Stramondo S., Funning G.J., Ferretti A., Sarti F. and Mouratidis A., "The Sentinel-1 mission for the improvement of the scientific understanding and the operational monitoring of the seismic cycle,"Remote Sens. Environ., vol. 120, pp. 164–174, May 2012.
[Authors] [ Overview programme] [ Keywords]
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Paper 349 - Session title: Poster Session 1
Tuesday-68 - Added-value of Sentinel-1 interferometric coherence for automatic detection of human settlements
Corbane, Christina; Pesaresi, Martino; Kemper, Thomas; Lemoine, Guido; Sabo, Filip; Syrris, Vasileios European Commision, Italy
Show abstract
Large scale characterization of cities and urbanized areas is essential for monitoring the key processes in urban planning and economic development and is needed for evaluating the efficiency of policy measures. Free and open earth observation data (e.g. Landsat, Sentinel) offer a great potential for large area mapping of human settlements. The Global Human Settlement Layer (GHSL) is the first open and free information layer describing the spatial evolution of human settlements in the past 40 years. It has been produced from Landsat image collections (1975, 1990, 2000 and 2014) and publicly released on the JRC open data portal[1], [2]. The availability of Sentinel-1 can provide up-to-date global information on the status and evolution of human settlements and allow regular updates as well as incremental improvements of the GHSL- Landsat. Recently a new layer describing human settlements at the global level has been produced using worldwide monotemporal coverage of Sentinel-1 Ground Range Detected (GRD) data [3]. The technology at the core of the GHSL-Landsat and Sentinel-1 derived human settlements products is the Symbolic Machine Learning technique (SML) [4]. This new generic supervised classification framework proved to be suitable for Big Earth observation data analytics [5]. Despite the noticeable improvements gained from the increased spatial detail and from the thematic contents of Sentinel-1 amplitude compared to the Landsat derived product, some challenges remained. They stem, to a large extent, from the under-detection of some sparse rural settlements or from commission errors in fields with rough bare soils or with high soil moisture content. Several studies have demonstrated that C-band coherence over short time intervals (1-day, 6-days) contains information on land use classes such as forest, water and especially on urban areas [6].
Hence to overcome the challenges identified in the global product derived from Sentinel-1 we considered the short time interval provided by the combination of Sentine-1A and Sentinel-1B data for calculating the interferometric coherence: the experiment consisted in testing the potential of combining interferometric coherence with the amplitude change between the two scenes of the interferometric pair within the SML framework. This test is based on the assumption that within this short time interval, built-up areas would be characterized by high coherence values and by large coherence contrast to bare soils. This assumption was tested over a test site encompassing Amsterdam and Rotterdam with a Sentinel-1 A and B pair acquired in 12-10-2016 and 18-10-2016 respectively.
The outputs of the GHSL-Landsat, Sentinel-1 GRD and Sentinel-1 “coherence” were compared and validated with reference building footprints covering an area of 1846.5 km2. Several performance metrics were calculated including the correlation of built-up densities derived from the three products describing built-up areas.
The results showed that noticeable improvements can be gained through the combined use of interferometric coherence with the amplitude change within the SML workflow. The correlation coefficients of built-up densities derived from the three products in relation to the reference building footprints were as follows: 0.80 for GHSL-Landsat, 0.84 for Sentinel-1 GRD and 0.89 for Sentinel-1 “coherence”. In terms of overall accuracy (OA), higher values were obtained with Sentinel-1 “coherence”(OA = 0.90) compared to Sentinel-1 GRD (OA = 0.79) and GHSL-Landsat (OA = 0.76). The transferability of the approach was verified in a problematic area North-East of New Delhi where small villages surrounded by agricultural lands were undetected with Landsat and Sentinel-1 GRD data. The ingestion of the coherence product within the SML workflow allowed a better detection of the small rural settlements. The results achieved so far with Sentinel-1 interferometric coherence are very promising, suggesting the possibility of exploiting the coherence feature for a better discrimination of human settlements.
References:
[1] M. Pesaresi, M. Melchiorri, A. Siragusa, and T. Kemper, “Atlas of the Human Planet - Mapping Human Presence on Earth with the Global Human Settlement Layer,” European Commission, DG JRC, Luxembourg (Luxembourg), JRC103150, 2016.
[2] M. Pesaresi. et al., Operating procedure for the production of the Global Human Settlement Layer from Landsat data of the epochs 1975, 1990, 2000, and 2014. Publications Office of the European Union, 2016.
[3] M. Pesaresi, C. Corbane, A. Julea, A. Florczyk, V. Syrris, and P. Soille, “Assessment of the Added-Value of Sentinel-2 for Detecting Built-up Areas,” Remote Sens., vol. 8, no. 4, p. 299, Apr. 2016.
[4] M. Pesaresi, V. Syrris, and A. Julea, “A New Method for Earth Observation Data Analytics Based on Symbolic Machine Learning,” Remote Sens., vol. 8, no. 5, p. 399, May 2016.
[5] M. Pesaresi, S. Vasileios, and A. Julea, “Analyzing big remote sensing data via symbolic machine learning.,” in Proceedings of the 2016 conference on Big Data from Space (BiDS’16), 2016, pp. 156–159.
[6] J. I. H. Askne and M. Santoro, “Automatic Model-Based Estimation of Boreal Forest Stem Volume From Repeat Pass C-band InSAR Coherence,” IEEE Trans. Geosci. Remote Sens., vol. 47, no. 2, pp. 513–516, Feb. 2009.
[Authors] [ Overview programme] [ Keywords]
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Paper 350 - Session title: Poster Session 1
Tuesday-77 - Data Driven Slope-Adaptive Range Common-Band Filter
Leinss, Silvan (1); Hajnsek, Irena (1,2) 1: ETH Zürich, Switzerland; 2: DLR Oberpfaffenhofen
Show abstract
SAR interferograms, especially interferograms acquired with large baselines, are affected by geometric or baseline decorrelation [1]. This results in coherence reduction due to the wavenumber shift in SAR interferometry [2]. For flat terrain, the coherence reduction is proportional to the perpendicular interferometric baseline. However, for terrain with strong topography the coherence reduction is larger for slopes facing towards the radar and smaller for slopes facing away from the radar. This requires slope-adaptive filtering as common-band filters using a fixed wavenumber shift (corresponding to flat terrain) do not provide satisfying results. Fixed-shift filters even lead to increased coherence loss for slopes facing away from the radar. In order to obtain the highest coherence, several slope adaptive common-band filtering methods have been proposed [3, 4, 5]. However, most filters require auxiliary information such as system parameters or topographic information.
Here, we propose a simple slope adaptive common-band filter which is completely data driven. The proposed filter does not require additional information like signal bandwidth, pixel spacing or orbit information. Instead, the signal bandwidth and the corresponding range spectral weighting functions are directly estimated from the single-look complex (SLC) data. The wavenumber shift (in units of array-indices) is locally estimated from the interferogram formed by two SLC images. Nevertheless, for strongly decorrelated interferograms a synthetic interferogram based on an external DEM can optionally be used to improve the wavenumber shift estimation. The proposed common-band filter operates in the frequency domain on small image patches. Therefore it does not require resampling which could deteriorate the coherence. The filter was applied on TanDEM-X scenes over the Swiss Alps and over the Wallerfing test site in Germany as well as on airborne F-SAR acquisitions from the ARCTIC-15 campaign in Greenland. The developed filter shows a significant coherence improvement compared to fixed-shift or fixed-bandwidth filters [3]. Compared to the current state-of-the-art, the topography adaptive filter proposed in [4] which requires two resampling steps, we achieved slightly better results.
The aim of common-band filters is to remove uncorrelated spectral parts in the range spectra of two SLC scenes which lead to decorrelation in the corresponding interferogram [1]. The bandwidth of the uncorrelated spectral parts is determined by the wavenumber shift which is proportional to the local fringe frequency in an unflattened interferogram [2], i.e. an interferogram where the topographic phase is still superimposed by the flat-earth phase.
For the implementation of the slope-adaptive common-band filter, we first estimate the global spectral weighting function (usually a Hamming window) from the range spectrum of two SLC images which form an interferometric pair. The global spectrum contains information about the oversampling factor of the data, and thus the excess-bandwidth, which needs to be considered when the bandwidth of a common-band filter is calculated. To adapt the wavenumber shift to local topography, the coregistered pair is split into overlapping blocks. The block size is determined by a trade-off between estimation accuracy for the wavenumber shift and the patch size over which the filter assumes a constant fringe frequency. In order to minimize boundary effects and to provide smooth transitions between the blocks, the blocks are spatially weighted by a Gabor window. For each block pair the wavenumber shift is calculated from the fringe frequency of the corresponding interferogram. The wavenumber shift is given in units of array indices. Thereby, the algorithm acts only in pixel coordinates and no information about system frequency or pixel spacing is required. In order to apply the wavenumber shift to each block pair, first the global spectral weighting function is removed such that an unweighted range-spectrum is obtained. Then, two identical spectral weighting function of reduced bandwidth are computed for each block pair by scaling the global spectral weighting function to the remaining bandwidth. Then, the new spectral weighting functions are shifted against each other by the local wavenumber shift. Finally, the shifted weighting functions are multiplied with the unweighted range spectrum of the two corresponding blocks. Note, that only the spectral weights are redistributed and that the range spectra themselves are not shifted. After redistribution of the local range spectra, the overall backscatter power in the blocks is scaled to conserve the original backscatter intensities. Blocks for which no fringe frequency could be determined are filtered by an interpolated wavenumber shift obtained from neighboring blocks. For reconstruction of the original SLC scenes, we perform a weighted average of the filtered SLC data contained in the blocks.
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References:
[1] Zebker, H.A. and Villasenor, J. “Decorrelation in interferometric radar echoes”, IEEE Transactions on Geoscience and Remote Sensing, 1992, 30, 950-959
[2] Gatelli, et al. “The wavenumber shift in SAR interferometry”, IEEE Transactions on Geoscience and Remote Sensing, 1994, 32, 855-865
[3] Bamler, R. & Davidson, G. W. “Multiresolution signal representation for phase unwrapping and interferometric SAR processing”, Geoscience and Remote Sensing, 1997. IGARSS '97 Proceedings, 1997, 2, 865-868 vol.2
[4] Reigber, A. “Range dependent spectral filtering to minimize the baseline decorrelation in airborne SAR interferometry”, Geoscience and Remote Sensing Symposium, 1999. IGARSS '99 Proceedings, 1999, 3, 1721 -1723 vol.3
[5] Santoro, M. et al. “Improvement of interferometric SAR coherence estimates by slope-adaptive range common-band filtering.”, IGARSS ‘07 Proceedings, 2007, 129-132
[Authors] [ Overview programme] [ Keywords]
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Paper 356 - Session title: Poster Session 1
Tuesday-73 - Fusion Of Sentinel-1A And Sentinel-1B Data To Discover Of Crop Planting And Crop Phenology Phases
Kussul, Nataliia (1); Shelestov, Andrii (2); Lavreniuk, Mykola (2); Novikov, Alexei (2); Yailymov, Bohdan (1) 1: Space Research Institute, Ukraine; 2: National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”
Show abstract
The European Copernicus program makes acquisitions from the Sentinel-1A (S1A) SAR satellite (launched in April 2014) available under a “full, free and open” data license. S1A acquires with a 12 day revisit frequency over a 185 km swath, a nominal resolution of 10 m (in the default Interferometric Wide mode) and either in single (VV or HH) or dual polarization (VV/VH or HH/HV).
Since 2015 dual polarization (VV/VH) Sentinel-1A coverage of Ukraine with a 12 day repeat frequency (descending mode) is available for the crop growth season. The weather-independent synthetic-aperture radar (SAR) images provided by Sentinel-1A constitute a series of more than 15 images over the Kyiv oblast in 2015 and 2016, which is one of the JECAM test sites. That is much more data than optical data from Landsat-8, for which only 4 images with permissible level of clouds coverage during the same period of time (March - August) in 2015 were acquired, and 4 Landsat-8 images acquires for 2016. In our previous studies we have investigated method for crop classification map derivation based on ensemble of neural networks [1, 2]. It had been explored that crop classification map based on time-series of Sentinel-1A is more accurate than using optical data from Lansat-8 and Spot-5 [3]. We explain the results with the higher temporal resolution of Sentinel-1A data which can be consistently acquired due to cloud independence and the complementarity of the optical and SAR signal response from the crop types.
With launching second SAR satellite Sentinel-1B it will be possible to obtain data more frequently. Consequently, we could calculate coherence between the closest dates from Sentinel-1A and Sentinel-1B to find sudden changes. This approach allows precisely identify when the crop was planted and also specify the date of different crop phenology phases. Those factors are extremely important in soil moisture evaluation, drought indicators assessment and for improving accuracy of crop classification maps.
Detailed experimental results for Sentinel-1A and Sentinel-1B will be presented.
Keywords: agriculture, image processing, data fusion, Sentinel-1A, Sentinel-1B.
[1] N. Kussul, S. Skakun, A. Shelestov, M. Lavreniuk, B. Yailymov, and O. Kussul, “Regional Scale Crop Mapping Using Multi-Temporal Satellite Imagery,” Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci., XL-7/W3, pp. 45–52, 2015.
[2] S. Skakun, N. Kussul, A. Y. Shelestov, M. Lavreniuk, O. Kussul, “Efficiency Assessment of Multitemporal C-Band Radarsat-2 Intensity and Landsat-8 Surface Reflectance Satellite Imagery for Crop Classification in Ukraine,” IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2015, DOI: 10.1109/JSTARS.2015.2454297.
[3] M. Lavreniuk, G. Lemoine, and N. Kussul, “Crop classification strategies using hybrid Sentinel-1, Sentinel-2 and Landsat-8 data series in Ukraine,” European Space Agency Living Planet Symposium, 2016.
[Authors] [ Overview programme] [ Keywords]
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Paper 365 - Session title: Poster Session 1
Tuesday-110 - Monitoring Of Moraine And Glacier Movements In The Chamonix Valley (France) By Means Of Sentinel 1 A/B Interferometry
Jauvin, Matthias (1); Yan, Yajing (1); Trouvé, Emmanuel (1); Fruneau, Bénédicte (2); Col, Fabrice (3); Demeule, Vincent (4) 1: LISTIC, Université Savoie Mont-Blanc, France; 2: Université Paris-Est Marne-la-Vallée Equipe MATIS - IGN; 3: Gascogne Genie Civil, France; 4: MIRE sas, France
Show abstract
The alpine mountain is affected by complex geomorphological processes which lead to slope instabilities that are likely to generate risks for the mountain territories. One of these instabilities corresponds to the evolution of moraines, linked to the glacial conditioning and local geomorphological factors. Moraines can be affected by both large scale deformations over very long time period and localized small scale displacements. In this work, a series of Sentinel-1 images (28 pairs already processed, around 40 expected) are used to investigate the potential instabilities of moraine of the Argentière glacier in the Chamonix valley. Both classical interferometry and Permanent Scatterer interferometry techniques are applied in order to measure the displacement over the moraine and its surrounding slopes. Complementary to these techniques, artificial corner reflectors have been installed and GPS measurements have also been performed in this area. All these measurements are combined together in order to better understand the phenomenon of moraine and further the evolution of the environment of the Argentière glacier.
In the framework of the Copernicus Mission, the European Space Agency has launched a new generation of satellites, started with Sentinel 1A in April 2014. Since September 2016, Sentinel 1B has provided data which allow for acquisitions every 6 days over Europe. The particular acquisition mode of Sentinel images requires a very precise co-registration between interferometric pairs, especially in azimuth, which makes the interferometric processing of Sentinel-1 images challenging. However, the short revisit time, the precise orbital data and the small perpendicular baselines from one acquisition to another, provide prospects for improving the precision of displacement measurement. Moreover, Sentinel 1 data are free, which guarantees the continuous availability of data for all applications. For all these reasons, the arrival of Sentinel-1 A and B data offers good opportunity to develop operational monitoring applications for instabilities and displacements measurements in mountain area.
Moreover, with 6-day interferograms built with S1-A/S1-B pairs, the temporal decorrelation is reduced. On such pairs, we can expect the coherence to be sufficient to observe fringes patterns on the glacier surface. On Chamonix-Mont-Blanc glaciers (low latitude, altitude of 2000 to 4800m), this is possible only during the cold season and with favorable anti-cyclonic meteorological conditions. Since the launch of Sentinel 1-B, few months ago, only one pair (4-10 October) shows sufficient coherence and fringes patterns similar to those observed with ERS (1 day interferograms) in 1995-1996. During the coming winter, we expect to have more 6-day interferograms with sufficient coherence on glacier surface. In this case, our first results on a combined analysis of moraine instabilities and glacier displacements will be presented at Fringe 2017.
[Authors] [ Overview programme] [ Keywords]
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Paper 366 - Session title: Poster Session 1
Tuesday-140 - Updating a DInSAR time series using a modified SBAS algorithm with an incremental SVD: Preliminary results
de Ruyt, Rayner (1); Euillades, Pablo Andres (1); Euillades, Leonardo Daniel (1); Caselli, Alberto (2) 1: FI - UNCuyo & CONICET, Argentine Republic; 2: LESVA - U. Nac. de Rio Negro & CONICET, Argentine Republic
Show abstract
One limitation of the algorithms for computing DInSAR time series is that all available data must be processed at once. So, in order to update the time series the whole dataset must be reprocessed when new scenes arrive. Considering the growing number of available acquisitions and the shortening of revisit time between them, this affects the potential of this type of techniques to be transformed into semi-real time monitoring systems[1]. One of the most used algorithms for computing deformation time-series is Small Baseline Subset (SBAS). It estimates the temporal evolution of surface displacement based on SAR images pairs characterized by low temporal and geometric baselines [2]. The algorithm’s core is to invert the relative displacement between SAR scenes using a minimum norm criteria, and implemented via the Singular Value Decomposition (SVD).
In this contribution we propose a modification to the SBAS algorithm which allows recursively adding new scenes to an already computed time-series. Given a time-series obtained from a number of already acquired scenes via the SVD-based inversion, including and additional acquisition is performed with the following steps: 1) computing new differential interferograms between the new scene and a number of old ones, taking care of not exceed the temporal and geometric baseline limitations, 2) update the coherence masks by considering the new interferograms, 3) independently unwrap the new interferograms by using the updated coherence mask [3] and 4) re-compute the time-series by using a modification low-rank algorithm for a thin SVD [4]
The last step consist in updating the thin SVD of the incidence-like matrix generated in the original processing. In particular, we modify its eigenvalues, and subsequently their respective left and right singular vectors, through the virtual insertion of rows (interferograms) and columns (SAR images) in the aforementioned matrix. This way we are able of updating the equation system solution without re-computing the whole inversion.
We applied the proposed algorithm to 114 COSMO-Skymed stripmap scenes acquired between June 2011 and July 2013 at the Caviahue Copahue Volcanic Complex (border between Argentina and Chile). The CCVC has suffered recent eruptive activity, showing an inflation process of approximately 7 cm/year centered in the northern flank of the Copahue Volcano [5]. Temporal and perpendicular baseline constrains are 365 days and 600 meters, respectively. ASTER GDEM was employed for topographic phase compensation. Phase unwrapping was performed using the Minimum Cost Flow algorithm.
Firstly, we computed a time series via SBAS processing of the whole dataset, in order to generate a known result. Then, we constructed a partial solution by using the first 52 scenes and subsequently increased the number of scenes by executing steps 1 to 4 mentioned previously. Preliminary comparative results indicate that the time-series obtained by updating the solution shows high correlation with the control results. The comparison was performed over pixels present at the updated coherence mask, within and outside the deformation area.
Future development will focus in testing different case studies, particularly a synthetic one, and incorporating algorithms which allow increasing the optimization and numeric stability of the results.
References
[1] P. S. Marinkovic, F. van Leijen, G. Ketelaar, and R. F. Hanssen, “Recursive data processing and data volume minimization for PS-InSAR,” in Proceedings. 2005 IEEE International Geoscience and Remote Sensing Symposium, 2005. IGARSS ’05., 2005, vol. 4, pp. 2697–2700.
[2] P. Berardino, G. Fornaro, R. Lanari, and E. Sansosti, “A new algorithm for surface deformation monitoring based on small baseline differential SAR interferograms,” IEEE Trans. Geosci. Remote Sens., vol. 40, no. 11, pp. 2375–2383, Nov. 2002.
[3] M. Costantini, “A novel phase unwrapping method based on network programming,” IEEE Trans. Geosci. Remote Sens., vol. 36, no. 3, pp. 813–821, May 1998.
[4] M. Brand, “Fast low-rank modifications of the thin singular value decomposition,” Linear Algebra Its Appl., vol. 415, no. 1, pp. 20–30, May 2006.
[5] Copahue Volcano, F. Tassi, O. Vaselli, A.T. Caselli, Editors, Active Volcanoes of the World Series, Ed. Springer-Verlag, Berlin Heidelberg, 2016
[Authors] [ Overview programme] [ Keywords]
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Paper 368 - Session title: Poster Session 1
Tuesday-85 - First Results Of Ground Displacement Monitoring In Paris (France) With Sentinel 1 A/B Time Series
Jauvin, Matthias (1); Yan, Yajing (1); Fruneau, Bénédicte (2); Trouvé, Emmanuel (1); Gusmano, Pierre (3) 1: LISTIC, Université Savoie Mont-Blanc, France; 2: Université Paris-Est Marne-la-Vallée, Equipe MATIS - IGN, France; 3: MIRE sas, France
Show abstract
SAR differential interferometry represents an efficient tool to spatially monitor small ground deformations. During the last fifteen years, methods based on image time series, such as Persistent Scatterers technique, have shown their capabilities for monitoring finer displacements with millimeter precision. With the launch of Sentinel 1A and 1B in April 2014 and 2016, it is now possible to work with free time series of medium resolution images. The rapid revisit time (6 days) of this new constellation limits the temporal decorrelation, which makes it possible to have a high PS density, especially in urban areas. This reduction of the distance between PSs would then reduce the dispersion of the displacement measurements, so that the main source of error in deformation measurement will be due to the variation of the atmospheric composition.
Major cities such as the city of Paris are experiencing constant changes that involve major construction works, both on the surface and underground. Paris for instance has started a new project called “Grand Paris”, which aims at transforming the Parisian metropolitan area with in particular major developments in transport network (subway, train and tramway). Such projects usually come with important pumping of groundwater or large excavations, whose surface impacts must be monitored with precision during and after the operations. In this context, Sentinel 1 data is a promising alternative of precedent radar satellite images, which guarantees the continuous availability of data for all applications and offers a good opportunity to develop operational monitoring applications. Even with a medium resolution, it is still possible to consider a use of this technique for monitoring displacements related to human activity (pumping of groundwater, construction of underground structures…) in urban areas.
In this paper, we will present our first results obtained with a stack of Sentinel 1A and 1B images (29 images from S1-A and S1-B already processed, probably 45 for the Fringe workshop) acquired in IW mode. The PS processing is performed by using Gamma software. Some specific areas where construction works have already started are currently investigated to try to identify meaningful displacement patterns. In order to avoid limitations such as difficult PS identification and wrong interpretation of the deformation, we consider integrating PS results in processes of monitoring with others geodetic measurements (GPS, tachometry or leveling) acquired by companies specialized in high-precision topography, in order to better analyze and understand the deformations, their related processes and risks.
[Authors] [ Overview programme] [ Keywords]
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Paper 370 - Session title: Poster Session 1
Tuesday-93 - Quantitative analysis of PS displacement and positioning accuracy exploiting co-polarized and cross-polarized Sentinel-1A/B interferometric wide-swath data
Costantini, Mario (1); Minati, Federico (1); Vecchioli, Francesco (1); Prats-Iraola, Pau (2); Nannini, Matteo (2); Yague-Martinez, Nestor (2) 1: e-GEOS - an Italian Space Agency and Telespazio company, Italy; 2: DLR Microwaves and Radar Institute, Germany
Show abstract
Several experiments have proved the effectiveness of the ESA Sentinel-1 A and B (S1A and S1B) satellites for ground deformation monitoring, in particular thanks to the capability of performing frequent acquisitions of very large areas in the interferometric wide-swath TOPS mode. When properly processed, the S1 TOPS data guarantee also very accurate ground deformation measurements.
In this work, we focus on an aspect not fully studied yet, i.e. accuracy of the S1 interferometric measurements on real targets, in particular persistent scatterers (PS), intended in the general sense of scatterers that exhibit interferometric coherence for the time period and baseline span of the acquisitions, including both point-like and distributed scatterers.
We quantitatively analyze the accuracy of the PS deformation measurements obtained with S1A and S1B TOPS data. We also quantitatively characterize the achievable 3D positioning accuracy of the deformation measurements (positioning of the PS points), which depends not only on the interferometric phase noise but also on the baseline values. A theoretical analysis and several experiments on real cases showing the S1 capabilities in terms of deformation and 3D positioning accuracy will be reported.
In particular, the availability of both co-polarized and cross-polarized S1 data are exploited to obtain a precise estimation of the phase noise level and of the PS deformation and 3D positioning accuracy. In fact, co-polarized and cross-polarized S1 acquisitions are contemporary. Therefore, the common (visible on both channels) PS are characterized by the same phase contributions, i.e. topographic, atmospheric, target backscattering and possible displacement (except possibly for the fact that the dominant contribution to the pixel could come from slightly different positions in the two channels). Therefore, the phase noise characterizing the common PS measurements can be isolated from atmospheric artifacts.
The obtained results confirm the interferometric capabilities of S1 and made possible to quantitatively characterize its interferometric measurements accuracy performance on real targets.
Other interesting effects are visible from the performed analysis, like a miscalibration between the VV and VH channels removed with the antenna pattern correction introduced in the ESA focusing processor.
In addition, the performed analyses made possible to determine the practical effect of even small misregistration effects on phase noise, which can suggest to perform a more sophisticated coregistration approach involving all possible interferometric pairs.
[Authors] [ Overview programme] [ Keywords]
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Paper 371 - Session title: Poster Session 1
Tuesday-72 - Two Years of Sentinel-1 Observations Over Austria
Gutjahr, Karlheinz (1); Leopold, Philip (2) 1: Joanneum Research, Austria; 2: AIT Austrian Institute of Technology GmbH, Austria
Show abstract
Within the research project “Sentinel-1 InSAR”, funded by the Austrian Research Promotion Agency, single look complex (SLC) data was systematically gathered over Austria since the launch of Sentinel-1A and later Sentinel-1B. Main objectives of the projects were on necessary methodological development issues raised by the novel TOPS acquisition used in the Sentinel-1´s interferometric wide swath mode. On the other hand, the applicability of the Sentinel-1 data to observe surface changes over the various landscapes of Austria should be investigated.
In the paper adaptions to basic interferometric processing steps like coregistration, de- and reramping are presented as well as new tasks like debursting and burst merging. Especially the phase preserving burst merging turned out to be a challenging topic over alpine areas due to temporal decorrelation effects. However, the 6 day repeat cycle between Sentinel-1A und 1B could relax these problems to certain extend.
The well-known small baseline subset (SBAS) technique was used to analyse the compiled data stacks. To deal with the aforementioned alpine terrain but also with large forest areas, or generally speaking vegetated terrain without persistent scatter like objects, the EMCF phase unwrapping was incorporated in this workflow . We also included some recent developments like a multi-temporal phase filter and the search for the optimal interferogram selection into the workflow. The efficiency of these further improvements was quantified by numerical simulations and analysis of the gain in coherence and model consistency.
Finally for dedicated test sites showing different surface change characteristics, the achieved results were compared to either terrestrial measurements and/or simultaneously acquired TerraSAR-X data stacks in stripmap and staring spotlight mode. For example the surface movements of a giant landslide (surface in motion more than 1 km2) in eastern Autria was monitored in the field during a one year period with high accuracy GPS measurements. The landslide is an active creep movement with documented deformations since 1876, expected surface motions are in the range of cm to mm per year. It is part of the ongoing work in the project to compare these field results with the above mentioned remote sensing data of the same period. As outcome of the project we expect results, if and how Sentinel 1 and other remote sensing data can support or even replace terrestrial measurements and if there are possibilities to establish early warning systems for landslides based on remote sensing radar data.
[Authors] [ Overview programme] [ Keywords]
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Paper 372 - Session title: Poster Session 1
Tuesday-12 - Joint Correction of Atmospheric Effect and Orbital Error
Chen, Xue; Peng, Junhuan; Yang, Honglei China University of Geosciences, China, People's Republic of
Show abstract
The success and accuracy of InSAR in measuring surface deformation are strongly affected by various noise sources, including atmospheric effect, orbital error, residual topography error and decorrelation noises. Atmospheric effect may easily mask surface displacement due to tectonic movement or volcanic activity. Orbital error causes an almost linear signal and scales the height ambiguity. It may be misinterpreted in the presence of a large scale deformation signal like tectonic movement or tides that has similar spatial characteristics. A method jointly correct atmospheric effect and orbital error in multitemporal InSAR is proposed. A nonlinear least square approach based on variance-covariance estimation is applied to improving the orbital accuracy. A GPS Topograph-dependent Turbulence Model is chosen to reduce the atmospheric effect with ground control points and available GPS measurements. Both simulation experiment and real experiment show that, atmospheric effect and orbital error signal distribution are effectively mitigated. Atmospheric effect is almost eliminated. The InSAR measurement accuracy is improved by the proposed joint correction method. Results demonstrate that the proposed joint correction technique provides a promising way to jointly correct atmospheric effect and orbital error.
[Authors] [ Overview programme] [ Keywords]
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Paper 384 - Session title: Poster Session 1
Tuesday-151 - Estimation of Displacements from Italy's 30.10.2016 Earthquake Using 3-Pass Differential Interferometry
Danisor, Cosmin (1); Dana Negula, Iulia (2); Datcu, Mihai (3) 1: University Politehnica of Bucharest, Romania; 2: Romanian Space Agency; 3: German Aerospace Center
Show abstract
Objectives
Developing and implementing a differential interferometric processing chain to estimate the displacements caused by 30.10.2016 earthquake in Perugia region, Italy. The 3-pass differential interferometry was preferred because of the possibility to generate a digital elevation model with the same resolution of SAR images. Furthermore, because the same reference image is used to estimate the topographic term of interferometric phase and to generate the differential interferogram, this method does not require the coregistration of the estimated topographic component with the interferogram of the differential pair of images. The proposed processing chain is applied on images acquired by Sentinel-1 mission (both 1A and 1B satellites) in TOPS (Terrain Observation in Progressive Scans) mode, with pixel spacing of 2.32 m in range direction and 13.94 m in azimuth. The steps of the processing chain will be implementing using the interferometric and differential interferometric functionalities of Gamma Remote Sensing processor.
SAR Images Dataset Selection
The images’ dataset consists of three acquisitions, from which two are used to estimate the topographic component of interferometric phase (topographic pair) and two are used to derive the differential interferogram (differential pair). Both pairs have the same reference image. Both images of topographic pair are acquired before the earthquake, and have a small temporal baseline Δt (to minimize the effects of temporal decorrelation) and a large perpendicular baseline bp (to increase the topographic phase’s sensitivity to terrain’s height). The differential pair consists of one image acquired before and one image acquired after the occurrence of natural disaster. The perpendicular baseline of this pair ideally must be lower, to increase the interferometric phase’s sensitivity with displacement’s component.
Images Pre-Processing
Each image consists of 3 swaths, composed form 9 distinct bursts each. The image of the whole scene is formed by concatenating its distinct portions, operation named de-bursting. Because each image it’s acquired from a different position, slave images need to be resampled in the geometry of master acquisition. This coregistration step needs to be implemented on the whole scene, with high accuracy, otherwise the Doppler shifts between consecutive bursts will affect the next interferometric processing steps. Initial offsets between each master-slave pair are estimated from satellite’s orbital information. The offsets are then upgraded by maximization of amplitude’s correlation coefficient, in windows defined across the scene. Non-linear offsets are estimated by generation of interpolation polynomials.
Estimation of Topographic Component
For computational reasons, the following processing steps were applied exclusively on the scene’s portion containing the epicenter of earthquake. Interferogram generation was accompanied by filtering of spectrum’s common band only in range direction, the azimuth spectrum being affected by Doppler frequency shifts. To facilitate the phase unwrapping step, interferogram flattening was carried. Contribution of earth’s surface curvature was estimated from information related to satellite’s orbit trajectories. This contribution will be re-added before the generation of differential interferogram. Interferometric phase filtering is carried to attenuate system’s noise component and to compensate the effects of non-uniform propagation of waves through atmosphere. Adaptive filtering is implemented, by using a filter adapted to interferogram’s power spectral density. In this step, spatial distribution of amplitude’s coherence is also estimated. Phase unwrapping is carried with minimum cost flow algorithm, using Delaunay triangulation. Regions with amplitude’s coherence below 0.3 are initially excluded from processing. Unwrapped phase of those areas will be estimated using interpolation
Differential Interfeogram Computation. Displacements estimation
The processing steps implemented for generation of topographic component are applied for estimation of unwrapped interferometric phase of differential pair of images. From newly obtained interferogram, the estimated topographic phase must be subtracted, so deformation component of interferometric phase will become dominant. Earth’s curvature component will be re-added to inteferograms of both image pairs. Considering that the two pairs have different perpendicular baselines, estimated topographic component must be adapted to differential pair interferogram before subtraction.
Future Work
Future steps include geo-referencing the obtained deformation map and a method for validation of the results. Refinement of the results will also be considered
[Authors] [ Overview programme] [ Keywords]
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Paper 385 - Session title: Poster Session 1
Tuesday-64 - Exploitation of Sentinel-1 Interferometric Coherence for Land Cover and Vegetation MAPPING (SInCohMap Project)
Jacob, Alexander (1); Notarnicola, Claudia (1); Duro, Javier (2); Engdahl, Marcus (3) 1: EURAC Research, Italy; 2: DARES Technology, Spain; 3: European Space Agency
Show abstract
In this abstract a new ESA SEOM project is presented, which will start in January 2017.
The main objective of this research is to develop, analyze and validate novel methodologies for land cover and vegetation mapping using time series of Sentinel-1 data and in particular by exploiting the temporal evolution of the interferometric coherence. Further the project aims on quantifying the impact and possible benefit of using Sentinel-1 InSAR (Interferometric Synthetic Aperture Radar) data relative to traditional land cover and vegetation mapping using optical data (especially Sentinel-2) and traditional intensity-based SAR (Synthetic Aperture Radar) approaches.
The main classes sought after are Forests, Agricultural areas (e.g. Crops), Artificial surfaces (e.g. Urban), Water Bodies, Scrub and Herbaceous Vegetation, Open or bare land with little to no vegetation and Wetlands.
We have setup three different reference test areas with very accurate ground truth data for performing quantitative assessment and validation in Spain, Italy and Poland.
In order to scientifically evaluate the performance of different methodologies for land cover and vegetation mapping a round robin is organized. Participants will get access to pre-processed datasets over the three study areas together with some access for relevant training data for classification purposes. Further participants will also get access to processing facilities via a private cloud platform hosted at EURAC Research. The kickoff for this round robin will be in April 2017 and it will stay active for 4-6 month. Finally, we will organize a workshop where the main results will be presented by the participant teams together with a round table to analyze the results and set the conclusions.
Besides presenting this new project, the aim of this poster is to present and disseminate this initiative and to foster the participation of the InSAR community present at Fringe and interested in those topics.
[Authors] [ Overview programme] [ Keywords]
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Paper 388 - Session title: Poster Session 1
Tuesday-5 - The Effect of Temporal Resolution Due to Atmospheric Phase Delay on Minimum Detectable Signal in InSAR Time Series: Application to Slow Deformation over Socorro Magma Body
Havazli, Emre (1); Wdowinski, Shimon (2) 1: University of Miami, United States of America; 2: Florida International University, United States of America
Show abstract
InSAR time series techniques are very useful tools for detecting and monitoring crustal movements induced by tectonic and non-tectonic processes, as earthquakes, magmatism, and land subsidence. The products of time series analyses, velocity maps, provide spatially detailed information on the deformation process, but are also affected by various noise sources, including atmospheric phase delay and decorrelation. Reducing measurement uncertainties require the use of long time series. However, it is not clear how long and how many acquisitions are needed for achieving a detection threshold.
In this study, we evaluate the contribution atmospheric phase delay to the measurement uncertainties on InSAR time series products. We quantify velocity uncertainty levels with respect to the time series temporal resolution (acquisition interval, time series length, and data gaps). Our study relies on simulations of a deformation signal along with atmospheric phase delay, which includes both stratified and turbulent atmospheric phase delay components. We chose our deformation signal as a Mogi source with an uplift rate of 2 mm/yr (Mogi K., 1958). Atmospheric noise sources are characterized by using methods proposed in previous studies (Hanssen, 1998; Gonzalez and Fernandez, 2011; Agram and Simmons, 2015) and a real digital elevation model (DEM) in the case of the stratified phase delay. The incremental deformation signal and the atmospheric phase delay are calculated for each simulated acquisition, which are later combined to generate interferograms. The core of our study includes time series analysis of simulated data using the PySAR algorithm, which is the University of Miami version of the Small Baseline Subset (SBAS) method, and statistical analysis comparing time series results with different time series lengths, number of acquisitions, and various randomly generated atmospheric noise scenarios.
We applied our simulation tool to the slow deformation of Socorro Magma Body (SMB) in New Mexico, USA, which has uplifted at a slow rate of 2 mm/yr (Fialko and Simmons, 2001; Finnegan and Pritchard, 2009; Pearse and Fialko, 2010). We simulated C band phase data corresponding to the available ERS and Envisat datasets acquired during the years 1992-2006, and 2006-2011, respectively. Our results indicate that, in the case of solely stratified atmospheric phase noise presence, 5 years is critical for reaching uncertainty level of 1 mm/yr with 95% confidence limit. After 5 years, the improvement of velocity uncertainty diminishes gradually. Our simulation results are in agreement with ERS and Envisat data analysis results indicating that the 15-year long ERS dataset can detect the slow uplift, whereas the 4.5-year long Envisat dataset produced very noisy results.
[Authors] [ Overview programme] [ Keywords]
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Paper 389 - Session title: Poster Session 1
Tuesday-137 - The Impact of Temporal and Geometrical Phase Decorrelations on the Uncertainty Level of InSAR Time Series Estimations
Havazli, Emre (1); Wdowinski, Shimon (2) 1: University of Miami, United States of America; 2: Florida International University, United States of America
Show abstract
InSAR time series analysis is an important tool for studying deformation of the Earth’s surface. One of the major limitations of InSAR is decorrelation due to temporal surface processes and acquisition geometry, which are characterized by temporal and perpendicular baselines, respectively. Decorrelation results degraded interferometric coherence in individual interferograms, which propagates into errors in InSAR time series products. Although the decorrelation effect is a major error source in InSAR time series analyses, it hasn’t been studied widely.
In this study, we aim at quantifying the decorrelation effect on InSAR time series results using simulated data. Our initial study is based on simulated C band data carrying the characteristics of ERS and Envisat satellites without atmospheric phase delay. We first generate an acquisition network with typical temporal and geometrical baselines, ranging between 35-800 days and 0-500 meters, respectively. We then, generate interferograms based on a Delaunay triangulation method and apply the decorrelation effect as spatial white noise that is added to phase in an interferogram. The amplitude of the white noise is calculated differently for geometrical and temporal cases. For geometrical decorrelation, the amplitude is calculated linearly, inversely proportional to the baseline normalized to the satellite critical baseline. Geometrical decorrelation is highest when the perpendicular baseline is equal or higher than the critical baseline and decreases linearly with lower baseline length. Temporal decorrelation is a more complicated issue as it is not just affected by the time difference between two acquisitions but also affected by surface type (arid, vegetated, urban etc.) of the area of interest. In our preliminary study, we use a single surface type and assume that the decorrelation level, which is modeled as the amplitude of the spatial white noise, increases logarithmically (or exponentially) with time. The characteristic logarithmic increase time vary based on surface type. After generating the synthetic interferograms, we use the PySAR algorithm, which is the University of Miami version of the Small Baseline Subset (SBAS) method, to carry on time series analysis of our data. Our initial results indicate increasing unwrapping errors with increased decorrelation effects, which significantly degrade the outcome of the time series analysis results. Future work will quantify the uncertainty level resulting from geometrical decorrelations, temporal decorrelation and their combined effect.
[Authors] [ Overview programme] [ Keywords]
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Paper 390 - Session title: Poster Session 1
Tuesday-132 - Joint Estimation of Distributed Scatterer Target Statistics for Improved Phase-Linking of Multiple InSAR Stacks
Eppler, Jayson; Rabus, Bernhard Simon Fraser University, Canada
Show abstract
A posteriori fusion of InSAR derived multi-temporal deformation estimates from two or more line-of-sight geometries is frequently employed as a means to estimate two-dimensional deformation quantities or to increase the effective temporal sampling rate. However, such a fusion of independently derived estimates does not consider the possibility that target parameters such as the spatial extent and the complex coherence of distributed scatterers (DS) may exhibit significant correlations between different incidence angles and even between opposing sensor look directions. Higher accuracy and improved robustness compared to the usual a posteriori fusion scheme can be achieved by exploiting these correlations with true multi-stack InSAR processing (a priori fusion).
In this work, we demonstrate increased performance through multi-stack generalization for existing phase-linking methods that utilize the estimated coherence of DS defined over local spatial regions of homogeneous statistics. These methods involve three steps: the first identifies local homogeneous regions to analyze as DS, the second estimates the target complex coherence over these regions and the third exploits the coherence estimates to project the network of partially redundant interferometric phases to a subspace representing fully redundant phases. The energy of the phase residuals which result from comparing the redundant and non-redundant phases then serves as a measure of DS quality which may also be exploited during subsequent processing.
For the multi-stack generalization, from these steps we identify the DS spatial extents, complex coherence and target quality measure as DS characteristics that can be modelled so that a parametric subspace invariant to sensor look direction can be constructed. We present a method for jointly estimating these DS characteristics and their use for simultaneous phase linking and DS quality assessment of the multiple InSAR stacks.
Results are presented and compared for simulated DS as observed from multiple look directions and for real RADARSAT-2 Spotlight mode data stacks for two locations: a pair of ascending and descending pass direction data stacks over the city of Seattle Washington representing an urban case and also a pair of same-side stacks over the village of Umiujaq in northern Canada representing a permafrost monitoring case.
[Authors] [ Overview programme] [ Keywords]
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Paper 391 - Session title: Poster Session 1
Tuesday-34 - Present-day Deformation in Taiwan Mountain Belt as Monitored by InSAR
Fruneau, Benedicte (1); Pathier, Erwan (2); Doin, Marie-Pierre (2); Hu, Jyr-Chin (3); Tung, Hsin (4) 1: Universite Paris-Est Marne-la-Vallee, France; 2: Universite Grenoble Alpes, France; 3: National Taiwan University, Taiwan; 4: Academia Sinica, Taiwan
Show abstract
Taiwan Island, resulting from oblique collision between Philippine sea plate and Eurasian plate converging at a rate of about 8 cm per year, is one of the most active tectonic region in the world. With a subtropical environment, it is faced to different hazards, including earthquakes, debris flow, landslides, and flooding. The precise measurement of the present-day ground displacements at the scale of the whole Taiwan Island is thus essential in several domains of Earth Sciences, in particular for earthquake cycle study and earthquake hazard assessment, for subsidence and landslide monitoring, and also to better understand the kinematics and mechanics of mountain building.
In the framework of our complete mapping of Taiwan Island with InSAR, we use in this study the full archive of SAR data acquired by ALOS-1 satellite on the 2007-2011 period. ALOS L-band data are very effective in the vegetated and hilly Taiwan environment. SAR images are processed through a small baseline approach with NSBAS interferometric chain (Doin et al., 2015). It includes several corrections applied before unwrapping, in particular correction of atmospheric delays predicted from the global atmospheric re-analysis ERA-Interim model, and local DEM error correction. These corrections are of particular importance as they reduce the variance of the phase across regions with high topographic gradients, hence preventing unwrapping errors. Unwrapping process is also performed using a specific scheme, taking into account the information of colinearity.
Thanks to this careful processing, we are able to unwrap across the Central Range, a challenging area with more than 3000m of topographic ranges. InSAR offers an unprecedented continuous view of deformation field of a large part of the Central Range. LOS velocity map obtained on track 446 shows a clear pattern of deformation, consistent with a rapid uplift of the Central Range South of the island. This uplift, already partially documented by GPS and leveling, is clearly mapped here and seems to show overall continuity. However, details of this map should be analyzed with caution.
This is a real contribution of InSAR with respect to GPS, with a dramatic increase of the spatial information: even if the density of GPS stations is high in Taiwan, they are mostly distributed around the Central Range, and do not offer such spatial sampling.
On this track, InSAR results allow also to connect spatially south western part of Taiwan, mapping the deformations of the Foothills and the Coastal Plain, and the southern end of the Longitudinal Valley, showing aseismic creep.
[Authors] [ Overview programme] [ Keywords]
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Paper 392 - Session title: Poster Session 1
Tuesday-119 - Adaptive Filter Kernel Selection for Phase-linking Performance Optimization
Eppler, Jayson; Rabus, Bernhard Simon Fraser University, Canada
Show abstract
Adaptive filtering in InSAR stack processing compares neighbouring resolution cells to identify spatially contiguous homogeneous regions of scatterers; it is often used as a precursor step to phase-linking or target decomposition steps. There are conflicting demands on the size of these regions expressed as their number of looks: a fixed lower bound for the number of looks ensures that the estimated target coherence is well conditioned and that sufficient phase noise suppression is achieved. On the other hand, compact kernels with just a few looks can be desirable because they result in higher spatial resolution and reduce likelihood of spatial aliasing during coherence estimation. Consequently, a good compromise goal of adaptive kernel formation is to achieve some desired number of spatial looks while maximizing spatial compactness and minimizing inclusion of spatial samples violating homogeneity.
Several methods have been proposed for identifying homogeneous regions based on similarity of amplitude distributions. These include the well know Kolmogorov-Smirnov, Anderson-Darling and Generalized Likelihood Ratio tests. The application of these tests for kernel formation involves their inclusion in a cost function used for pairwise comparison of spatial samples combined with some acceptance threshold. Kernel inclusion of spatial samples may be further constrained, e.g. by requiring spatial connectedness.
For a given kernel inclusion cost function, the selection of the inclusion threshold and additional constraints will have a significant effect on kernel compactness and the degree of homogeneity achieved. In this work we present the first comprehensive study of the impact of inclusion threshold and connectedness constraints and how they affect both kernel compactness and resulting target statistics including linked-phase errors. Our analysis covers a representative set of parameters describing heterogeneity conditions such as target morphology (e.g. edges, point targets) and type of heterogeneity (such as differences in amplitude, coherence model parameters, and phase).
We compare results calculated from simulated data with those obtained for actually encountered heterogeneity conditions in a RADARSAT-2 InSAR stack over Seattle Washington.
[Authors] [ Overview programme] [ Keywords]
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Paper 393 - Session title: Poster Session 1
Tuesday-1 - Application and Performance of Geodetic Corrections for InSAR Processing
Rodriguez Gonzalez, Fernando (1); Parizzi, Alessandro (1); Cong, Xiaoying (2); Gomba, Giorgio (1) 1: German Aerospace Center - DLR, Germany; 2: Technical University of Munich - TUM, Germany
Show abstract
The Sentinel-1 mission provides systematically acquired SAR data for interferometric applications with an unprecedented wide swath. This opens up the possibility of wide area surface deformation monitoring. On such large areas the variation of phenomena such as atmospheric propagation delay and geodynamic effects cannot be neglected. These signals must be as far as possible mitigated in order to provide accurate wide area deformation measurements [1]. Our approach is to exploit the Imaging Geodesy technique for this purpose.
Imaging Geodesy [2] [3] was originally developed in order to allow exploitation the absolute pixel localisation of SAR. It is based on an accurate correction of geodynamic effects as well as tropospheric and ionospheric delays. Validation based on corner reflectors has demonstrated centimetre-level accuracy in both range and azimuth with the TerraSAR-X and TanDEM-X satellites [4]. Based on this well-established technology, the SAR Geodesy Processor (SGP) [5] was developed at DLR. It calculates these corrections based on the following external datasets: numerical weather prediction datasets (NWP) from ECMWF for integrating tropospheric delay, the global TEC map from CODE for calculating ionospheric delay and ephemerides from NASA for modelling Solid Earth Tides (SET) effects.
The first objective of this paper is the description of how the SGP corrections have been introduced into InSAR processing. Two upgrades are required: co-registration and phase simulations. Inherently both are analogous and may be jointly performed in the DEM-based simulations [6] at the core of them or as a-posteriori correction of the standard simulations. Our approach is the latter, i.e. to correct both of the geometrical predictions. The approach has been introduced into DLR’s Integrated Wide Area Processor (IWAP) [7], using the core functionalities from SGP.
Our second objective is to assess the gain performance for co-registration and interferometric applications. It is foreseen to systematically analyse the following aspects:
a) Residual co-registration offsets, which without performing corrections can reach several decimetres in range due to the variation of the absolute tropospheric delay and SET effects. This assessment is of interest in order to support the interpretation of co-registration offsets (and pixel tracking) as motion.
b) Residual phase components, both from the perspective of spatially low pass signals in flat areas, as well as height-correlated signals due to tropospheric stratification. The variograms of the residual phase for different areas will be evaluated on InSAR stacks. The magnitude of these variograms is essential to assess the performance in wide area deformation estimation as a function of distance.
At the moment of this submission our current assessment is qualitative and based on a set of selected sites and for Sentinel-1 and TerraSAR-X (see attached PDF). Further quantitative analysis will be carried out with Sentinel-1 data stacks.
References
[1] Adam, N., Liebhart, W., Parizzi, A., Rodriguez-Gonzalez, F., Brcic, R., “Persistent Scatter Interferometry Wide Area Product Methodology and Final Characteristics,” Terrafirma Stage 3, DLR-IMF – Remote Sensing Technology Institute, 2012.
[2] Eineder, Michael und Minet, Christian und Steigenberger, Peter und Cong, Xiaoying und Fritz, Thomas (2011) Imaging Geodesy—Toward Centimeter-Level Ranging Accuracy With TerraSAR-X. IEEE Transactions on Geoscience and Remote Sensing, Vol. 49 (Issue 2), Seiten 661-671. IEEE.
[3] X. Cong, U. Balss, M. Eineder, and T. Fritz, “Imaging geodesy - centimeter-level ranging accuracy with terrasar-x: An update,” Geoscience and Remote Sensing Letters, IEEE, vol. 9, no. 5, pp. 948–952, Sept 2012.
[4] Balss, U., Gisinger, C., Cong, X. Y., Brcic, R., Hackel, S., & Eineder, M. (2014, June). Precise measurements on the absolute localization accuracy of TerraSAR-X on the base of far-distributed test sites. In EUSAR 2014; 10th European Conference on Synthetic Aperture Radar; Proceedings of (pp. 1-4). VDE.
[5] M. Eineder, U. Balss, S. Suchandt, C. Gisinger, X. Cong and H. Runge, "A definition of next-generation SAR products for geodetic applications," 2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Milan, 2015, pp. 1638-1641.
[6] E. Sansosti, P. Berardino, M. Manunta, F. Serafino and G. Fornaro, "Geometrical SAR image registration," in IEEE Transactions on Geoscience and Remote Sensing, vol. 44, no. 10, pp. 2861-2870, Oct. 2006.
[7] Rodriguez Gonzalez, Fernando und Adam, Nico und Parizzi, Alessandro und Brcic, Ramon (2013) The Integrated Wide Area Processor (IWAP): A Processor For Wide Area Persistent Scatterer Interferometry. In: Proceedings of ESA Living Planet Symposium 2013. ESA Living Planet Symposium 2013, 9–13 September 2013, Edinburgh, UK.
[Authors] [ Overview programme] [ Keywords]
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Paper 395 - Session title: Poster Session 1
Tuesday-35 - An evaluation of methods for the integration of InSAR and GPS data for the derivation of high-resolution surface velocity and strain rate fields
Weiss, Jonathan Randall; Hussain, Ekbal University of Leeds, United Kingdom
Show abstract
Earthquake hazard assessment largely depends on the availability of high resolution and accurate surface velocity and strain rate information for tectonically active regions. The ongoing densification of GPS networks and improvements in our capability to measure deformation using InSAR has enhanced our ability to confidently map regions of localized strain. However, before detailed strain rates can be calculated by taking the spatial derivative of the velocity field, a continuous or dense representation of that field is required. Here we present our progress to date on combining InSAR-derived surface displacements from satellites including Sentinel-1A/B and GPS data to produce large-scale crustal velocity fields and strain models for portions of the Alpine-Himalayan belt. We evaluate “non-physical” approaches that use mathematical functions to interpolate the surface velocities on to regular grids and “physical” methods that ensure elastic coupling between the components of the interpolation. We address methods commonly used to combine the complementary geodetic datasets, incorporation of the associated errors, and the influence of data density and quality on the velocity field inversions. Overarching goals of our effort are to evaluate how strain is distributed across actively deforming regions, identify where seismic hazard (i.e. strain) is focused, assess whether vertical deformation can be resolved, investigate how strain rates vary during the seismic cycle, and compare decadal estimates to those made over longer timescales.
[Authors] [ Overview programme] [ Keywords]
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Paper 398 - Session title: Poster Session 1
Tuesday-65 - Soil moisture mapping using SMAP and Sentinel-1 data
Kuchma, Tetyana National University of Kyiv-Mohyla Academy, Institute of agroecology, Ukraine
Show abstract
Soil moisture data is essential for planning agricultural activities, crop condition monitoring and drought prediction. InSAR remote sensing technology offers a means of measuring surface soil moisture, however temporal and spatial data resolution is crucial for effective remote sensing soil moisture data integration in decision making. NASA SMAP mission provides volumetric measurement of water content in surface soil with three day revisit time producing to the wide number of time series with global coverage. But since the loss of radar there are only low spatial resolution data products of 40 km is available from SMAP radiometer.
The aim of the research was to assess the feasibility of combined use of Sentinel-1 and SMAP data for soil moisture mapping. L3_SM_40km Gridded Radiometer Brightness Temperature / Soil Moisture and Sentinel-1A images were selected for merge application. The resulted merged data product time series were developed for the vegetation period (June – September 2016) and compared with the precipitation data from gauging stations over Ukraine (fig.1). The correlation of soil moisture distribution from merged SMAP/Sentinel-1 data was demonstrated. Developed soil moisture maps were included in weekly bulletin of environmental conditions for crop production.
Illustrations. Kuchma, Tetyana (2016): Soil Moisture maps of Ukraine obtained from SMAP satellite data. figshare. https://dx.doi.org/10.6084/m9.figshare.4109619.v2
[Authors] [ Overview programme] [ Keywords]
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Paper 400 - Session title: Poster Session 1
Tuesday-152 - Mapping Earthquake Damages From COSMO-SkyMed interferometric triplets
Grandoni, Domenico; Cardillo, Pier Francesco; Gentile, Vittorio; Minati, Federico; Britti, Filippo e-GEOS, Italy
Show abstract
The seismic sequence started in August 2016 and continued with significant shocks in late October 2016 has caused widespread damages to structures and buildings in a relatively large area in Central Italy. Thanks to its unmatched revisit capabilities and to a systematic acquisition plan monitoring Italian territory, COSMO-SkyMed constellation was able to deliver a number of SAR interferometric triplets composed by two images acquired before the earthquake and one image acquired after which allow mapping of earthquake damages based on the analysis of interferometric coherence changes over urban settlements (usually referred as Damage Proxy Map). The processing techniques is based on the identification of significan changes of interferometric coherence before and ater the event, therefore it requires a) the computation of the pre-seismic interferometric coherence b) the computation of the co-seismic interferometric coherence c) histogram matching of the two coherence layers d) calculation of the differences e) automatic masking out of non urban areas based on the Copernicus Land HRL Imperviousness layer f) statistical analysis of the differences in order to set the threshold for coherence difference relevancy. This technique has been successfully applied to differenct COSMO-SkyMed imaging modes (Spotlight-2 and Himage) both for the earthquake registered in August and for the one regstered in October, showing interesting results also when compared to damage data delivered by the Copernicus EMS Rapid Mapping service that are based on the analysis of very high resolution satellite and aerial optical data. This paper illustrates the results achieved in this specific case study and it provides a discussion of the topics to be addressed in order to bring SAR based Damage Proxy Map-like products to a level of operationality which is enough to sustain their inclusion in operational satellite based emergency mapping inititives such as the Copernicus EMS Rapid Mapping.
[Authors] [ Overview programme] [ Keywords]
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Paper 401 - Session title: Poster Session 1
Tuesday-36 - Interseismic deformation in the Mexican subduction zone, investigating for crustal deformation in the upper plate.
Pathier, Erwan (1); Rojo Limon, Graciela (1); Radiguet, Mathilde (1); Kostoglodov, Vladimir (2); Cotte, Nathalie (1); Walpersdorf, Andrea (1); Doin, Marie-Pierre (1); Volat, Matthieu (1) 1: Univ. Grenoble Alpes, France; 2: Universidad Nacional Autonoma de Mexico
Show abstract
The Mexican subduction zone extend along about 1000km at the Pacific coast of southern Mexico. Subduction interface is the place of largest earthquakes in the world that release seismically elastic energy accumulated for years because of tectonic plates convergences. In Mexico, like in many other countries close to active subduction zones, a better understanding and quantification of seismic hazard related to the subduction is a major scientific goals with significant societal impacts. The size and frequency of large subduction earthquakes is at first order mainly controlled by the relative plate convergence rate, which is quite constant in far field. However, a key remaining problem to address seismic hazard is that subduction zone, are significant spatial and temporal variations of slip behavior at the time scale of the seismic cycle.
Along the Mexican subduction zone instrumental seismicity has recorded several major (Mw>7) subduction earthquakes since the beginning of the 20th century, which are responsible of the large seismic hazard in Mexico. The Mexican subduction zone is also the place of slow earthquakes (SSE). The Guerrero and Oaxaca segments of the Mexican subduction zone are two well documented examples of such episodic slip events [e.g. Graham et al. 2015]. In Guerrero, they occurred almost every 4-years with an amount of slip equivalent to Mw7.5-7.6 earthquake.
Beside the subduction earthquake occurring on the plate interface, another source of hazard can come from earthquakes in the upper plate. Recently, the Chacalapa - La Venta Fault System (CLVFS), parallel to the trench, has been proposed to participate to the partitioning of the plate motion convergence (Gaidzik et al., 2016; Kostoglodov et al., 2014). We studied the possible activity of that fault system using geodetic observations and modelling. GPS time series analysis over the period 1998-2010 confirm the observation of Kostoglodov (2014), showing a signal compatible with a left-lateral slip of a few mm/year on the LVFS. The fault activity would occur mainly during the Slow slip events. However, due to the sparsity of the GPS network, it can not excluded that the signal could be alternatively explain by large spatial variations of the slip on the subduction interface below the fault trace. InSAR using ENVISAT data from 2003 to 2010 does not show a clear signal of fault activity. Comparison of INSAR observation with ground displacement predicted by fault model indicates that if the fault is active, slip on it is not occurring shallower than 5- 4 km. This results have to be confirm using Sentinel-1 and ALOS-2 data when a new SSE will occur.
[Authors] [ Overview programme] [ Keywords]
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Paper 403 - Session title: Poster Session 1
Tuesday-6 - Mid latitude ionosphere vs Synthetic Aperture RADAR imaging: case studies over Italy
Musicò, Elvira (1,2); Cesaroni, Claudio (2); Spogli, Luca (2,3); De Franceschi, Giorgiana (2); Seu, Roberto (1) 1: Sapienza University of Rome, Italy; 2: Istituto Nazionale di Geofisica e Vulcanologia (INGV); 3: SpacEarth Technology
Show abstract
The ionosphere is known to be particularly turbulent and irregular at high and low latitudes because of the effect of the geospatial environment and the interaction with the geomagnetic field. Also at mid-latitudes, the ionosphere can exhibit noticeable variability causing disturbances on a wide range of applications.
At these latitudes, the variability of the ionospheric environment during different passes of SAR causes an azimuth shift between the positions of the pixels of the master and slave images. This effect, also known as “azimuth streaks”, influences the optimal coregistration of the interferometric pair. In this paper, case studies in which the azimuth streaks occur are selected for ALOS-PALSAR images of central Italy. RINEX data from RING (Rete Integrata Nazionale GPS, http://ring.gm.ingv.it) are then used to derive regional maps of calibrated Total Electron Content (TEC) with suitable temporal and spatial resolution in order to investigate its variability in correspondence with the selected ALOS-PALSAR passages.
The analysis applied to selected case studies is here shown. The main steps of the analysis are:
The integral of the azimuthal shifts is evaluated, being proportional to the different TEC scenario between master and slave. This to overcome the issue that TEC gradients from RING along azimuth cannot be derived with sufficient accuracy, as TEC is the columnar value of the electron density between the satellite and the receiver.
The correlation between the integral of the azimuthal shifts and the InSAR phase is evaluated. For the selected case study, the InSAR phaseis assumed to be only due to the phase delay (tropospheric contribution) and to the phase advance(ionospheric contribution), acceptable in the absence of superimposed factors such as ground deformation.
Because correlation is found between the integral azimuthal shifts and the InSAR phase for the case studies under investigation, the tropospheric contribution to the latter is assumed negligible too. This follows the fact that the integral azimuthal shift is only proportional to TEC as coming from (1). Finally, TEC from InSAR phase can be evaluated and compared with TEC from RING. Details are given on the applied analysis method and on the quite encouraging results obtained.
[Authors] [ Overview programme] [ Keywords]
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Paper 407 - Session title: Poster Session 1
Tuesday-89 - Experience Application Data Of Sentinel-1 (TOPS) For The Determination Of Subsidence And Landslides In Urban And Non-urban Areas By PS-INSAR Technique
Nikitskii, Artem SCANEX Group, Russian Federation
Show abstract
The work describes the experience of application data of Sentinel-1 (TOPS) to determine the subsidence and landslides on several urban and non-urban areas on the territory of Russia by PS-INSAR technique for the period 2015-2016. Data processing was carried out using SARPROZ and Open source software. The results of processing the data of other satellites used to verify.
Feature data of Sentinel-1 (TOPS) requires a specific approach to their processing. Processing results confirm the possibility of use of Sentinel-1 (TOPS) data for monitoring subsidence and landslides.
As well as data from other satellites data of Sentinel-1 (TOPS) require special processing methods for non-urban areas where density of natural PS lower than urban. For non-urban areas good results have been achieved using the method of QPS. It is important for the territory of Russia, where large areas are not urbanized.
[Authors] [ Overview programme] [ Keywords]
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Paper 409 - Session title: Poster Session 1
Tuesday-118 - Autonomous Interferometric Calibration of Companion SAR Systems: Error Analysis and Performance Assessment
Rodriguez-Cassola, Marc (1); Prats, Pau (1); Lopez-Dekker, Paco (2); Nannini, Matteo (1) 1: DLR, Germany; 2: TU Delft
Show abstract
Companion SAR satellites offer a cost-effective alternative to enhance existing spaceborne SAR missions with a single-pass interferometric channel, paving the way to a number of new measurement capabilities including dynamic DEM monitoring, volume structure characterisation, or 2-D motion estimation. For their flexibility and versatility, companion SARs have been popular in the research community as a very attractive basis for future SAR mission concepts. ESA’s SAOCOM-CS mission is nothing but a proof of the former statement [1]. Like in any bistatic SAR, synchronous time and phase references of the monostatic and bistatic channels are essential. Typical time and phase accuracies in the order of picoseconds and a few degrees, respectively, are required in interferometric operation. In the case of TanDEM-X, this was achieved by means of a half-duplex direct link between transmitter and receiver [2]. Whenever a direct link is not available, the calibration of the time and phase references of the bistatic channel must be done using a data-based, i.e., autonomous algorithm. In previous references, we have suggested such a calibration concept for the SAOCOM-CS mission [3]. The autonomous interferometric calibration follows a two-step approach, at SLC and interferogram level. The SLC synchronisation is effected with help of the reference monostatic channel using an AutoSync algorithm. The residual calibration of the interferogram follows with help of an external DEM. The asymptotic performance of the algorithm shows very good accuracy in typical cases assuming sufficient knowledge of external error sources other than clocks, as shown in the figure below.
[Authors] [ Overview programme] [ Keywords]
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Paper 410 - Session title: Poster Session 1
Tuesday-96 - Demonstrating The Value Of Commercial SAR Data In A Sentinel-1 World
Thomas, Adam Mark; Holley, Rachel CGG Services (UK) Limited, United Kingdom
Show abstract
As Sentinel-1 satellites enter routine operations, the InSAR community has gained access to a highly capable source of data. Spatial coverage is unprecedented and, as capacity expands, the acquisition schedule will span the globe with regular, dependable SAR data.
Sentinel-1 data has resulted in a step-change in the capabilities of InSAR, opening up a wider range of applications and new technical possibilities. Free data access makes developments affordable and accessible, both for research and commercial exploitation, and as the available archive of data builds, the use of Sentinel-1 will undoubtedly expand.
Although Sentinel-1 represents an advancement in radar remote sensing, there will always remain trade-offs relating to its ability to address ground stability challenges. Other sources of SAR data, such as X- and L-band imagery, have the ability to provide complementary measurements, or may even be better suited than Sentinel-1 in meeting the task at hand. The result isn’t a market dominated by this freely available source of data, rather it’s a market underpinned by a wide range of SAR data, accessible in historical archives and via satellite tasking, and capable of meeting the diverse needs of its users.
This paper presents a series of case studies that demonstrate how commercially available SAR data can supplement data from Sentinel-1. These include applications that benefit from very high resolution SAR imagery, acquisitions with different incidence angles or from opposing tracks, and acquisitions at longer wavelengths. Other SAR sensors also have the potential to complement Sentinel-1 data in areas of the world where acquisitions are (currently) less frequent, and also include archives of historical data to extend analyses over longer periods of time.
[Authors] [ Overview programme] [ Keywords]
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Paper 414 - Session title: Poster Session 1
Tuesday-142 - Volcanic activity analysis of Mt. Sinabung in Indonesia using InSAR and Laharz model
Lee, Changwook (1); Lu, Zhong (2); Lee, Moungjin (3) 1: Kangwon National University, Korea, Republic of (South Korea); 2: Southern Methodist University; 3: Korea Environment Institute
Show abstract
Sinabung volcano, Indonesia, was formed due to the subduction between the Eurasian and Indo-Australian plates along the Pacific Ring of Fire. After being dormant for about 400 years, Sinabung volcano erupted on 29 August 2010 and recently on 4 January 2014. We studied the deformation of Sinabung volcano using Advanced Land Observing Satellite/Phased Array type L-band Synthetic Aperture Radar (ALOS/PALSAR) interferometric synthetic aperture radar (InSAR) images acquired from February 2007 to January 2011. Based on multi-temporal InSAR processing, we mapped the ground surface deformation before, during, and after the 2010 eruption. During the 3 years before the 2010 eruption, the volcano inflated at an average rate of ~1.7 cm/yr with a markedly higher rate of 6.6 cm/yr during the 6 months prior to the 2010 eruption. The inflation was constrained on the top of the volcano. From the 2010 eruption to January 2011, the volcano subsided by about 3 cm (or ~6 cm/yr). The observed inflation and deflation were modeled with a Mogi and prolate spheroid source. The source of inflation was located about 0.3–1.3 km below sea level directly beneath the crater. On the other hand, during the coeruption period, the deflation source was modeled at 0.6–1.0 km depth. The average volumetric change was approximately −2.7 × 10-5 to 1.9 × 10-6 km3/yr during the deformation event. The modified Laharz model was compared to the Landsat-7 Enhanced Thematic Mapper plus (ETM+) image through. We interpreted that the inflation was due to magma accumulation in a shallow reservoir beneath Sinabung. The deflation was attributed to magma withdrawal from the shallow reservoir during the eruption as well as thermo-elastic compaction of erupted material. The pyroclastic flow inundation area was highly matched between the two different methods with about 86% common region inserting the deflation pattern of volume (2.7 × 10-5 km3) by the Mogi model.
[Authors] [ Overview programme] [ Keywords]
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Paper 417 - Session title: Poster Session 1
Tuesday-66 - Evaluation of InSAR-derived TanDEM-X elevation data and applications in coastal vulnerability mapping
Li, Peng (1,2); Li, Zhenhong (3); Feng, Wanpeng (4); Dai, Keren (5); Al-Husseinawi, Yasir (3); Chen, Jiajun (3); Wang, Houjie (1,2) 1: Key Lab of Submarine Geosciences and Prospecting Techniques, Ministry of Education, Qingdao, China; 2: College of Marine Geosciences, Ocean University of China, Qingdao, China; 3: COMET, School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, UK; 4: Canada Center for Mapping and Earth Observations, Natural Resources Canada, Ottawa, Canada; 5: Department of Remote Sensing and Geospatial Information Engineering, Southwest Jiaotong University, Chengdu, China
Show abstract
Use of high-accuracy elevation data is an advantage for elevation-based assessments of coastal inundation events (e.g. storm surges, abnormal high tides, or extreme precipitation events). In this study, we attempt to assess the quality of the 6m-spatial-resolution TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurements) DEM derived from TanDEM-X CoSSC (Coregistered Single look Slant range Complex) data over different areas in China. Three study sites are chosen in this study, including the Three Gorges area, the Wenchuan earthquake area and the Qingdao coastal area. The distinctly different geographical locations of these study sites ensure their spatial independence and different topography features. All the TanDEM-X DEMs over the study areas were generated with the GAMMA software. Since the CoSSC data are already coregistered, the main steps for DEM generation are the following: interferogram generation, phase removal, phase unwrapping, absolute phase calibration, geocoding. Then we analyzed the correlation between height differences (DEM-GPS, DEM-ICESat, DEM-GDEM) and DEM derivatives (slope and aspect) from elevation. Furthermore, the results were separated into land cover classes from the 300m ESA GlobCover dataset to derive the spatial patterns of error of the TanDEM-X DEM. Finally, we evaluated the potential of TanDEM-X DEM for coastal vulnerability mapping in the Qingdao coastal area, East China, in order to investigate the effect of the accuracy and resolution of coastal topography on the reliability and usefulness of elevation-based sea-level rise assessments.
[Authors] [ Overview programme] [ Keywords]
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Paper 420 - Session title: Poster Session 1
Tuesday-108 - Large scale InSAR monitoring of permafrost freeze-thaw cycles on the Tibetan Plateau
Daout, Simon (1); Doin, Marie-Pierre (2); Socquet, Anne (2); Peltzer, Gilles (3); Lasserre, Cécile (2) 1: University of Kiel, Germany; 2: Université Grenoble-Alpes, France; 3: University of California, LA, USA
Show abstract
Monitoring surface deformation by multi temporal InSAR (MT-InSAR) observations is an effective way of mapping ground freeze-thaw cycles and characterizing the underlying permafrost temporal evolution. However, the approach is generally limited by the decorrelation of the radar phase over surfaces with changing conditions and steep deformation gradients. Here, we develop a method to circumvent these limitations and construct an 8-year timeline of continuous surface deformation maps over a 60,000 km2 area in Northwestern Tibet. Response of active layer to climate forcing is spatially variable for both amplitude (2.5 to 12 mm) and multi-annual trend (-2 to 3 mm/yr), but is limited to elongated Cenozoic sedimentary basins. Diffusive models do not explain the observations that show that the average maximum ground thawing occurs in mid October, after the return of freezing diurnal temperatures. Large amplitude (>8 mm) and early timing (end September) of the ground movement corresponds to large water availability in the active layer whereas lower amplitudes and later timing (early November) indicate that freezing and thawing occur deeper in a less saturated soil. The spatially variable multi-annual velocity trend is influenced by elevation and possible decadal changes of meltwater supply and drainage conditions during the summer. MT-InSAR technique demonstrates his potential for a systematic spatio-temporal measurement of essential permafrost distribution and properties that will be extremely valuable as input to models of climate change.
[Authors] [ Overview programme] [ Keywords]
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Paper 421 - Session title: Poster Session 1
Tuesday-100 - Deglaciation-induced uplift of the Petermann glacier ice margin observed with InSAR
Lu, Qianyun (1); Amelung, Falk (1); Wdowinski, Shimon (2) 1: University of Miami, United States of America; 2: Florida International University, United States of America
Show abstract
The Greenland ice sheet is rapidly shrinking with the fastest retreat and thinning occurring at the ice sheet margin and near the outlet glaciers. The changes of the ice mass cause an elastic response of the bedrock. Ice mass loss during the summer months is associated with uplift, whereas ice mass increase during the winter months is associated with subsidence.The German TerraSAR-X and TanDEM-X satellites have systematically observed selected sites along the Greenland Petermann ice sheet margin since summer 2012. Here we present ground deformation observations obtained using an InSAR time-series approach based on small baseline interferograms. Deformation observed by InSAR is consistent with GPS vertical observations. The time series displacement data reveal not only net uplift but also the seasonal variations.
[Authors] [ Overview programme] [ Keywords]
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Paper 422 - Session title: Poster Session 1
Tuesday-37 - Going To Any Lengths: Solving for Slip and Fault Size in Mw 6.2 Kurayoshi, Japan, 2016 Earthquake
Amey, Ruth M.J.; Hooper, Andy J.; Spaans, Karsten H. University of Leeds, United Kingdom
Show abstract
Many earthquake properties show self-similar (fractal) features. We have previously developed a method to incorporate this self-similarity into earthquake slip distributions. We do this by performing a Bayesian slip inversion on coseismic InSAR and GPS surface displacements and incorporating the von Karman autocorrelation function as a regularising function, which captures the fractal nature of slip.
One major difference in using the von Karman regularisation rather than commonly used Laplacian smoothing is that each patch has a relationship to every other patch. This is advantageous because it means that poorly resolved slip patches at depth can be better resolved due to their relationship with better constrained patches at the surface. But this means that the choice of fault length and width is particularly important; in most slip inversions fault plane extent is chosen in advance and then slip is solved for on these planes. This means that the final slip solution depends upon this geometry choice.
Here we present a method for solving the size of the fault plane during the slip inversion process, as well as slip, rake and dip. We apply this method to the Mw 6.2 Kurayoshi, Japan, 2016 earthquake using Sentinel-1 and GPS data. The earthquake ruptured a north-south orientated left-lateral strike-slip fault in northern Tottori. We present our solution of the slip inversion including the length and width of the fault and comment on the implications for regional hazard.
[Authors] [ Overview programme] [ Keywords]
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Paper 423 - Session title: Poster Session 1
Tuesday-38 - Crustal Deformation Caused by Large Earthquakes in Japan, Italy and New Zealand in 2016 Observed by ALOS-2
Morishita, Yu; Kobayashi, Tomokazu; Yarai, Hiroshi; Fujiwara, Satoshi; Nakano, Takayuki; Miura, Yuji; Ueshiba, Haruka; Kakiage, Yasuaki; Honda, Masaki; Nakai, Hiroyuki; Miyahara, Basara; Une, Hiroshi Geospatial Information Authority of Japan, Japan
Show abstract
1. Introduction
Advanced Land Observing Satellite 2 (ALOS-2) is an L-band synthetic aperture radar (SAR) satellite, launched by Japan Aerospace Exploration Agency (JAXA) on 24 May, 2014. Observation capability of ALOS-2 is higher than that of ALOS, the predecessor of ALOS-2 and operated from 2006 to 2011, in terms of a revisit cycle (ALOS-2: 14 days, ALOS: 46 days) and attainable spatial resolution (ALOS-2: 3 m, ALOS: 10 m). Moreover, ALOS-2 can observe not only by common right-looking but also by left-looking, and ScanSAR interferometry is always applicable, unlike ALOS. These improvements enhances detection capability of crustal deformation.
Sentinel-1A and 1B, which are C-band SAR satellites, were also launched by European Space Agency (ESA) on 3 April, 2014 and 25 April, 2016, respectively. They have several advantages over ALOS-2, such as a shorter revisit cycle and wider swath width of a standard observation mode, resulting in great achievements for deformation monitoring. However, ALOS-2 often shows better capability in the field of an earthquake observation because ALOS-2 can obtain higher coherence over a wide area including vegetated areas owing to the L-band and can detect surface displacement which is often hampered by severe decorrelation with the view of Sentinel-1.
In this presentation, we will report four case studies of crustal deformation caused by large earthquakes in 2016 detected by ALOS-2.
2. Kumamoto earthquake sequence, Japan (14 April, Mj 6.5; 15 April, Mj 7.3) (Geospatial Information Authority of Japan (GSI), 2016a; GSI, 2016b)
This earthquake sequence occurred along the Futagawa fault and the Hinagu fault. At the start of the earthquake sequence, a foreshock (Mj 6.5) occurred on 14 April, 12:26. ALOS-2 promptly responded and observed around the epicenter by left-looking on 15 April, 03:52, only 15.5 hours after the foreshock. Clear surface displacement was detected by applying SAR interferometry (InSAR) and Multiple Aperture Interferometry (MAI), and implied a right-lateral fault motion along the Hinagu fault.
On 15 April, 16:25, 28 hours after the foreshock, much larger main shock (Mj 7.3) occurred. A lot of observations from various directions (i.e., ascending/descending, right-looking/left-looking) with various incidence angles were conducted by ALOS-2 after the main shock. Very extensive and large surface displacements was detected by applying InSAR, MAI, and a Pixel Offset method. Three dimensional (3D) displacement fields have been retrieved by combining multiple line-of-sight (LOS) and azimuth displacements with different geometry, and revealed horizontal displacement gaps over 2 m and subsidence over 2 m along the Futagawa fault. An estimated fault model indicates four fault planes slipped mainly right laterally.
Numerous discontinuities of differential phases in InSAR images, representing surface ruptures, were discovered extensively (Fujiwara et al., 2016). Although some of them are coincide with the positions of known active faults, the number of the discovered discontinuities is much larger than that of the known active faults. Around northwest of the outer rim of the Aso caldera, particularly, parallel discontinuities with the strike of WNW-ESE are densely found. We manually unwrapped the InSAR images acquired from four different observing directions (i.e., combination of ascending/descending and right-/left-looking), retrieved 3D displacement fields (Morishita et al., 2016), removed a long wavelength displacement component due to the main fault motion by applying high-pass filter, and finally found a characteristic vertical displacement pattern which suggested graben formation.
3. Italy earthquake sequence (24 August, Mw 6.2; 26 October, Mw 6.1; 30 October, Mw 6.6) (GSI, 2016c; GSI, 2016d)
Emergency observations were conducted responding to the earthquake in August (Mw 6.2) in central Italy by ALOS-2 from two different directions (i.e., ascending and descending). InSAR and 2.5 dimensional analysis (decomposition of two LOS displacements into quasi-EW and quasi-vertical) revealed that subsidence and westward displacement of 20 cm at a maximum occurred with the length of 20 km in NNW-SSE direction. The displacement pattern suggests a normal fault with the strike of NNW-SSE.
On 26 October, two months after the earthquake in August, a large earthquake (Mw 6.1) occurred at the area adjacent to the deforming area of the previous earthquake in August on the north side. ALOS-2 InSAR shows similar amount and pattern of the displacement, which implies that the mechanisms of these two earthquakes are almost corresponding. The deforming areas are not overlapping, i.e., there was a gap area with no deformation.
Other 3.5 days after, the largest earthquake (Mw 6.6) among this earthquake sequence occurred at the area between the previous two earthquakes. Much larger displacement than that of previous earthquakes was measured by ALOS-2 InSAR, while the pattern of the displacement is similar. The gap area of the previous earthquakes shows very complicated phase changes meaning that disordered deformation occurred, and is supposed to be ruptured by the largest earthquake.
4. Tottori earthquake, Japan (21 October, Mj 6.6) (GSI, 2016e)
Emergency observations of ALOS-2 were successively conducted after a large earthquake (21 October, Mj 6.6) in Tottori, Japan, resulting in acquisitions of InSAR images from four different directions (i.e., combination of ascending /descending and right-/left-looking) only five days after the earthquake. Estimated 3D displacement from the four InSAR images shows very clear and pure four-quadrant displacement pattern which is theoretically well explained by a left-lateral fault motion with the strike of NNW-SSE, though the amount of the displacement is only ~10 cm. The standard errors of the estimated 3D displacement are ~1 cm for the EW and UD components and ~4 cm for the NS component. This high precision of the 3D displacement is not possible without four InSAR images with different observing geometry exploiting not only right-looking but also left-looking, i.e., impossible by only Sentinel-1 whose observations are only right-looking, but possible only by ALOS-2 and only in Japan region where the left-looking data have already been acquired at present.
5. Kaikoura earthquake, New Zealand (13 November, Mw 7.8) (GSI, 2016f)
A large earthquake (Mw 7.8) occurred in New Zealand on 13 November. Surface ruptures and coastal uplift over a wide area were reported soon after the earthquake, therefore it was expected that very large and complicated crustal deformation occurred. ALOS-2 observed not only by a Stripmap mode which have high spatial resolution, but also ScanSAR mode with a wide swath, and revealed an overall image and details of the crustal deformation.
Clear discontinuities of the displacement were detected along the Kekerengu fault and Jordan thrust in the 3D displacement field estimated from the results of the Pixel Offset method. Along the Kekerengu fault, uplift at the north side and right-lateral strike-slip occurred, and its amount reaches ~10 m. Along the Jordan thrust, uplift at the south side and right-lateral strike-slip occurred. Another clear discontinuity is also found from the south edge of the Kekerengu fault (north edge of the Jordan thrust) with the conjugate strike. At the west side, ~10 m uplift at a maximum and over 6 m southward displacement were detected.
We will also report details of the crustal deformation around south of the Hope fault and fault models.
* The time is based on UTC. Mw according to United States Geological Survey (USGS) and Mj according to Japan Meteorological Agency (JMA).
References
Geospatial Information Authority of Japan (2016a), Information about the 2016 Kumamoto earthquake (in Japanese), http://www.gsi.go.jp/BOUSAI/H27-kumamoto-earthquake-index.html.
Geospatial Information Authority of Japan (2016b), The 2016 Kumamoto Earthquake: Crustal deformation around the faults, http://www.gsi.go.jp/cais/topic160428-index-e.html.
Geospatial Information Authority of Japan (2016c), The August 2016 Central Italy Earthquake: Crustal deformation detected by ALOS-2 data, http://www.gsi.go.jp/cais/topic160826-index-e.html.
Geospatial Information Authority of Japan (2016d), The October 2016 Central Italy Earthquake: Crustal deformation detected by ALOS-2 data, http://www.gsi.go.jp/cais/topic161108-index-e.html.
Geospatial Information Authority of Japan (2016e), The 2016 Central Tottori Earthquake, http://www.gsi.go.jp/cais/topic161027-index-e.html.
Geospatial Information Authority of Japan (2016f), The 2016 New Zealand Earthquake: Crustal deformation detected by ALOS-2 data, http://www.gsi.go.jp/cais/topic161117-index-e.html.
Fujiwara, S., H. Yarai, T. Kobayashi, Y. Morishita, T. Nakano, B. Miyahara, H. Nakai, Y. Miura, H. Ueshiba, Y. Kakiage and H. Une (2016), Small-displacement linear surface ruptures of the 2016 Kumamoto earthquake sequence detected by ALOS-2 SAR interferometry, Earth Planets Space, 68: 160.
Morishita, Y., T. Kobayashi, and H. Yarai (2016), Three-dimensional deformation mapping of a dike intrusion event in Sakurajima in 2015 by exploiting the right- and left-looking ALOS-2 InSAR, Geophys. Res. Lett., 43.
[Authors] [ Overview programme] [ Keywords]
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Paper 427 - Session title: Poster Session 1
Tuesday-112 - Radar signal penetration into glaciers and its implications - Case studies of two glacierized catchments in Alaska and Himalayan region
Vijay, Saurabh; Braun, Matthias FAU Erlangen-Nuremberg, Germany
Show abstract
SAR data has proven to be an effective tool to map surface topography and geodetic measurements (elevation and mass change) of glaciers. For instance, the SRTM C-and X-band and TanDEM-X (X-band) are two potential radar missions for such measurements. The TanDEM-X is an ongoing mission with high spatial and temporal resolution. In the first case study, we select Columbia Glacier, Alaska to empirically estimate X-band penetration depth under different glacier surface conditions. For this, we compare TanDEM-X DEMs with surface elevation measured from the NASA's Operation IceBridge campaigns during 2011-2012. We find altitude dependent X-band penetration depth in both summer and winter conditions. In summers, the penetration depth varies from ~ 0 m (~200 m of altitude) to ~8 m (~2800 m of altitude) (Figure 1). The X-band signal penetrates comparably more in winters and varies from ~4 m to ~25 m (Figure 1). These estimates are explained by the fact that the glacier surface at lower altitudes (below transient snow line) contains liquid water in summers which attenuates the radar signal to penetrate. However, the presence of fresh snow cover at these altitudes can act as a transparent medium for a radar signal which leads to volume scattering.
Similarly, in a second case study, we empirically estimate the SRTM C- and X-band penetration differences for various surface types (debris-covered ice, clean ice/firn/snow) in the Himalayan region. This also reveals a clear altitude dependent trend of penetration difference over clean ice/firn/snow with maximum difference at high altitudes. We correct our elevation change measurements (TanDEM-X of 2012 minus SRTM C-band of 2000) for this penetration difference bias. We find that this bias, if not corrected, underestimates the region-wide elevation and mass change measurements by 20 %. We suggest that more such studies need to be be carried out to either empirically estimate or model the radar (X-, C- or L- band) penetration depth in different surface conditions of glaciers. This provides a valuable information about the precise measurements of the surface topography and geodetic variables using ongoing or future bistatic missions.
[Authors] [ Overview programme] [ Keywords]
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Paper 429 - Session title: Poster Session 1
Tuesday-39 - Monitoring Of Surface Deformation Over Vrancea Seismotectonic Area In Romania Through Time Series Analysis of GPS and radar data
Zoran, Maria (1); Savastru, Dan (1); Serban, Florin (2); Teleaga, Delia (2); Mateciuc, Doru (3) 1: National Institute of R&D for Optoelectronics, Romania; 2: TERRASIGNA SRL Romania; 3: National Institute of R&D for Earth Physics. Romania
Show abstract
Space-based observations, coupled with surface in-situ observations where available, can enable scientists to survey large surface areas for precursory signals, allowing the monitoring of broad areas of the surface of the earth where strong earthquakes can be expected to occur. Time series analysis of Global Positioning Systems GPS and InSAR data is an important tool for Earth’s surface deformation, which can result from a wide range of geological phenomena like as earthquakes, volcanoes, landslides or ground water level changes. The study of geophysical phenomena which appear prior to and after seismic events involves different scientific fields like geophysics, hydrology, geomagnetism, atmospheric physics, geochemistry, radiopropagation and seismology. Earthquake prediction has two potentially compatible but distinctly different objectives: (a) phenomena that provide information about the future earthquake hazard useful to those who live in earthquake-prone regions and (b) phenomena causally related to the physical processes governing failure on a fault that will improve our understanding of those processes. To understand the exact relationship of a precursor with an impending large earthquake, it is essential to know the geodynamical reason behind the occurrence of that precursor. Validating an earthquake precursor through an acceptable geodynamic modeling and accounting for its occurrence is a challenging task. The aim of this paper was to identify several types of earthquake precursors that might be observed from geospatial data. Precise information concerning surface deformation of the earth in Vrancea region is indispensable to numerical simulation of earthquakes and of other tectonic activity. Surface deformation can be interpreted in relation to an internal mechanical process of the Earth, i.e., stress distribution or fault slips, using the elastic dislocation theory. In spite of providing the best constraints on the rate of strain accumulation on active faults (coseismic, postseismic, and interseismic deformation; plate motion and crustal deformation at plate boundaries), GPS measurements have a low spatial resolution, and deformation in the vertical direction cannot be determined very accurately. Continuous GPS Romanian network stations and few field campaigns data between 2005-2012 revealed a displacement of about 5 or 6 millimeters per year in horizontal direction relative motion, and a few millimeters per year in vertical direction. In support of this achievement , time series satellite Sentinel 1 data available for Vrancea zone during October 2014 till October 2016 have been used to generate two types of interferograms (short-term and medium- term) in order to assess possible deformations due to earthquakes and respectively for possible slow deformations. As during last investigated period have not been recorded medium or strong earthquakes, interferograms over investigated test area revealed small displacements on vertical direction (subsidence or uplifts) of 5-10 millimeters per year. Based on GPS continuous network as well as satellite Sentinel 1 results, different possible tectonic scenarios can be developed. The localization of horizontal and vertical motions, fault slip, and surface deformation of the continental blocks provides new information, in support of different geodynamic models.As Vrancea area has a significant regional tectonic activity in Romania and Europe, the joint analysis of geospatial and in-situ geophysical information is revealing new insights in the field of hazard assessment.
[Authors] [ Overview programme] [ Keywords]
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Paper 433 - Session title: Poster Session 1
Tuesday-74 - Strategies To Improve The Goldstein Filter for SAR Interferometric Phase
Mestre, Alejandro (1); Lopez-Sanchez, Juan M (1); Selva, Jesus (1); Gonzalez-Mendez, Pablo J. (2) 1: University of Alicante, Spain; 2: University of Liverpool, United Kingdom
Show abstract
The well-known Goldstein filter [Goldstein98] is used frequently by the geophysics community to improve the quality of phase in differential interferograms. Since its conception, a number of algorithms has been proposed to improve its performance. The main strategy is based on modifying the parameters of the filter (alpha exponent and window size) as a function of the local features of the interferometric phase (coherence, presenec of gradients, etc.). The most recent example of this type of improvements was pro posed by Suo et al. [Suo16]. Alternatively, a recursive Goldstein filter was proposed in [Gonzalez14]. In this case, the interferogram is filtered a number of times by using decreasing window sizes.
The recursive strategy has proven its good performance over very noisy interferograms (even with coherences below 0.3), but it can overfilter (i.e. smoothen) very detailed features. In the other hand, the locally-adaptive strategy employed in [Suo16] exhibits good results over detailed areas (i.e. small size features) but do not get the same phase quality as the recursive apporach over wide areas with low frequency (i.e. it filter less than the recursive approach).
In this work we have implemented and evaluated both filtering strategies. Then we have proposed some ways to combine the best aspects of both strategies. First results are obtained both with synthetic data and real data acquired by Radarsat-2 and TerraSAR-X.
References:
[Goldstein98] R. M. Goldstein, C. L. Werner, "Radar interferogram filtering for geophysical applications", Geophysical Research Letters, Vol. 25, No. 21, pp. 4035-4038, Nov. 1998.
[Gonzalez14] P. J. Gonzalez, "A recursive adaptive spectral interferogram phase filtering method", in Proceedings of Wegener2014, Leeds, UK, Sept. 2014.
[Suo16] Z. Suo et al., "Improved InSAR Phase Noise Filter in Frequency Domain", IEEE Trans. on Geoscience and Remote Sensing, Vol. 54, No. 2, pp. 1185-1195, Feb. 2016.
[Authors] [ Overview programme] [ Keywords]
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Paper 440 - Session title: Poster Session 1
Tuesday-103 - Ground-Based Radar Measurements For The Investigation Of Calving Glacier Dynamics
Rouyet, Line (1); Strozzi, Tazio (2); Tom Rune, Lauknes (1) 1: Norut, Norway; 2: Gamma Remote Sensing, 2073 Gümligen, Switzerland
Show abstract
A good understanding of tidewater glaciers and icebergs dynamics is essential for the management of shipping operations under arctic conditions and the interpretation of environmental processes in a context of climate change. This requires consistent datasets and long time series that can be challenging to acquire in harsh and remote arctic areas. In this context, remote sensing technologies provide opportunities in the mapping and monitoring of the cryosphere and the Arctic Ocean.
We contribute to research in this field and have been part of several projects in Ny-Ålesund (Svalbard) for the collection and analysis of data over Kongsfjorden and Kronebreen. In August 2016, a campaign has been performed as part of the CalvingSEIS Experiment project. It included two ground-based radar systems (Gamma Portable Radar Interferometer - GPRI) acquiring images from the shore at the front of Kronebreen. One ground-based radar has been set to image continuously the whole front every two minutes. The second ground-based radar focused on smaller sections of the glacier front with a temporal resolution that was continuously reduced from minutes to seconds and hundredths of a second to catch calving events. The first GPRI provide large-scale velocity maps and contribute to inventory calving events. The results provide moreover information about iceberg dynamics in the fjord. The second is less sensitive to decorrelation and allow the precursors of calving events to be measured. In addition, the second system has been moved to the opposite shore during some hours to provide another view angle. The results from two line-of-sight were combined to estimate 2 dimentional vectors of movement under the assumption of horizontal motion
Thanks to a wide partnership, the datasets can be compared and combined with in-situ data, complementary remote sensing data, and interpreted by experts in glaciology and oceanography. The results highlight the great potential of remote sensing technologies in Svalbard and the value to combine satellite, airborne and ground-based devices to provide complementary spatio-temporal coverages and resolutions, as well as integrate the different advantages of each system.
[Authors] [ Overview programme] [ Keywords]
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Paper 442 - Session title: Poster Session 1
Tuesday-86 - InSAR And GPS Time Series Analysis Along The North Anatolian Fault Zone
Benoit, Angelique (1); Jolivet, Romain (1); Cakir, Ziyadin (2); Ergintav, Semih (3); Fattahi, Heresh (4); Dogan, Ugur (5) 1: Ecole Normale Superieure, Department of Geology, France; 2: Istanbul Technical University, Department of Geology, Turkey; 3: Bogazici University, Department of Geology, Turkey; 4: Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125 USA; 5: Yildiz Technical University, Department of Geodesy, Turkey
Show abstract
Over the earthquake cycle, most major fault segments are locked most of the time, accumulating strain imposed by the continuous motion of plate tectonics, and release the corresponding elastic stress during large earthquakes. On other fault segments, slip can be dominantly aseismic (i.e. the fault is creeping) with significant implications on the slip budget of the fault. The seismic behaviour of active faults is controlled by various factors, including the spatial distribution of rheological properties and the spatio-temporal evolution of stress in crust. In addition, the aseismic behavior of a fault has a significant influence on the nucleation, the propagation and the arrest of seismic ruptures.
The central segment of the North Anatolian fault is known to be creeping at least since the fault ruptured during the 1944, M7.3, earthquake. Since then, this 80 km-long-section slips aseismically at a velocity of 7-8 mm/yr, as predicted by the dynamic model developed for this fault section. Up to now, it was thought that slip was at a constant rate. Both data from the SAR satellite constellation Cosmo-SkyMed and from a creepmeter installed in the city of Ismetpasa have shown recently that aseismic slip is not constant with days- to month-long slip episodes, hence calling for a new physical description of slip along this fault.
Until now, the monthly return period of previous satellite constellations (ALOS, ERS, ENVISAT) and the non-systematic acquisition planning resulted in scarce time series, not dense enough to capture these slow slips events systematically. The recent launch of the Sentinel 1 A and B satellites, respectively on 3 April 2014 and 25 April 2016, represents a good opportunity to measure the surface deformation finely and describe the temporal evolution of shallow aseismic slip with unprecedented spatial and temporal detail. Acquisitions are made every 6 days and cover a wide area (100x300 km) thanks to TOPS mode acquisition, thus allowing to capture transient events. Furthermore data are openly accessible.
This large database, with a high temporal sampling, allows us to perform an InSAR time series analysis. Then, we model surface displacements to quantify deep aseismic slip along the fault. In addition, we have installed in July 2016 five continuous GPS stations in the vicinity of the creeping zone, complementing the GPS station already in place at Ismetpasa. We compare the InSAR-derived displacements with the continuous GPS measurements, providing a finer temporal resolution of the evolution of shallow aseismic slip. These results, both from InSAR time series and GPS, will provide a better understanding of the regional seismogenic behavior of the North Anatolian fault and eventually allow us to study the fault zone properties and the mechanical model of this major active fault.
[Authors] [ Overview programme] [ Keywords]
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Paper 449 - Session title: Poster Session 1
Tuesday-40 - Monitoring Fault Activities of the Northeastern India Area Using Persistent Scatterer Interferometry and Sentinel-1 SAR Data
Lee, Jui-Chi (1); Chang, Chung-Pai (1); Yhokha, Akano (1); Manini, Aruche K. (1); Yen, Jiun-Yee (2) 1: National Central University, Taiwan, Republic of China; 2: National Dong Hwa University, Taiwan, Republic of China
Show abstract
This study contributes to tectonic questions of northeastern India by using the technique of persistent scatterer Interferometry (PSI). The northeastern India is a tectonically active region, where the geomorphophic development is a consequence of collision between the Indian subcontinent and the Tibetan plateau in the north and the subduction between Indian-Australia plate and Myanmar plate in the east. The present tectonic configuration of the region is due to the north and northeast ward movement of the Indian plate between the Chagos- Laccadive transform and the Ninety Degree East rift. The north-western part of Nagaland is characterized by a Schuppen Belt, an imbricate structure following recumbent folds. Nowhere in north-east India, have the compressive force made so much impact as in Nagaland. Thus, the natural tectonic setting of Nagaland offers an ideal location to study the active tectonic movements and to monitor the present surface deformation. Various aspects in geology of the region had been studied earlier by several workers, however the application of advanced Remote Sensing based studies are lacking. Therefore, in this study we intend to use the Sentinel-1 data. The new C-band synthetic aperture radar (SAR) sensor on board the Sentinel-1 mission satellites is an effective sensor system for monitoring crustal deformation over extensive areas including mountainous areas and as an important tool for exploring the mechanism of fault movements. Our results will give a systematic understanding and insights about the structural complexity of the tectonically active regions, as the natural tectonic settings make the region very prone to hazards, such as landslides, land subsidence and earthquakes.
[Authors] [ Overview programme] [ Keywords]
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Paper 450 - Session title: Poster Session 1
Tuesday-41 - Surface creep along the East Anatolian Fault (Turkey) revealed by Envisat and Sentinel-1 InSAR time series
Senturk, Selver (1); Cakir, Ziyadin (1); Ergintav, Semih (2); Dogan, Ugur (3); Cetin, Seda (3) 1: Istanbul Technical University, Turkey; 2: Bogazici University, Turkey; 3: Yildiz Technical University, Turkey
Show abstract
InSAR studies over the last decade have demonstrated that contrary to the general belief surface creep along active faults is not a rare, but a common phenomenon and observed along numerous continental strike slip faults. Our InSAR observations along the East Anatolian fault (EAF) have revealed that the EAF is creeping too. Forming the boundary between the Anatolian and Arabian plates in Turkey, the EAF is one of the most important tectonic structures in the Eastern Mediterranean region. Together with its conjugate, the North Anatolian Fault (NAF), it accommodates the westward motion of the Anatolian plate at a rate of ~10 mm/y (Reilinger et al., 2006). We mapped the interseismic velocity field along the eastern section of the EAF using Envisat (2002-2010) and Sentinel-1 (2014-2016) SAR data. Three adjacent descending and overlapping Envisat (T035, T264 and T493) and two Sentinel (descending T123 and ascending T43) tracks are used to calculate the velocity field using the Stanford Method for Persistent Scatterers technique (STAMPS; Hooper et al., 2012). The results reveal that the 100-km-long Palu segment in the Elazıg-Bingöl seismic gap is exhibiting aseismic creep at the surface. The creep rate varies along the fault reaching, at some places, to the far field plate velocity (i.e., 10 mm/y), implying that significant portion of the elastic strain has been released aseismically. Preliminary modelling with elastic dislocations suggests that some sections of the fault may be creeping from surface down to the entire seismogenic crust. Geology of the fault zone is dominated by ophiolitic and volcanic rocks characterized by weak phyllosilicate minerals, suggesting that aseismic slip is promoted by minerals with low frictional properties.
[Authors] [ Overview programme] [ Keywords]
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Paper 456 - Session title: Poster Session 1
Tuesday-42 - Subsidence, Stress and Induced Seismicity: Example From a Hydropower Reservoir in Norway
Keiding, Marie (1); Dehls, John F (1); Lauknes, Tom Rune (2) 1: Geological Survey of Norway, Norway; 2: Norut, Norway
Show abstract
Storglomvatnet is Norway's largest hydropower reservoir, with a capacity of 3 500 Mm³. It is located adjacent to a large glacier called Svartisen. Dam construction was completed in 1997, and over the next three years, the water level was raised by 125 m (approx 2 500 Mm³). A significant increase in seismicity occurred in the region in 1998 and the levels remained high until 2003.
Data from three overlapping ERS tracks has been used to analyse the subsidence caused by the filling of the reservoir, and investigate its role in triggering seismic events. Temporal sampling of the deformation is rather sparse, due to infrequent acquisitions and the inability to use winter scenes with snow cover. Nonetheless, subsidence during the period of reservoir filling is clearly visible, affecting a NE-SW elongated region of approximately 80x140 km and reaching a maximum of 3 cm along the shores of the lake.
The mass balance in the area is somewhat complicated. The subsiding region includes the Svartisen glacier, which is currently decreasing in mass. However, the loss of ice during 1993-1999 was three times smaller than the volume increase in the reservoir. The volume of water in the reservoir varies annually by up to 500 Mm³.
We present a detailed comparison of the filling of the dam, resulting subsidence, and the seismicity in the region and discuss implications for triggered seismicity and stress changes due to the load of the water.
[Authors] [ Overview programme] [ Keywords]
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Paper 463 - Session title: Poster Session 1
Tuesday-114 - Surface velocity flucutations and dynamics of glaciers in the Gangotri region
Satyabala, Sripati Panditaradhyula National Geophysical Research Institute, Hyderabad, India
Show abstract
We present analysis of fluctuations in the surface velocity of glaciers around the Gangotri glacier. We use ERS-SAR, ENVISAT-ASAR, ALOS-PALSAR and SENTINEL-1 to measure surface velocities during 1992-2016, an interval spanning nearly two and half decades. The glaciers studied include some tributaries of the Gangotri glacier such as the Chaturangi, Raktavarn, Kirti, etc., as well as other glaciers such as the Satopanth and Bhagirathi-Kharak glaciers which originate on the other side of Chaukhamba massif,where the Gangotri glacier originates. Some of them exhibit summer-speed up and some do not. We will investigate the implications of these studies for the dynamics of these glaciers as well as their relationship if any with the earlier findings of inter and intra-annual surface velocity fluctuations of the Gangotri glacier (Satyabala, 2016), the largest glacier in this region. Together these results shed light on the spatiotemporal dynamics of the coupled glacier system in the region.
Satyabala S.P. (2016), Spatiotemporal Variations in Surface Velocity of the Gangotri Glacier, Garhwal Himalaya, India: Study using Synthetic Aperture Radar Data, Remote Sensing of Environment, Volume 181, August 2016, Pages 151-161. http://dx.doi.org/10.1016/j.rse.2016.03.042
[Authors] [ Overview programme] [ Keywords]
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Paper 466 - Session title: Poster Session 1
Tuesday-156 - Central Italy earthquakes occurred on 2016 mapped from Space using Sentinel-1 data and open source tools.
Delgado Blasco, Jose Manuel; Cuccu, Roberto; Arcorace, Mauro; Sabatino, Giovanni; Rivolta, Giancarlo Progressive Systems Srl, Parco Scientifico di Tor Vergata, 00133, Rome, Italy
Show abstract
During 2016, Italy suffered several earthquake events with Mw ≈ 6 or higher, which caused many casualties and material damages.
In this work, Progressive Systems evaluates the occurred ground deformation using open source Earth Observation tools such as the Sentinel Application Platform (SNAP) to produce deformation maps that are in agreement with the ones already produced by the Italian authorities in this field.
We have processed Sentinel-1 data in ascending and descending tracks for the events of August and October 2016. With these results it is possible to map both extension and magnitude of the ground deformation caused by the earthquake. This information is useful not only for the general public to know and learn about these phenomena, but also for the authorities and insurance companies to estimate the potential derived damages.
Progressive Systems promotes and supports the exploitation of remotely sensed Earth Observation data and the large-scale use of higher level information retrievable by processing such data via free and open source software.
[Authors] [ Overview programme] [ Keywords]
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Paper 468 - Session title: Poster Session 1
Tuesday-43 - The Pseudo-3D Coseismic Displacement of Meinong Earthquake and Long Term Surface Deformation in Southwestern Taiwan
Yen, Jiun-Yee (1); Wang, Chun-Chin (1); Lu, Chih-Heng (2); Chang, Chung-Pai (3) 1: National Dong Hwa University, Taiwan; 2: Graduate Institute of Applied Geology, National Central University, Taiwan; 3: Center for Space and Remote Sensing Research, National Central University, Taiwan
Show abstract
On February 6, 2016, an earthquake with ML 6.4 struck southwestern Taiwan near the Meinong district of Kaohsiung, at a depth of 16.7km. The epicenter of Meinong earthquake was located near the Wutai earthquake with ML 6.1 happened in February of 2012 and the Jiashian earthquake with ML 6.4 happened in March of 2010; In addition, the focal mechanism of these three events are similar. However, aside from the aforementioned earthquakes, this area was relatively quiescent in seismicity compared to other area in Taiwan. In this study, we aim to measure the long term surface deformation and coseismic displacement of Meinong earthquake in southwestern Taiwan by processing the spaceborne radar interferometry data in the hope to reveal more deformation trend in this area.
We use 23 Envisat descending images acquired from 2004 to 2008 and 15 ALOS ascending images acquired from 2007 to 2011 processed by PSInSAR technique to observe long term surface deformation. To observe coseismic displacement, we use Sentinel-1A descending, Sentinel-1A ascending and ALOS-2 ascending images acquired before and after 6 February 2016 and processed by DInSAR technique. The results from three satellites reveal that a significant shortening displacement up to 80 mm has been noticed in Guanmiao area. Whereas an elongation up to -80mm was noticed in Meinong area. The trend was consistent with GPS observation.
We also integrated GPS and PSInSAR measurements to resolve a pseudo-3D coseismic displacement across the study area. The result shows that a significant uplift in the Guanmiao area; however, the Meinong area which is close to the epicenter reveals subsidence. For the horizontal direction, the Guanmiao area shows a significant westward motion in this event.
[Authors] [ Overview programme] [ Keywords]
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Paper 473 - Session title: Poster Session 1
Tuesday-75 - Global Estimation And Correction Approach Of Orbital Fringes
Mahmoudi, Mohamed Tadj-Eddine; Belhadj aissa, Aichouche USTHB, Algeria
Show abstract
The estimation of the Orbital Fringes (OF) by the Fourier Transform (FT) is an efficient method used generally for small and flattened area. It is known that the OF frequency and orientation changes across the scene. In fact, the FT result is the most influent frequency in the processed scene. Consequently, the FT method is not suitable for a whole scene processing.
In contrast to the FT method, that estimates the fringe frequency in the range and azimuth direction for the global scene. We propose in this paper, a novel approach to estimate the characteristics of the OF locally and to apply the correction to the whole scene.
In a brut interferogram and in a flat terrain, we can observe that the fringes are mostly in the range direction with a slight angle witch can be interpreted as the azimuthal frequency. This latter has a steady value over the scene. The phase value changes very slightly that the FT does not detect it in the azimuth direction. Even if we expand the processed window, FT will detects the fringes with inaccuracy. To overcome this problem, we propose to use the Radon Transform (RT) in order to estimate the orientation of the fringes. Consequently we can accurately synthetize the OF by using the frequency in range direction and the fringes angle to correct the brut interferogram.
Our approach was tested on a tandem acquisition of ERS 1/2 over the Algiers area. The processed zone cover rough and flat terrain, which lead us to detect and isolate the flat areas. We were able to do this by exploiting the frequency image. The second step consist to apply the correction to the whole scene. The correction uses the OF characteristics estimated in the first step of the processing.
[Authors] [ Overview programme] [ Keywords]
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Paper 479 - Session title: Poster Session 1
Tuesday-44 - Creeping behavior of El Pilar Fault is persistent over time?
Pousse, Lea (1); Jouanne, François (1); Pathier, Erwan (1); Reinoza, Carlos (2); Audemard, Franck (2); Doin, Marie-Pierre (1) 1: Isterre, France; 2: Funvisis, Venezuela
Show abstract
Northern Venezuela is crosscut by a plate boundary between the Caribbean and South America. Considering the South American plate fixed, the Caribbean plate moves 2 cm/yr to the east (DeMets et al., 2010). The major fault in the eastern part of the plate boundary is the E-W El Pilar Fault which accommodates the major part of the relative displacement between the two plates (Audemard and Audemard, 2002; Jouanne et al., 2011). Along the El Pilar Fault, each fault segment has been ruptured once or, at most, twice in the last five centuries (Audemard, 2014).
The last event was in 1997, an Ms 6.8 earthquake characterised by an important afterslip (Audemard 2006, Jouanne et al 2011). First results using GPS data measured in 2003, 2005 and 2013 on the fault underline the existence of an important creep along the fault; where ~ 40% of displacement is locked (Jouanne et al., 2011; Reinoza et al., 2015). In some case, it appears difficult to distinguish between long term creep and long term afterslip that occurs after an earthquake and decreases during the months or years following the shock. However, the identification of long term creep is essential because such phenomenon has to be taken into account in the seismic hazard assessment. In addition, identification of asperities along the faults may be a good indicator of future rupture nucleations and locations.
InSAR analysis on ALOS-1 images spanning the 2007–2011 period confirmed the presence of creep along the El Pilar fault (Pousse et al., 2016). During this period, InSAR observations show spatial variation on aseismic slip rate and also show significant temporal creep rate variations (accelerations). Locally, creep rates were higher than the relative plate motions which strongly suggest that it is a transient phenomenon. The transient behavior of the creep is not consistent with typical postseismic afterslip following the last event in 1997. The creep is interpreted as persistent aseismic slip during an interseismic period, which has a transient-like behavior. However, the durability of the creeping behavior has to be confirmed by new geodetic monitoring. We thus present a new InSAR analysis on ALOS-2 images and slip distribution inversion to show the heterogeneity of the interseismic aseismic slip in the seismogenic layer. We will thus complete the INSAR time series to detect eventual creep bursts along the fault.
[Authors] [ Overview programme] [ Keywords]
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Paper 480 - Session title: Poster Session 1
Tuesday-127 - Contribution of DInSAR technique to monitor petroleum fields
Smail, Tayeb (1); Canaslan Çomut, Fatma (2); Abed, Mohamed (1); Lazecky, Milan (3) 1: Blida UNIVERSITY, Algeria; 2: Disaster & Emergency Directorate of Denizli; 3: IT4Innovations, VSB-TU Ostrava
Show abstract
The vertical deformation of surface at In Salah Gas field is caused in part by the injection of CO2 and the production of Gas, The CO2 storage project has been in operation since 2004 with three horizontal wells into the water leg of the Krechba Carboniferous Sandstone gas producing with a reservoir thickness of 20m and 1900 meters of depth. the amount of CO2 injected at the end of 2008 was 2.5 million tonnes. Its effects is clearly visible and it is produce a deformation signature at the Earth’s surface.
This analyses use ENVISAT data to estimate land uplift and subsidence. and by using DInSAR method to investigates how CO2 injection propagate into the reservoir gives us a clear description about the direction and zones of deformation at depth.
The swelling is observed in regions surrounding the three horizontal injection wells from the wellhead to the tail, and images confirmed that the propagation is perpendicular to the well's drilling directions.
The analysis of the deformation series has revealed that The surface heave rate up to 8 to 14 mm/year was detected around all of the three injection wells . And a slightly subsidence was detected around the producers wells and it appears to be constant. This is a preliminary results and study area will be monitor with PS.
[Authors] [ Overview programme] [ Keywords]
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Paper 482 - Session title: Poster Session 1
Tuesday-90 - The SBAS Sentinel-1 Surveillance service for systematic generation of Earth surface displacement within the GEP: characteristics and first results
Casu, Francesco; Zinno, Ivana; De Luca, Claudio; Manunta, Michele; Lanari, Riccardo CNR-IREA, Italy
Show abstract
The Geohazards Exploitation Platform (GEP) [1] is an ESA originated R&D activity of the EO ground segment to demonstrate the benefit of new technologies for large scale processing of EO data. GEP aims at providing on-demand processing services for specific user needs as well as systematic processing services to address the need of the geohazards community for common information layers and, finally, to integrate newly developed processors for scientists and other expert users.
In this context, a crucial role is played by the recently launched Sentinel-1 (S1) constellation that, with its global acquisition policy, has literally flooded the scientific community with a huge amount of data acquired over large part of the Earth on a regular basis (down to 6-days with both Sentinel-1A and 1B passes). The Sentinel-1 data, as part of the European Copernicus program, are openly and freely accessible, thus fostering their use for the development of automated and systematic tools for Earth surface monitoring. In particular, due to their specific SAR Interferometry (InSAR) design, Sentinel-1 satellites can be exploited to build up operational services for the easy and rapid generation of advanced interferometric products that can be very useful within risk management and natural hazard monitoring scenarios.
Accordingly, in this work we present the activities carried out for the development, integration, and deployment of the SBAS Sentinel-1 Surveillance service of CNR-IREA within the GEP framework. The service consists on the systematic and automatic processing of Sentinel-1 data on selected Areas of Interest (AoI) to generate updated surface displacement time series via the SBAS-InSAR algorithm [2].
We built up a system that is automatically triggered by every new Sentinel-1 acquisition over the AoI, once it is available on the S1 catalogue. Then, tacking benefit from the SBAS results generated by previous runs of the service, the system processes the new acquisitions only, thus saving storage space and computing time and finally generating an updated SBAS time series.
The processing relies on the Parallel version of the SBAS (P-SBAS) [3] chain that fully benefit from distributed computing infrastructures (e.g., cloud), by making use of both multi-core and multi-node programming techniques, and allows us to effectively perform massive, systematic and automatic analysis of S1 SAR data. Moreover, innovative algorithmic, processing and storage solutions have been implemented to allow us to reduce the computing time and the required disk space. The same P-SBAS processor underlying the Surveillance service is also already available (see Figure 1) for on-demand processing through the GEP, thus allowing users to generate S1 SBAS time series on areas not covered by the service itself.
It is worth noting that the SBAS Sentinel-1 Surveillance service represents the core of the EPOSAR service, which will deliver S1 displacement time series of Earth surface on a regular basis for the European Plate Observing System (EPOS) Research Infrastructure community.
First results achieved on Neapolitan Volcanoes (Vesuvius and Campi Flegrei) and Mt. Etna will be shown at the workshop.
Acknowledgments
This work has been supported by the Italian Department of Civil Protection, the European Union Horizon 2020 research and innovation programme under the EPOS-IP project (grant agreement No. 676564), the ESA GEP (Geohazards Exploitation Platform) and I-AMICA (Infrastructure of High Technology for Environmental and Climate Monitoring - PONa3_00363) projects. Sentinel-1 data are copyright of Copernicus (2016).
References
1. https://geohazards-tep.eo.esa.int/
2. Berardino, P., Fornaro, G., Lanari, R., Sansosti, E., “A new Algorithm for Surface Deformation Monitoring based on Small Baseline Differential SAR Interferograms”, IEEE Trans. Geo. Rem. Sens., 40, 11, pp. 2375-2383, 2002.
3. F. Casu, S. Elefante, P. Imperatore, I. Zinno, M. Manunta, C. D. Luca, and R. Lanari, “SBAS-DInSAR Parallel Processing for Deformation Time-Series Computation,” Selected Topics in Applied Earth Observations and Remote Sensing, IEEE Journal, 2014.
[Authors] [ Overview programme] [ Keywords]
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Paper 485 - Session title: Poster Session 1
Tuesday-47 - Coseismic Displacement Mapping by Multi-Temporal Radar Interferometry
Zhang, Lei (1); Wu, Songbo (1); Wen, Yangmao (2); Hsu, Ya-Ju (3) 1: The Hong Kong Polytechnic University, Hong Kong S.A.R. (China); 2: School of Geodesy and Geomatics, Wuhan University; 3: Institute of Earth Sciences, Academia Sinica
Show abstract
Nowadays increasingly available radar data (especially after the launch of Sentinel-1A/B by ESA in 2014 and 2016 respectively) that cover most subaerial areas over the world are routinely being processed for mapping coseismic displacements. Conventional InSAR technique that only includes one or two image pairs in the processing chain however cannot hold a considerate promise for accurate retrieval of coseismic deformation. In the real applications, It is not rare to come across phase unwrapping errors (due to heavy signal decorrelation), topographic residuals (especially in mountainous areas), orbit errors (when using ALOS/PALSAR or Radarsat data), and atmospheric delay (in humid environments) in an InSAR derived coseismic displacement map. The unwanted signals can distort the slip inversion especially for earthquakes with moderate magnitude.
Of interest here is to develop an advanced multi-temporal InSAR (MTInSAR) framework and related processing procedures to accurately retrieve coseismic displacements from a set of radar images (rather than one or two image pairs) and therefore improve the accuracy of slip inversion. In the proposed framework we firstly estimate the topographic residuals from pre-seismic inteferograms and then design a joint model to link the topography corrected phases and parameters, i.e., the orbit error, stratified atmospheric delay and seismic displacements (including pre-, co-, and post-seismic displacements). Iterative estimation is applied to handle the magnitude discrepancy among seismic displacements. Once seismic deformation time series is obtained, principal component analysis (PCA) is conducted to mitigate the turbulent atmospheric delay. To validate the performance of the proposed methods, 2008 Mw6.3 Daxiong earthquake, Tibet and 2016 Mw6.4 Meinong earthquake, Taiwan are selected as testing events.
[Authors] [ Overview programme] [ Keywords]
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Paper 494 - Session title: Poster Session 1
Tuesday-105 - InSAR Methods in a Model- and Remote Sensing-based Toolkit for Glacier-related Natural Hazards
Loibl, David (1); Bookhagen, Bodo (2); Schneider, Christoph (1) 1: Humboldt-Universität zu Berlin, Germany; 2: University of Potsdam, Germany
Show abstract
Glacier-related hazards pose sever threats to communities in high mountain environments and adjacent regions. Started in December 2016, our joint interdisciplinary project ‘MORSANAT’ aims to create a MOdel- and Remote Sensing-based toolkit to Analyze such glacier-related NATural hazards. Study site is the Tien Shan in central Asia, an approximately E–W-orineted mountain range spanning for ~2500 km and providing a variety of heterogeneous topographic as well climatic regimes. In order to facilitate continued application, the project has a strong focus on open and freely available data and software. Within the MORSANAT toolkit, Interferometric Synthetic Aperture Radar (InSAR) techniques are of particular relevance owing to their singular capabilities to detect changes on different spatial and temporal scales. The InSAR-related method components focus on glacier motion/surges, surface elevation changes, and instable moraine as well as thaw-related landslides. Preliminary results highlight the versatility of InSAR in each of these contexts. In particular, Sentinel1 data exhibits high potential to investigate glacier-related hazards on a regional scale owing to short revisit times and adequate resolution. Subsequent to identification of critical configurations, detailed assessments will exploit the high spatial resolution of TSX and TDX data. Conversely, efficient data selection, collection and storage as well as batch processing and automatization are current challenges. We use the Python programming language to automatize processing workflows for InSAR and offset tracking. A variety of freely available software tools including ESA’s SNAP is currently being assessed regarding their potential for such automatization and overall performance in a parallel computing environment. Within the MORSANAT framework, InSAR-based results will finally be combined with insights from ground observations, glacier modeling, DEM-based spatial analysis, and optical as well as passive microwave remote sensing to facilitate an integrated analysis.
[Authors] [ Overview programme] [ Keywords]
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Paper 495 - Session title: Poster Session 1
Tuesday-67 - Mapping Land Cover and Forest Properties using Sentinel-1 Interferometry
Arsalan-Ul-Haque, Muhammad (1); Antropov, Oleg (1,2); Praks, Jaan (1) 1: Aalto University, Finland; 2: VTT, Finland
Show abstract
Synthetic Aperture Radar is an active imaging technique, not hampered by cloud cover or absence of daylight, which can be a successfully utilized for land cover monitoring in distant areas or quick registration of land cover changes. In the framework of the Copernicus programme of EU, the ESA Sentinel-1 program provides C-band SAR data in several acquisition modes with a temporal revisit time of up to 12 days (and up to 6 days since Sentinel-1B launch). The data are acquired in stripmap, interferometric wide-swath (IW), extra wide swath (EW) and wave mode (WV). Over land areas, the default acquisition option is IW mode, providing 250 km swath composed of three sub-swaths at 5 m by 20 m spatial resolution in single look. It relies on a novel type of ScanSAR technique, called Terrain Observation with Progressive Scan (TOPS) SAR, which is shrinking the azimuth antenna pattern along track direction.
Several studies (4; 5) have investigated Interferometric SAR capabilities of previous generations of satellite sensors for land cover mapping. However, the potential was relatively limited, evidenced primarily by very short tandem campaigns, or demonstrating modest accuracy figures in multi-class land-cover mapping experiments.
In this situation, appealing strategy is to consider multitemporal behaviour of InSAR coherence (4; 5; 8) to improve performance compared to single InSAR pairs. Another promising technique is fusion of SAR backscatter and InSAR coherence data which is expected to improve over results from exclusive InSAR based mapping or Sentinel-1 backscatter alone (6). Also identification of best suitable seasonal conditions (snow-covered, frozen or summer scenes) for delineating land cover classes and forest parameter inversion is important.
In this study, we analyze suitability of Sentinel-1 InSAR data for land cover and forest mapping using our test sites. Also potential of Sentinel-1 data for forest parameter retrieval is examined using set of recently proposed simple InSAR coherence models (1; 2).
The primary study area is located in southern Estonia. Its size is 12 km by 15 km and it includes Soomaa National Park in southwestern Estonia (centre coordinates 5824 N, 256E). The Soomaa site is situated on a flat terrain (elevations ranging from 20–30 m above sea level) between large mires and rivers. Reference data are represented by Estonian CORINE land cover database and optical satellite VHR data. Forest reference data are represented by airborne laser scanning measurements over Soomaa test site and stand-wise forest inventory data.
Our preliminary results indicate that some coherence pairs exhibit sensitivity towards retrieval of forest parameters in suitable geometric configuration. Potential for land cover mapping with 12-days repeat pass data is confirmed and is expected to further improve with shorter temporal baseline. Potential for SAR and InSAR model based (7) fusion (originating from water cloud model) is evaluated as well.
Further work should be aimed towards establishing new and robust ways of processing multitemporal Sentinel-1 InSAR coherence stacks as noted as well in (3)
Final results are presented at the conference.
REFERENCES
[1] A. Olesk, J. Praks, O. Antropov, K. Zalite, T. Arum ̈ae ja K. Voormansik. Interferometric SAR Coherence Models for Characterization of Hemiboreal Forests Using TanDEM-X Data. Remote Sensing 8.9 (2016), p. 700.
[2] J. Praks, A. Olesk, K. Voormansik, O. Antropov, K. Zalite ja M. Noorma. Building Blocks for Semi-empirical Models for Forest Parameter Extraction from Interferometric X-band SAR Images. IGARSS 2016, July 10-15, 2016, Beijing, China. 2016.
[3] O. Cartus, U. Wegm ̈uller, M. Santoro, C. Werner. Processing and Exploration of 12-Day Repeat-Pass Coherence from Dual-Polarization Sentinel-1 C-Band Data. EARSEL Conference 2016, June 2016.
[4] M.E. Engdahl, J. Pulliainen, and M. Hallikainen. Segment-based stem volume retrieval in boreal forests using multitemporal ERS-1/2 InSAR data. Canadian Journal of Remote Sensing 34.1-2 (2008) pp.46-55.
[5] M. E. Engdahl and J. M. Hyyppa. Land-cover classification using multitemporal ERS-1/2 InSAR data. IEEE Transactions on Geoscience and Remote Sensing 41.7 (2003) pp. 1620-1628
[6] H. Balzter, B. Cole, C. Thiel, and C. Schmullius. Mapping CORINE Land Cover from Sentinel-1A SAR and SRTM Digital Elevation Model Data using Random Forests. Remote Sensing 7.11 (2015) pp. 14876
[7] M. Santoro, J. Askne, G. Smith, J.E.S. Fransson. Stem volume retrieval in boreal forests from ERS-1/2 interferometry. Remote Sensing of Environment. 81.1 (2002) pp. 19-35.
[8] K. Zalite, O. Antropov, J. Praks, K. Voormansik, M. Noorma. Monitoring of Agricultural Grasslands with Time Series of X-Band Repeat-Pass Interferometric SAR. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 9.8 (2016), pp. 3687-3697
[Authors] [ Overview programme] [ Keywords]
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Paper 496 - Session title: Poster Session 1
Tuesday-45 - Glacier Isostatic Rebound in Central Norway Measured Using ERS-1/2 InSAR
Lauknes, Tom Rune (1); Rouyet, Line (1); Larsen, Yngvar (1); Pascal Kierulf, Halfdan (2) 1: Norut, Norway; 2: Norwegian Mapping Authority, Norway
Show abstract
Fennoscandia has been subject to major uplift in postglacial time. Along the coast in Western Norway, the deformation reflects a glacial isostatic rebound overprinted by neotectonic activity. To map and understand the complex effects, modelling and interpolated punctual in situ measurements are traditionally used.
By using long time series of ERS-1/-2 images (1993–2000) from two tracks along the Helgeland coast, and averaging (stacking) high-quality interferograms, a clear east-west trend has been measured. It shows relative differences around 5 mm (vertical) along 120 km cross-range profiles. The trend fits overall with the known uplift values and the results of the two datasets in the overlapping zone show a good match.
The results show the potential of InSAR to complement the information about crustal deformation at large scale and the value of long SAR time series for low deformation rates detection.
[Authors] [ Overview programme] [ Keywords]
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Paper 510 - Session title: Poster Session 1
Tuesday-15 - Diff-Tomo Analyses of Long- and Short-term Decorrelation of Forest Layers
Lombardini, Fabrizio University of Pisa, CNIT - Italy
Show abstract
In the developments of 3D forest Tomography, the issue of large scale and detailed characterizations of temporal decorrelation phenomena has emerged for the future spaceborne forest monitoring missions. In particular, stratified behaviour of long-term temporal decorrelation mechanisms has been analyzed by 4D (3D+Time) Differential SAR Tomography (Diff-Tomo) processing applied to large scale airborne data, and dedicated radar-tower campaigns have been conducted.
In this communication, after recalling the long-term decorrelation airborne Diff-Tomo analyses and the related robust 3D Tomography capabilities of 4D Diff-Tomo processing, developed at University of Pisa, that may be useful in the context of a second phase of the BIOMASS mission, advanced Diff-Tomo analyses exploiting a very quick acquisition ground-based array miniradar are presented. These develop investigations of both height- and time-varying characteristics of the short-term decorrelation mechanisms of the moving volumetric scatterers of windblown trees.
In particular, both height-varying short-term coherence decay time and short-term coherence level measurements are reported. This innovative characterization methodology and the new findings can be useful for the development of advanced spaceborne Tomography systems, based on tandem acquisition and 3D correlative processing, like SAOCOM-CS, for which first short-term coherence related indications are also derived.
[Authors] [ Overview programme] [ Keywords]
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Paper 511 - Session title: Poster Session 1
Tuesday-153 - Earthquake-induced Landslides Mapping By Combined Analyses Of Satellite DInSAR And Optical Data: The 24th August, 2016 Amatrice Earthquake (Italy).
Antonielli, Benedetta (2); Bozzano, Francesca (1,2); Caporossi, Paolo (1); Mazzanti, Paolo (1,2); Moretto, Serena (1); Robiati, Carlo (2) 1: Dipartimento di Scienze della Terra, “Sapienza” Università di Roma, P.le Aldo Moro 5, 00185 Rome, Italy.; 2: NHAZCA S.r.l., spin-off “Sapienza” Università di Roma, Via Cori snc, 00177 Rome, Italy.
Show abstract
On the 24th August, 2016 Central Italy was struck by a Mw 6.0 earthquake with an epicentral area near the city of Amatrice. Several landslides were triggered by the shaking in an area circa 30km in radius from the epicentral area (http://www.ceri.uniroma1.it/index.php/web-gis/cedit/). Aiming at support the detection and mapping of earthqhake-induced landslides, Satellite DInSAR technique (Differential Synthetic Aperture Radar Interferometry) combined with satellite and aerial high resolution optical imagery was used. Specifically, Sentinel-1, COSMO-SkyMed and ALOS-2 (both ascending and descending) co-seismic differential interferograms were used in combination with optical datasets available through the Copernicus Emergency Management Service.
Interferograms have been analysed firstly with un-supervised analyses, based on the detection of the fringes anomalies, i.e. particular patterns of the interferometric phase such as: i) irregular shaped fringes, ii) abrupt interruptions of the of regional co-seismic fringes, iii) localized changes in the fringes gradient.
Then, fringes anomalies have been analysed in order to detect landslide-candidates according to the following criteria: i) fringes anomalies must be located in slope areas; ii) the mean coherence values of the fringes anomalies must behigher than a predefined threshold; iii) fringes anomalies are present in more than one interferogram.
Finally, the landslide-candidates have been validated by a combined expert analysis with satellite and aerial optical images and field evidences included in the catalogue of Earthquake-induced ground failures in Italy (CEDIT).
By combining Optical and SAR images, more than 60 landslides were detected, 8 of which recognized only thanks to fringes anomalies. As a matter of fact, slopes affected by small plastic deformations (from mm to cm order) cannot be recognized by the interpretation of optical images that, on the other hand, are the only ones able to detect small scale slope failures such as rockfalls.
Further steps in this study will be the intergration of remotely sensed landslides in the catalogue of Earthquake-induced ground failures in Italy (CEDIT) and the analyses of the data available from the earthquakes occurred in Central Italy in October 2016.
[Authors] [ Overview programme] [ Keywords]
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Paper 516 - Session title: Poster Session 1
Tuesday-120 - An Advancement Of K-SVD Technique For Interferometric SAR Phase Denoising Based On Proximity Approach
Fusco, Adele (1); Ojha, Chandrakanta (2); Pinto, Innocenzo Mario (3) 1: CNR-IREA, Napoli, Italy; 2: Arizona State University, United States of America; 3: University of Sannio, Benevento, Italy
Show abstract
Synthetic Aperture Radar Interferometric (InSAR) technique widely used for analyzing geophysical monitoring of various natural phenomena on Earth, in particular monitoring subsidence and structural stability on Earth surface. Such technique has been accomplished by using an interferogram obtained by considering either two coherent SAR images from two passes of a single SAR antenna (repeat pass interferometry) or with the single pass of two-antenna system (single pass interferometry). However, multiple decorrelation effects (such as orbital errors, thermal noise, atmospheric artifacts, system errors, geometrical decorrelation etc.,) associated with an interferogram significantly affects while estimating the accuracy of results. Although, various techniques have been developed for SAR interferogram filtering, but we implemented here an advance sparsity based technique relying on sparse and redundant representations over a training dictionary. In this context, we performed an advancement of a well-known K-SVD technique based on proximity based Bayesian learning approach for interferogram phase denoising. Idea is to choose proximity based K-SVD algorithm as a signal representation technique, assuming the spatially distributed adjacent pixels have closest signal properties, which competently separates out signal from noise by means of suitable elementary signals named ‘atoms’ organized in a systematic matrix form named ‘dictionary’. We implemented this strategy on both synthetic as well as real interferometric data examining three different initial dictionaries i.e. random dictionary, dictionary using discrete cosine transform and dictionary obtain from original data. Original noise interferometric phase image is considered as the prior information, which undergoes by an iterative process of dictionary learning for phase denoising. In order to successfully validate such approach, we performed series of experiments on different interferometric data pairs of various SAR sensors with large and small spatio-temporal baseline. Hence, we select different interferograms starting from low resolution C-band ERS/ENIVSAT to medium L-band ALOS and high resolution X-band COSMO-SkyMed, over an area of Mt. Etna, Italy. From the outcome of experimental analysis, significant improvements of the noise reduction have been noticed on the interferometric phase without any considerable loss of the fringe pattern and local features as well. It is also important to highlight that the approach can be suitable regardless of the types of noise effects and interferometric baselines.
[Authors] [ Overview programme] [ Keywords]
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Paper 521 - Session title: Poster Session 1
Tuesday-128 - Doris 5 and Event-Triggered InSAR Processing
Levelt, David; Mulder, Gert; van Leijen, Freek; Hanssen, Ramon Delft University of Technology, Netherlands, The
Show abstract
The Delft Object-Oriented Radar Interferometric Software (Doris) was developed
in the late 1990s as one of the first open-source platforms for creating
interferograms from single-look complex radar images. As such it
has served the geodetic and geophysical community for almost two decades, and
formed the backbone of several time series processing chains, such as StaMPS and DePSI.
Both the advent of the Sentinel-1 mission, with its high-level coregistration
requirements, as well as increasingly demanding requirements for the efficient
processing of large data volumes, triggered the development of a 'next
generation' implementation of Doris, now available as Doris 5.
We improved, extended and integrated various software components
to support faster and more efficient setup and execution of scientific research.
Performance improvements on stack processing of Sentinel-1 images were achieved
by implementing parallelization. Basically, throughput improvements scaling linearly with the number of cores were achieved, albeit bounded in efficiency by file-I/O bottlenecks.
Coregistration procedures for Sentinel-1 are now by default based on DEM-based
coregistration (which became available in Doris 4). Millipixel coregistration
accuracy in azimuth direction is achieved by implementation of Enhanced Spectral
Diversity, and the de-ramping and re-ramping of the azimuth spectrum.
Other new elements include the burst concatenation and swath mosaicking for
adjacent sub-swaths.
Doris 5 is compatible with all the other SAR sensors used for interferometry,
such as RadarSAT-2, TerraSAR-X, Cosmo-Skymed, ALOS-2, ENVISAT and ERS-1/2.
To facilitate the automatic and autonomous interferogram generation in case of
specific events, we developed ETIP (event-triggered interferometric processing).
ETIP is currently triggered by major on-shore earthquake events, satisfying
user-defined boundary conditions. For example, the USGS earthquake webservice is used as trigger, starting an automatic processing chain that downloads the relevant Sentinel-1 satellite data, producing the interferograms, and posting these on-line for further analysis.
In our contribution, we will present the implementation and functionality of Doris 5, and show results of the ETIP chain based on Sentinel-1 data.
Doris 5 is posted on-line on http://doris.tudelft.nl and freely available for the
scientific community.
[Authors] [ Overview programme] [ Keywords]
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Paper 522 - Session title: Poster Session 1
Tuesday-154 - Damage Proxy Maps of the 2016 Central Italy Earthquake Sequence Derived from COSMO-SkyMed and ALOS-2 SAR Data
Yun, Sang-Ho (1); Liang, Cunren (1); Webb, Frank (1); Simons, Mark (2); Manipon, Gerald (1); Dang, Lan (1); Fielding, Eric (1); Gurrola, Eric (1); Agram, Piyush (1); Hua, Hook (1); Owen, Susan (1); Diaz, Ernesto (1); Milillo, Pietro (1); Rosen, Paul (1) 1: NASA - JPL, United States of America; 2: California Institute of Technology
Show abstract
The recent sequence of powerful earthquakes in the Central Italy claimed more than 300 people’s lives. In response to those earthquakes, we rapidly produced and delivered building damage maps derived from SAR observations. The M6.2 August 24, 2016 Amatrice earthquake has caused significant damage in the historic town of Amatrice, Italy. We produced damage proxy maps (DPMs) using COSMO-SkyMed and ALOS-2 SAR Data. Red pixels represent areas of potential damage due to the earthquakes as well as ground surface change during the time span of interferometric pairs. The color variation from yellow to red indicates increasingly more significant ground surface change. Preliminary validation was carried out by comparing with high-resolution pre- and post-event optical imagery acquired by DigitalGlobe's WorldView satellites, and a damage map produced by the European Commission Copernicus Emergency Management Service based upon visual inspection of high-resolution pre- and post-event optical imagery. The DPM from ALOS-2 (L-band) data covered 65-by-120 km from two consecutive frames (cyan rectangle), and the DPM from COSMO-SkyMed (X-band) data covered 40-by-50 km (red rectangle). Both DPMs cover Amatrice, revealing severe damage on the western side of the town (right panels). The time span of the data for the change is Jan. 27, 2016 to Aug. 24, 2016 for ALOS-2 and Aug. 20, 2016 to Aug. 28, 2016 for COSMO-SkyMed. Each pixel in the damage proxy map is about 30 m across. We also produced a DPM of the M6.6 October 30 Norica earthquake using COSMO-SkyMed Spotlight SAR data with pixel spacing of about 5 m and covering an area of 10-by-10 km, centered at Norcia, Italy. These DPMs provide broad geographic coverage of the earthquake's impact in the region in a consistent manner that may bring more robust detection compared to human visual inspection.
[Authors] [ Overview programme] [ Keywords]
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Paper 528 - Session title: Poster Session 1
Tuesday-123 - Automated Processing of Sentinel-1 InSAR Products
Hatton, Emma (1); Gonzalez-Mendez, Pablo J. (2); Spaans, Karsten (1); McDougal, Alistair (1); Walters, Richard (3); Wright, Tim (1); Hooper, Andrew (1) 1: School of Earth and Environment, University of Leeds, United Kingdom; 2: School of Environmental Sciences, University of Liverpool, United Kingdom; 3: Department of Earth Sciences, Durham University, United Kingdom
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The Sentinel-1 constellation provides unprecedented Synthetic Aperture Radar (SAR) coverage of the world. With a constellation revisit rate of up to 6 days in certain areas with most of the globe acquired at least every 24 days, the volume of data collected provides an excellent resource for scientists, however, this volume of data also presents a challenge for studying processes which occur over a large area or long time frame. In order to make the best use of the data available, automated processing systems are essential.
There are numerous challenges associated with the development of a processing system for the Sentinel-1 data including the slicing strategy employed in the L1 processing and dissemination system. When operating in Terrain Observation by Progressive Scanning (TOPS) mode, the SAR sensors collects bursts of data which are synchronised between repeat passes, however delivered scenes of the same area have not always been sliced to contain the same set of bursts. For the production of good quality Interferometric SAR (InSAR) products, identical coverage is desirable. To this end, the Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET) has developed an automated processing system, LiCSAR, which first records information about all acquired bursts in a database and rebuilds the Single Look Complex (SLC) data into predefined frames before further processing the data into wrapped interferograms and coherence images. Planned post-processing stages include the production of time series and strain maps.
Initial processing has focussed on the production of interferograms and coherence images over the Alpine Himalayan Belt, though the geographic area will be slowly expanded. Products are available for download via the COMET portal.
[Authors] [ Overview programme] [ Keywords]
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Paper 529 - Session title: Poster Session 1
Tuesday-76 - Near Real Time Ice Velocity Service
Hatton, Emma (1); Hogg, Anna (1); Muir, Alan (2); Shepherd, Andrew (1); Lemos, Adriano (1) 1: CPOM, School of Earth and Environment, University of Leeds, United Kingdom; 2: CPOM, University College London, United Kingdom
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The volume and extent of the Synthetic Aperture Radar (SAR) data collected by the Sentinel-1 platform is unprecedented. In a high-inclination orbit with a constellation repeat of 6 days, the polar coverage allows for Near Real Time monitoring of changes in the ice with SAR for the first time.
The Centre for Polar Observation and Modelling (CPOM) has been routinely processing Sentinel-1A/B data to create ice velocity products over 5 key glaciers from 2014 to the current day. Ice velocity products and transect data can be accessed through the CPOM Ice Velocity Portal, providing a near-real time service to users.
[Authors] [ Overview programme] [ Keywords]
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Paper 552 - Session title: Poster Session 1
Tuesday-144 - Monitoring Greenland ice flow from Sentinel-1 SAR data
Neckel, Niklas; Lüttig, C.; Helm, V.; Humbert, Angelika Alfred Wegener Institute, Germany
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Today, Sentinel-1 Synthetic Aperture Radar (SAR) data is routinely employed to monitor large-scale ice sheet velocities by means of intensity offset tracking. Raw velocity fields from intensity offset tracking are often disturbed by outliers from offset misregistration and need to be filtered before further interpretation and analysis. Here we show a most recent velocity mosaic of the entire Greenland ice sheet, employing a robust three step filtering strategy to exclude outliers from the raw velocity fields before stacking the data to an ice sheet wide mosaic. Velocity fields derived from intensity offset tracking might capture the large scale flow of fast moving glaciers and ice streams but get less accurate in the interior of the ice sheets where the ice moves at lower speed. Therefore, we additionally examine the onset velocity of the Northeast Greenland Ice Stream (NEGIS) by means of 6-day repeat pass Sentinel-1 SAR interferometry by combining data from ascending and descending satellite orbits. Precise knowledge of ice flow is of particular interest in this region as the East Greenland Ice-core Project (EastGRIP) is located here.
[Authors] [ Overview programme] [ Keywords]