ESA & Sentinel-1 Session

As part of the European Copernicus programme, the Sentinel-1 mission, based on a constellation of two SAR satellites, ensures continuity for Europe of C-band SAR observations. Sentinel-1A and Sentinel-1B were respectively launched from Kourou on 3rd April 2014 and 25th April 2016.

The presentation will give an overview of the overall mission status. At the time of FRINGE 2017, it is expected that the operational qualification of the Sentinel-1 constellation (Sentinel-1A and Sentinel-1B) will be completed or close to completion, leading to the full operations capacity of the mission.

Topics including mission achievements, mission observation scenario provided by the constellation and operations performance will be presented.

 

Since the end of the Sentinel-1A satellite commissioning activities in September 2014, the mission operations have ensured the open and free on-line access to Sentinel-1 products while gradually increasing the overall mission capacity. Following the launch of Sentinel-1B in April 2016, the mission provides today an unprecedented amount of qualified  operational products to a continuously growing user community.  By December 2016,  about one million of Sentinel-1 products are available for user download, corresponding to about 1.3 PB of data. A number of changes aiming at supporting the user community and maximising the mission exploitation have been introduced in the mission operations since the start of Sentinel-1A operations in 2014, including in particular the systematic availability of Level-1 Single Look complex products for all data acquired in IW mode. The mission capacity will further increase in 2017 with the start of the EDRS-A operations for Sentinel-1A and later on with Sentinel-1B. This paper provides a summary of the mission operations since September 2014 and presents an overview of their future evolution and what will this represent from a user perspective.

In the framework of the EU/ESA co-funded Copernicus program [RD-1] (formerly known as Global Monitoring for Environment and Security -GMES). ESA is developing and operating a series of Sentinel missions with the objective to provide routinely Earth Observation data for supporting the implementation of operational Copernicus services and for existing or future national service initiatives.

Copernicus is composed by six different services organized by thematic areas being:

Copernicus Marine Environment Monitoring Service (CMEMS) encompasses monitoring for marine safety and transport, oil-spill detection, water quality, weather forecasting and the polar environment.

Copernicus Land Monitoring Service (CLMS) includes monitoring for water management, agriculture and food security, land-use change, forest monitoring, soil quality, urban planning and natural protection services.

Copernicus Atmosphere Monitoring Service (CAMS) includes monitoring for air quality and ultraviolet radiation forecasts, greenhouse gases and climate forcing.

Copernicus Emergency Management Service (EMS) helps mitigating the effects of natural and manmade disasters such as floods, forest fires and earthquakes and contributes to humanitarian aid exercises.

Copernicus service for Security applications aims to support European Union policies by providing information in response security challenges. It improves crisis prevention, preparedness and response in three key areas: border surveillance; maritime surveillances, support to EU External Action

Copernicus Climate Change Service (C3S) responds to environmental and societal challenges associated with human-induced climate changes.

Copernicus services rely on a wide space component including dedicated missions specifically designed being the Sentinels.

Sentinel-1 (S-1) state-of-the-art satellites [RD-2] are equipped with an antenna achieving beam steering with a high accuracy in both elevation and azimuth. It allows a high flexibility in SAR data acquisition, in terms of resolution and coverage. Sentinel-1 features four operational modes:

Stripmap mode: 5x5 m resolution, 80 Km swath

Interferometric Wideswath (IW) mode: 5x20 m resolution, 250 Km

Extra-Wideswath mode: 20x40 m resolution, 400 Km

Wave Mode: 5x5 m resolution, 20x20 Km imagettes

IW and EW modes are based on the Terrain Observation by Progressive Scan mode (TOPS) mode [RD-3]. TOPS feasibility has been first demonstrated by the Terrasar-X mission [RD-4] and is now for the first time used as main operational mode on a spaceborne mission with Sentinel-1.

TOPS IW being the main mode of observation over land and it supports all land applications including interferometry. Its suitability to interferometry in an operational manner has been often questioned. However, it has been demonstrated since that thanks to tight orbit control [RD-5] and to the commanding strategy, it is possible to deliver INSAR value added products with a quality beyond the expectations [RD-6][RD-7].

Stripmap (SM) is a legacy mode from ERS and ASAR. Initially, it was not supposed to be used operationally, however considering the performances achieved especially in terms of azimuth resolution comparing to TOPS, it has been decided to use it over volcanic islands respecting two conditions: fully imaged by the 80 Km swath and not interfering with other applications.

WaVe (WV) is the default mode over open oceans polarisation. Like its predecessors (ERS and ASAR) it provides a discrete scanning of the ocean surface acquiring imagettes separated each by 100Km and alternatively switching between two beams in order to optimize the sampling of the imaged swell systems. The S-1 WV mode provides wider imagettes (20x20Km), better resolute and with better performances opening the door to enhanced capacity to resolve swell system and to new retrieval approaches [RD-8].

Sentinel-1 (S-1) is a constellation of two polar orbiting satellites equipped with a C-band Synthetic Aperture Radar (C-SAR) instrument. The first satellite unit, Sentinel-1 A (S-1A), was successfully on the 3rd of April 2014 followed by the second unit two years after, Sentinel-1B (S-1B), on the 25th of April 2016. Both were launched on a Soyuz rocket from Europe’s Spaceport in French Guiana. The constellation was declared ready for operation after the successful commissioning on S-1B on the 14th of September 2016.

This paper is composed in three parts. It first gives an overview of the S-1A performance recalling the main challenges for the radiometric calibration and showing the improvement and evolution after more than two years of operations. The focus will be put on the radiometric, geometric calibration and on the main spacecraft performance indicators especially for the main TOPS modes.

In a second part it will summarizes the main results of the S-1B during and since the commissioning phase and then will present combined results from the two units to give a figure on the overall constellation. Finally it will present the progress of an activity aiming at cross-comparing the two main providers of C-band data, Sentinel-1 and Radarsat-2.

2. References

[RD- 1] http://copernicus.eu/

[RD- 2] Sentinel-1: ESA’s Radar Observatory Mission for GMES Operational Services (ESA SP-1322/1, March 2012)

[RD- 3] F. De Zan, A. Monti Guarnieri, “TOPSAR: Terrain Observation by Progressive Scans”, IEEE TGRS 2006.

[RD- 4] A. Meta, J. Mittermayer, P. Prats, R. Scheiber and U. Steinbrecher, "TOPS Imaging With TerraSAR-X: Mode Design and Performance Analysis," in IEEE Transactions on Geoscience and Remote Sensing, vol. 48, no. 2, pp. 759-769, Feb. 2010. doi: 10.1109/TGRS.2009.2026743

[RD- 5] P. Prats-Iraola et al., "Role of the Orbital Tube in Interferometric Spaceborne SAR Missions," in IEEE Geoscience and Remote Sensing Letters, vol. 12, no. 7, pp. 1486-1490, July 2015.
doi: 10.1109/LGRS.2015.2409885

[RD- 6] N. Yague-Martinez, P. Prats-Iraola and F. De Zan, "Coregistration of Interferometric Stacks of Sentinel-1A TOPS Data," Proceedings of EUSAR 2016: 11th European Conference on Synthetic Aperture Radar, Hamburg, Germany, 2016, pp. 1-6.

[RD- 7] N. Yagüe-Martínez et al., "Interferometric Processing of Sentinel-1 TOPS Data," in IEEE Transactions on Geoscience and Remote Sensing, vol. 54, no. 4, pp. 2220-2234, April 2016.
doi: 10.1109/TGRS.2015.2497902

[RD- 8] F. Ardhuin, F. Collard, B. Chapron, F Girard-Ardhuin, G. Guitton, A. Mouche, J. E. Stopa, “Estimates of ocean wave heights and attenuation in sea ice using the SAR wave mode on Sentinel‐1A”, Vol. 42, issue 7, April 2015, Pages: 2317–2325, DOI: 10.1002/2014GL062940

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