Sentinel-1 System Overview and Performance
Geudtner, Dirk; Torres, Ramón; Snoeij, Paul; Ostergaard, Allan; Navas-Traver, Ignacio; Rommen, Björn; Brown, Michael

In the framework of the EU/ESA co-funded Global Monitoring for Environment and Security (GMES) program, ESA is undertaking the development of a series of five Sentinel missions with the objective to provide routinely Earth observation data for the implementation of operational GMES and national user services. The GMES services comprise mapping and forecasting activities for Land, Marine, Atmosphere, Emergency, Security, and Climate change.

As part of the GMES space component, the Sentinel-1 (S1) mission is implemented through a constellation of two satellites (A and B units) each carrying an imaging C-band SAR instrument (5.405 GHz) providing data continuity of ERS and ENVISAT SAR types of mission. Each Sentinel-1 satellite is designed for an operations lifetime of 7 years with consumables for 12 years. The S-1 satellites will fly in a near polar, sun-synchronized (dawn-dusk) orbit at 693 km altitude.

The Sentinel-1 mission, including both S-1A and S-1B satellites, is specifically designed to acquire systematically and provide routinely data and information products for GMES Ocean, Land and Emergency services. These services focus on operational applications such as the observation of the marine environment, including oil spill detection and sea-ice monitoring, the surveillance of maritime transport zones (e.g. European and North Atlantic zones), as well as the mapping of land surfaces including vegetation cover (e.g. forest), and mapping in support of crisis situations such as natural disasters (e.g. flooding and earthquakes) and humanitarian aid.

In addition, the 12-day repeat orbit cycle of each Sentinel-1 satellite along with small orbital baselines will enable SAR interferometry (InSAR) coherent change detection applications such as the monitoring of surface deformations (e.g. subsidence due to permafrost melt) and cryosphere dynamics (e.g. glacier flow). The Sentinel-1 SAR instrument with its active phased array antenna supports four exclusive imaging modes providing different resolution and coverage: Interferometric Wide Swath (IW), Extra Wide Swath (EW), Stripmap (SM), and Wave (WV). All modes, except the WV mode can be operated in dual polarization. Both the IW and EW mode operate in TOPS (Terrain Observation with Progressive Scans in azimuth) mode [2] providing large swath width of 250 km and 400 km, respectively with enhanced image performance as compared to the conventional ScanSAR mode.

The paper provides an overview of the Sentinel-1 system characteristics including the SAR imaging modes and their key performance parameters as well as the specifics of related attitude and orbit control modes (i.e. roll steering mode and zero-Doppler steering mode). In addition, the Sentinel-1 mission capabilities, focussing especially on TOPS interferometry (InSAR) are discussed.