Sentinel-1 In-Orbit Calibration Approach
Østergaard, A.¹; Navas-Traver, I.¹; Snoeij, P.¹; Brown, M.¹; Rommen, B.¹; Geudtner, D.¹; Bibby, D.¹; Torres, R.¹; Schied, E.²; Rostan, F.²; Schwerdt, M³; Zink, M.³; Bauleo, A⁴; Croci, R⁴; Pietropaolo, A.^4
1ESA, NETHERLANDS; ²EADS Astrium GmbH, GERMANY; ³DLR, GERMANY; ⁴Thales Alenia Space, ITALY

ESA is developing the Sentinel-1 European Radar Observatory, a constellation of two polar orbiting satellites that provide C-band SAR products for operational applications. The Sentinel-1 mission has been designed to comply with stringent radiometric stability and accuracy requirements. To ensure these requirements are achieved, the mission relies on an efficient and robust strategy for in-flight calibration. This consists of (a) pulse-coded internal calibration pulses that achieve leakage cancellation and robust estimation and separation of different types of leakage signals and (b) an Antenna Model that estimates very accurately the antenna radiation patterns based on the instrument configuration and pre-launch measurements. Usage of calibration data and the Antenna Model enables that only a graceful degradation of performance would occur throughout the instrument lifetime, even in the event of unrecoverable failures of individual transmit/receive modules. During the commissioning phase, calibration also relies on precise external calibration transponders and measurements with notch patterns over the rainforest and transponders for accurate pointing determination. This paper describes the overall strategy and the different activities required for in-flight calibration of Sentinel-1.