Comprehensive Results of DLR's Independent Verification of the Sentinel-1C SAR System Calibration with an Outlook for Sentinel-1D

Abstract

European Space Agency's (ESA) Sentinel-1C (S1C) is the third satellite of the Sentinel-1 mission. Launched in early December 2024, it ensures seamless continuity of C-band SAR data for global monitoring of the Earth surface in the framework of the Copernicus program. In parallel to the commissioning of S1C by ESA, an independent SAR system calibration has been performed by DLR on behalf of ESA during the first half of 2025. Based on an efficient calibration strategy, this presentation will give a detailed account of the different activities which have been carried out by DLR, culminating in our contribution to a successful in-orbit commissioning review in May 2025. Due to the stringent performance requirements of Sentinel-1, on behalf of ESA, the DLR SAR Calibration Center already performed a similarly organized independent end-to-end system calibration of S1A in 2014 and of S1B in 2016, relying on a separate dedicated suite of in-house analysis tools and the innovative and highly-stable reference ground targets deployed along DLR's SAR calibration field in Southern Germany. However, S1C is not simply an exact rebuilt of its predecessors S1A/B but has implemented a series of hardware improvements for lessons learnt with the previous missions. These novel aspects, their impact on the calibration strategy will be briefly introduced in the presentation before turning to a comprehensive discussion of the results obtained throughout the S1C commissioning phase. After a general overview of all DLR activities, this presentation will focus on our detailed assessment of all L1-based performance results, such as pointing and antenna model verification, point target evaluations and InSAR verification activities. We will show that S1C has proven to be an excellent instrument with a very stable performance which out-of-the-box exhibited only small antenna mispointing and a calibration factor very close to S1A/B. Due to this excellent early performance, our InSAR activities could not only demonstrate S1C/S1C interferometry as well as S1C/S1A cross-interferometric performance over largely stationary scenes but we could successfully derive the ground shift along the Sagaing fault induced by the Myanmar 28 March 2025 earthquake. Last but not least, the next member of the Sentinel-1 family, Sentinel-1D is currently scheduled to be launched shortly after this year's CEOS workshop in early November 2025. In the last part of this presentation, we will therefore turn to the lessons learnt from this year's S1C campaign and discuss adaptations which will be implemented for our imminent independent verification campaign for S1D.