Initial Results of DLR's Independent Verification of the Sentinel-1C System Calibration

Abstract

European Space Agency's (ESA) Sentinel-1C is the third satellite of the Sentinel-1 mission. Launched in December 2024, it will ensure 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 Sentinel-1C by ESA, an independent system calibration is performed by DLR on behalf of ESA. Based on an efficient calibration strategy, this paper gives a detailed account of the different activities which have been carried out by DLR. Due to the stringent performance requirements of Sentinel-1, the DLR SAR Calibration Center already performed for ESA 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, S1-C 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 discussed in the presentation before turning to the results obtained throughout the S1-C commissioning phase. S1-C has been launched on December 5th, kicking off its commissioning phase of approximately five months duration in the first half of 2025. This will therefore allow us to present and discuss the outcome obtained by DLR in support of the S1-C in-orbit commissioning phase. After a general overview of all DLR activities, this presentation will focus on a detailed assessment of all L1-based performance results, such as pointing and antenna model verification, point target evaluations and InSAR verification activities. Last but not least, results of cross-calibration activities between Sentinel-1A and S1C acquisitions will be discussed.