DLR's Independent Calibration of the Sentinel-1C System - First Results from S1C Commissioning Phase Activities

Kurzfassung

European Space Agency's (ESA) Sentinel-1C (S1C) is the third satellite of the Sentinel-1 mission. To be 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 (e.g., [1]). In parallel to the commissioning of S1C by ESA, an independent system calibration is performed by DLR on behalf of ESA. Based on an efficient calibration strategy, this paper details the different activities planned and executed by DLR and presents first calibration results. 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 ([2], [3]) and of S1B in 2016 [4], 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 (e.g., [5]) 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 and their impact on the calibration strategy will first be briefly introduced in this presentation. Launch of S1C is currently foreseen for early December 2024 with the ensuing commissioning phase activities to be performed between early January and late April 2025. This will therefore allow us to then present and discuss the results achieved by the DLR team during the S1C in-orbit commissioning phase at the symposium. 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. References: [1] R. Torres, D. Geudtner, S. Lokas, D. Bibby, P. Snoeij, I. N. Traver, F. Ceba Vega, J. Poupaert, and S. Osborne, "Sentinel-1 Satellite Evolution," in IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, July 2018, pp. 1555-1558. [2] M. Schwerdt, K. Schmidt, N. Tous Ramon, G. Castellanos Alfonzo, B. J. Döring, M. Zink, and P. Prats-Iraola, "Independent Verification of the Sentinel-1A System Calibration," IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, vol. 9, no. 3, pp. 994-1007, 2016. [3] M. Schwerdt, K. Schmidt, N. Tous Ramon, G. Castellanos Alfonzo, B. Doering, M. Zink, and P. Prats, "Independent Verification of the Sentinel-1A System Calibration - First Results," in EUSAR 2014; 10th European Conference on Synthetic Aperture Radar, June 2014, pp. 1259-1262. [4] M. Schwerdt, K. Schmidt, N. Tous Ramon, P. Klenk, N. Yague-Martinez, P. Prats-Iraola, M. Zink, and D. Geudtner, "Independent System Calibration of Sentinel-1B," Remote Sensing, vol. 9, no. 6: 511, 2017. [5] M. Jirousek, B. Doering, D. Rudolf, S. Raab, and M. Schwerdt, "Development of the highly accurate DLR Kalibri Transponder," in EUSAR 2014; 10th European Conference on Synthetic Aperture Radar, June 2014, pp. 1176-1179.