Multi- Calibration and Cross Validation of Hy-2b/C/D Altimeters Using a Mobile Transponder

HY-2C (Haiyang) and HY-2D were launched on 21 September 2020 and 19 May 2021 separately, which form China’s marine dynamic satellite constellation program with HY-2B, launched on October 25, 2018. The calibration mission for HY-2B altimeter was carried out in 2019, and a precision of less than 1 cm was achieved. For further validation, a comparison between HY-2B and Jasons was performed in SSH (Sea Surface Height). To obtain consistent and comparable calibration results, a mobile transponder was utilized in different sites for HY-2B/C/D altimeters. Two experiment missions were carried out in 2021 and 2022 separately, each for a month. The result shows the range calibration precision for HY-2B/C/D is less than 4 cm, and USO (Ultra Stable Oscillator) drift on board is very small and negligible compared with HY-2A. Further, the range bias correction of the altimeter instrument is defined and will be compiled into the L1 data to improve the quality of L2 data product. In March this year, a novel calibration method is developed on offshore, with the altimeter switched to ocean calibration mode. This paper gives a detailed description of the multi-calibration of HY-2B/C/D altimeter using a mobile transponder. The results are validated with the ocean mode calibration, which shows a high consistency. In the following mission, the mobile transponder will be installed offshore on the altimeter ground track permanently, performing regular range and sigma zero calibration.