A Novel Method for Altimeters Calibration Using a Coastal Transponder

China’s marine dynamic satellite constellation was formed in 2021 with the launch of HY-2D, with existing HY-2C and HY-2B. The SSH (Sea Surace Height) calibration by tide-gauges, buoys as well as range calibration utilizing transponders have been performed extensively. In order to correlate the SSH and range calibration in one experiment, search the association between the two biases, furtherly, to compile the range bias obtained by transponders into the altimeters data products, a novel calibration method was developed utilizing a coastal transponder. In the new method, the altimeter works at normal SSH tracking mode, and the transponder captures the pulses instantaneously, transmits them back entering the altimeters receiving windows. From the altimeter spectra, the correlation between the SSH and the transponder echoes are achieved, and the two biases could be validated. In this paper, all the China’s coastal tracks of HY-2B/C/D were examined, and four sites were selected. In March and August in 2023, two calibration missions were carried out. Besides the range bias, the SSH validation was analyzed for the first time. The new method shows potentials in combing the transponder and the sea surface methods. At present, some new calibration techniques based on the signal-rebuilt transponder are in research, involving the fully-focused SAR processing and the absolute measurements of ranges and the instrument resolutions. These new methods are expected to serve for the next advanced altimeters which would be launched in a few years.