摘要：The paper presents a method estimating the HY-2A altimeter ultra stable oscillator (USO) drift with a reconstructive transponder. The frequency of the USO of the in-orbit altimeter changes with age, and a bias between the actual frequency and the nominal one exists. The USO bias contributes a portion of the altimeter range drift. The HY-2A altimeter transmits signals at a fixed time interval during calibration, and the actual interval between adjacent altimeter transitions, which is controlled by the USO, is different from the nominal one due to the USO drift. The reconstructive transponder measures the arrival times of the altimeter transmitted signals accurately with the atomic clock. The drift of the USO on-board the HY-2A altimeter can be estimated accurately by using the ranges from the reconstructive transponder and the HY-2A altimeter. The USO drifts of around 40 cm/year are presented. Furthermore, the multi-mission crosscalibration provides preliminary validation of HY-2A altimeter USO drift.
摘要：This letter presents a method for matching satellite radar altimeter data and transponder data generated during in situ calibration. The transponder generates a measurement error when it measures the arrival time of the altimeter’s transmitted signal and embeds the error in both the transponder’s recorded data and the altimeter’s recorded data. The secondorder finite difference sequence of this error sequence can be extracted from the raw data, thus, the correspondence between two identical but mismatched second-order difference sequences can be uniquely established. The measurement error is utilized,and a data matching method that can uniquely establish the correspondence between the altimeter’s recorded data sequence and the transponder’s recorded data sequence is presented.This post-processing method does not increase the real-time signal processing workload of the transponder. Furthermore,The principles underlying this method can be used for any transponder that can adjust the response signal delay during calibration.