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1. chinaXiv:201612.00205 [pdf]

HY-2A Radar Altimeter Ultra Stable Oscillator Drift Estimation using Reconstructive Transponder with its Validation by Multi-mission Cross-Calibration

Junzhi Wan; Wei Guo; Fei Zhao; Caiyun Wang; Peng Liu
Subjects: Geosciences >> Space Physics

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.

submitted time 2016-12-26 Hits1950Downloads657 Comment 0

2. chinaXiv:201612.00199 [pdf]

Echo Signal Quality Analysis During HY-2A Radar Altimeter Calibration Campaign Using Reconstructive Transponder

Junzhi Wan; Wei Guo; Fei Zhao; Caiyun Wang; Peng Liu; Mingsen Lin; Hailong Peng; Chuan Xu
Subjects: Geosciences >> Space Physics

A reconstructive transponder has been utilized for the in-orbit calibration campaign of the HY-2A radar altimeter since March 2012. The precision of final calibration result is influenced by echo signal's quality in the HY-2A altimeter's range window. As an indicator of the signal's quality, echo signal dwell time is analyzed considering its influence on signal quality and its uncertainty. In HY-2A altimeter calibration, the echo signal dwell time is determined by the radial orbit prediction uncertainty and the real-time signal processing mechanism of the reconstructive transponder. The real-time signal processing mechanism of the reconstructive transponder utilizes some incoming signal samples without sending echo signals before transmitting. Comparing with the length of the HY-2A altimeter's range window, the radial orbit prediction uncertainty is large. Large radial orbit prediction uncertainty and signal processing mechanism of the reconstructive transponder are two main factors that limit the echo signal dwell time in HY-2A altimeter calibration. Finally, approaches for increasing echo signal dwell time are briefly proposed.

submitted time 2016-12-26 Hits1943Downloads607 Comment 0

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