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Abstract
This study focuses on assessing the accuracy of 20-Hz waveform retracked Jason-2 (J-2) altimetry sea surface heights (SSHs) in the vicinity of Taiwan by comparisons with the TOPEX/Poseidon (T/P) 10-Hz SSHs and sea level data from the Anping tide gauge. The study areas exhibit high, medium, and low amplitudes of ocean tides and contain diverse bathymetries with depths of 0–4000 m. The performance of Offset Center of Gravity (OCOG), threshold, modified threshold, and ice retrackers was examined by comparing the retracked SSHs with Earth Gravitational Model 2008 (EGM08) geoid via the use of the improvement percentages (IMPs). The results indicate that both altimetry measurements are significantly improved by waveform retracking techniques, with a maximum IMP of 46.6% for T/P and 82.0% for J-2, and the optimal achievement of retrackers is influenced by the characteristics of the study areas. In addition, valid retracked J-2 SSHs are much closer to shorelines than T/P. A comparison of retracked J-2 data with Anping tide gauge records reveals that applying the optimal retracking algorithms reduces the root mean squares of differences and increases the number of valid measurements.
Acknowledgements
This research is supported by grants from the National Science Council of Taiwan (NSC 97-2221-E-006-206-MY2; NSC 100–2221–E–006–233) and National Cheng Kung University. Co-author Hyongki Lee is partially supported by a grant from NASA's OSTST Program. Satellite altimetry data (GDRs and SDRs) are provided by PODAAC, JPL under a contract from NASA. We acknowledge C.K. Shum for invaluable discussions and comments on the manuscript and computational support to make this study possible. We thank anonymous reviewers for their constructive comments.