A subwaveform threshold retracker for ERS-1 altimetry: A case study in the Antarctic Ocean

Based on a correlation analysis method, a subwaveform threshold retracker is developed and coded in FORTRAN for satellite altimetry to determine the leading edge and retracking gate, and to improve the precision of sea surface heights (SSHs) and gravity anomalies (GAs). Using ERS-1/ERM waveforms, the subwaveform threshold retracker outperforms full-waveform threshold retrackers at the tide gage Port Station. A direct comparison between retracked SSHs and in situ SSHs is made at tide gage Port Station. Here the subwaveform retracking improves SSH precision from 0.241 to 0.193 m, yielding an improvement percentage (IMP) of 20%. Using ERS-1/GM waveforms, the subwaveform threshold retracker outperforms the Beta-5 and full-waveform threshold retrackers over the Bellingshausen and Amundsen Seas (BAS) in the Antarctic Ocean. The standard deviations of raw and retracked SSHs are 0.157 and 0.070 and 1.836 and 0.220 m over the ice-free and ice-covered oceans, corresponding to IMPs of 54.4% and 88%, respectively. Use of retracking improves the precision of GAs by up to 46.6% when comparing altimeter-derived and shipborne GAs.