RSIT: A waveform retracking method based on reconstructed sea surface height and iterative threshold for coastal altimetry data

Extending satellite radar altimetry measurements from the open ocean to the coastal zone can improve the accuracy and quality of monitoring coastal sea level. However, radar altimetry waveforms can be distorted by any inhomogeneity in the properties of the surface observed within the footprints, possibly leading to range measurement errors. To address these issues, a coastal retracking method based on reconstructed sea surface height and iterative threshold (RSIT) is proposed in this paper. RSIT involves several steps: First, the sea surface height components are reconstructed as prior information to compute the initial retracking gate. Next, iterate the amplitude scale factor of the entire waveform to identify possible sub-waveforms. After each iteration, continuity between neighboring sub-waveforms is assessed. Eventually, the optimal retracking gate is determined from all identified sub-waveforms. We validated RSIT using Jason-2 data in the coastal regions of Australia and Pakistan. Experimental results show that RSIT can retrieve more available altimetry data and enhance the accuracy by nearly 37.5% and 23.1% compared to ALES within the last few kilometers to the coast, respectively. Moreover, the impact of varied errors in reconstructed sea surface height on RSIT was discussed, with the results reveal that RSIT has strong robustness to errors within 1 m, making it suitable for application in most coastal zones.