Pseudo-swath Processing of CryoSat-2 SARIn Waveforms for Inland Water

Abstract:

With the launch of CryoSat-2 (CS2) only a decade ago, inland water altimetry has come a long way. The introduction of Synthetic Aperture Radar (SAR) altimetry brought along a whole new range of monitoring possibilities of inland water bodies. With an along track resolution of around 300 m, the community was suddenly able to study rivers and lakes that were not visible with conventional Low Resolution Mode (LRM) altimeters. However, the 300 m resolution is still a challenge for the smallest water bodies, and sometimes none or only a single observation is available.

In some regions, mostly in regions with a complex topography, the CS2 altimeter operates in SAR Interferometric (SARIn) mode, using two antennas, where the phase difference between the two returns can be used to locate the across-track origin of the echo. Traditionally, retracking methods are applied to a single bin of the waveform, resulting in a single surface height estimate. In this study, we use a pseudo-swath approach where multiple peaks of single SARIn waveforms are retracked and geolocated across track using the phase difference information. By doing this, a high number of water level estimates (WLE) can be acquired for each waveform, even from water bodies that are not immediately located at the satellite ground track. We investigate the potential of this technique over rivers and lakes by looking at the increase in coverage as well as at the impact on the precision of the measurements. Increasing the number of WLE is of great importance especially for small water bodies, where the number of available valid measurements is very limited. Using a swath-like approach could also provide useful information about river topography.