Unwrapping the phase of a single Synthetic Aperture Radar image: application to Sea Level Anomaly from Sentinel-1 satellite

Summary

We describe a method to unwrap the phase of a satellite-borne Single Look Complex (SLC) of conventional Synthetic Aperture Radar (SAR) data, classically assumed to be stochastic noise. It yields the lengthening or shortening of the optical path from a single SAR acquisition. We tested a spaceborne implementation, based on Sentinel-1 mission, over the Indian ocean. Our results seem to correspond to a geophysical signal related to the instantaneous deviations from the mean sea surface, i.e. the Sea Level Anomaly (SLA), at high spatial resolution. Only the line-of-sight component is measured by this technique. Where the signals can be colocated, we observed good agreement in comparison with SLA based on conventional Altimetry. This method might enable the use of SAR archives for coastal sea-level measurements, since 1991, a research area where observations are lacking.