Advanced Bathymetry Retrieval from Swell Patterns in High-Resolution SAR Images

We present an enhanced technique to retrieve underwater topography in coastal areas from swell refraction patterns in high-resolution spaceborne synthetic aperture radar (SAR) images. From a SAR scene with swell patterns propagating shoreward, we compute the peak wavelength and wave direction of each sub-scene; we then obtain depth estimates via the linear dispersion relationship, as long as the wave period is known. Compared to previously presented depth retrieval methods based on the same principles, the innovation of our technique consists of implementing a modulation transfer function (MTF) to account for the dependence of the strength of radar signatures of ocean waves on their wavenumber and propagation direction relative to the radar look direction. We compare the SAR-derived depth maps obtained with and without the MTF-based approach and our results indicate that there is an improved accuracy in the former, statistically quantified by a higher correlation coefficient (r2=0.85 with the MTF-based approach, as opposed to r2=0.77 without it) and a lower RMSE (6.37 m with the MTF-based approach, as opposed to 8.74 m without it) with respect to the reference depths