Estimation of Coastal Bathymetry Using RISAT-1 C-Band Microwave SAR Data

The study of swell wave refraction phenomena using synthetic aperture radar (SAR) data has been found to be very useful in estimating the underwater topography (seabed structure). Near-shore water regions generate a wide range of surface signatures due to rapidly changing underwater depths, which cause waves to refract and finally align parallel to the shoreline. Another significant change, which is observed as gravity waves approach the shoreline, is that their wavelength decreases and, as the energy of the wave is constant in the absence of dissipating forces, amplitude increases. The strong correlation between the change in wavelength and the underlying topography makes it possible to estimate the bathymetry from the measured wavelength. Normally available global bathymetric maps (e.g., ETOPO-1 bathymetry toposheets) are out of date and provide bathymetry at a very coarse resolution. In this letter, swell wave refraction phenomena using Radar Imaging Satellite C-band SAR data over coastal regions of Mumbai have been studied. The wave-tracing technique has been used to derive the wavelength of swell waves in near-shore regions and analyze the wavelength change in order to retrieve underwater topography using dispersion relation with swell wave properties. This SAR-based technique can be used to derive high-resolution bathymetric maps for near-coastal regions. Also, with this technique, temporal variations in the seabed can be measured to infer geological processes.