Estimation of Underwater Topography Using Satellite High Resolution Synthetic Aperture Radar Data

A method is presented to obtain underwater topography for coastal areas using state-of-the-art remote sensing data and techniques worldwide. Synthetic Aperture Radar (SAR) data from the new German satellite TerraSAR-X with high resolution up to 1m are used to render ocean waves. As in shallow areas, bathymetry is reflected by long swell wave refraction governed by underwater seabed structures, the depths can be derived using the dispersion relation from observed swell properties. To complete the bathymetric maps, optical data of the QuickBird satellite are used to map extreme shallow waters, e.g., in near coast areas. The implications of remote sensing data for bathymetry estimation from SAR and optical data are based on different physical backgrounds and mathematical applications, but the results complement each other. The optical data provide depths in shallow water from 0m to about 20m depending on underwater reflection during calm weather condition. The depths estimation from SAR covers the areas between about 100m and 10m water depths depending on sea state and acquisition quality. The depths from about 20m to 10m are the domain where synergy of data from both sources can be applied. In our study we present the processing of a depth map for Rottnest-Island, Australia. Radar data from TerraSAR-X and optical data from QuickBird satellite have been used. The depths estimated are aligned on two different grids: a uniform rectangular mesh of 150m horizontal resolution, which corresponds to average swell wavelength in a SAR image and on the irregular mesh of 150m resolution for deeper SAR domain up to ~20m depth and 2.4m resolution for the shallow domain imaged by optical sensor. These new imaging techniques provide a platform for the mapping of shallow marine bathymetry over a broad area at a scale that is relevant to marine planners, managers, and offshore industry. The information about detected shallows like reefs and bars can be successfully applied for ship security for the near realtime services.