Local Analysis of Inhomogeneous Sea Surfaces in Coastal Waters Using Nautical Radar Image Sequences

Abstract

The radar backscatter from the ocean surface (sea clutter) is modulated by the surface wave field. From the spatio-temporal sea clutter pattern, which is recorded by a nautical radar, surface wave spectra, the near-surface current, and in shallow waters the bottom depth can be retrieved. In coastal waters the sea surface is inhomogeneous. Changing water depths induce horizontal gradients of the tidal current. Wave refraction occurs due to the spatial variability of the current and water depth. Currents and the sea state act as forces which induce morphodynamic changes and damage on the shore. Therefore, there is urgent need for a cost-effective, remote-sensing monitoring method. Local image sequence processing algorithms were developed which provide hydrographic parameter maps with a high spatial resolution. The analysis is based on spectral filter and regression techniques which themselves are based on the dispersion relation of water surface waves (inverse modeling). The method is outlined by an example image sequence, which was acquired during a recent storm surge on the seaward side of the island of Sylt.