Analysis of measured and simulated multi-channel radar images of underwater bottom topography from the C-STAR field experiment

A major goal of the joint European project C-STAR is the identification and improvement of weak elements in the suite of hydrodynamic and electrodynamic model components which describes the radar imaging of underwater bottom topography in tidal waters. A field experiment has been carried out over underwater sandwaves off the Dutch coast in order to obtain a comprehensive set of depth profiles, currents, winds, surface wave spectra, and radar images at several channels. In this paper, a first comparison of experimental results with model predictions is presented. While some of the observed radar signatures at P-band (0.45 GHz) can be well reproduced by a composite surface imaging model, other signatures are shown to be clearly underestimated. The available wave data suggest that this behavior is due to an underestimation of the intensity variations of short waves by conventional wave-current interaction theory. Possibilities of improving the theory by accounting for effects like wave breaking, the generation of “parasitic” short waves at the crests of steep longer waves, or a feedback between modulated surface roughness and wind friction are discussed