Comparison of submarine relief features on a radar satellite image and on a Skylab satellite photograph

Publisher Website
Google Scholar
Abstract
We compare satellite imagery obtained by an optical sensor and by synthetic aperture radar for a shallow ocean area showing submarine relief features. A Skylab photograph and a Seasat radar image of the North American cast coast (Nantucket Shoals) taken at different dates, but at the same tidal phase and under comparable weather conditions, are analysed. It is shown that the radar imaging as well as the optical imaging is caused by roughness variations of the water surface due to tidal flow over submarine relief. It is investigated whether optical imaging is affected by backscattering by suspended sediment in the water column, by reflection from the sea floor or by variations of the surface roughness associated with wind and tidal flow over underwater bottom topography. We conclude from the analysis of the densities in the blue, green and red layers of the Skylab colour film that specularly reflected sunlight at the rough ocean surface is the dominant imaging mechanism. In cases where the underwater bottom topography has an influence on surface water waves, the slope distribution of these waves cannot be explained by the Cox-Munk model alone because it only describes the relation between windspeed and slopes of the water waves. Therefore we suggest here that perturbation of the mean square slope spectrum caused by current gradients can explain the brightness modulation in the optical imagery.