The effect of wave blocking on the mapping of sea bottom topography with imaging radar

Abstract

In 1989 and 1991 the imaging of submarine sand waves off the coast of the Netherlands was investigated with the AIRSAR, an airborne P-, L- and C-band Synthetic Aperture Radar (SAR) operated by NASA/JPL. The sand waves in the test area have an asymmetric slope with their steep slopes oriented towards the northeast. In both experiments the surface current velocity was coming from the northeast. According to existing theory, the steep slopes of the sand waves should be visible as dark bands in the radar images. Only the P-band image of 1989 shows this behavior. The P-band image of 1991 and the L-band images of 1989 and 1991 show saw-tooth shaped modulations. During both experiments the wind was coming from the southwest, so wind and current had opposite directions. Therefore wave blocking or wave reflection is expected to play a role. In this paper it is shown how proper inclusion of the kinematics of the waves can explain, at least qualitatively, the observed modulations. >