RADAR IMAGING OF SAND WAVES ON THE CONTINENTAL-SHELF EAST OF CAPE-HATTERAS, NC, USA

Imaging radars, under certain environmental conditions, can provide an extensive description of shallow submarine topography. In this invest igation, sand waves were observed in shallow water and under light win ds, weak flow, and highly stratified conditions with an L band synthet ic aperture radar and X band real aperture radar. An analysis of the r adar data reveals that regularly spaced modulations seen in the imager y are a result of bathymetric forcing. These modulations appear as a g roup of bright linear east-west trending features approximately 5 km i n length and spaced 230 m apart with observed peak modulations exceedi ng predicted modulations by 7 dB. Bathymetric measurements extracted f rom shipboard ADCP data confirm the existence of sand waves in this re gion. Results from the ADCP data reveal an east-west orientation of th e sand wave crest with lee slopes facing north. Mean wavelengths are 2 30 m and the heights are roughly 2.5 m. The radar modulations lead the sand wave crest, by approximately 135 m suggesting a possible upstrea m hydrodynamic effect, which is consistent with an observed Froude num ber less than one. This study shows that bathymetric effects are obser ved in radar imagery at low current speed, light winds, and strong str atification, demonstrating the critical nature that topographic and st ratified hydrodynamic effects have on radar image interpretation in th e littoral environment. Published by Elsevier Science Ltd.