Comparison of synthetic aperture radar (SAR) cross section and wave energy density variations above submarine sand waves from the C-STAR field experiment

During the field experiment in April 1996 of the “Coastal Sediment Transport Assessment using SAR imagery” (C-STAR) project the Experimental Synthetic Aperture Radar (E-SAR) system of the Deutsches Zentrum fur Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Germany, was operated on board a Dornier DO 228-200 aircraft. One of the main objectives was to investigate the applicability of imaging radars for monitoring sea bottom topography in coastal waters in order to study its dynamical behavior. The C-STAR study area is covered by large submarine sand waves. It is located 28 km northwest of Hoek van Holland, The Netherlands, in the southern bight of the North Sea. The authors´ investigation concentrates on a P-band SAR image obtained quasi simultaneously with in situ measurements carried out on board the research vessel Planet and on board the Air-Sea Interaction Drift Buoy (ASIB) system of the Forschungsanstalt der Bundeswehr fur Wasserschall und Geophysik (FWG), Kiel, Germany. The normalized radar cross section (NRCS) modulation of the E-SAR images indicates signatures caused by submarine sand waves via tidal current velocity variations. These NRCS modulations are compared with wave-energy density spectrum variations at the appropriate short surface gravity Bragg-wave frequency measured along the drift path of the ASIB system. These variations are discussed in relation to the sea bottom topography