AN IMPROVED COMPOSITE SURFACE MODEL FOR THE RADAR BACKSCATTERING CROSS-SECTION OF THE OCEAN SURFACE .2. MODEL RESPONSE TO SURFACE-ROUGHNESSVARIATIONS AND THE RADAR IMAGING OF UNDERWATER BOTTOM TOPOGRAPHY

In the companion paper we have presented an improve composite surface model for the calculation of normalized radar backscattering cross sec tions (NRCS) of the ocean surface. The proposed model accounts for the impact of the full two-dimensional ocean wave spectrum on the radar b ackscatter and was shown to reproduce measured absolute NRCS: values f or a variety of radar configurations and wind speeds satisfactorily af ter some reasonable tuning of the input ocean wave spectrum. This pape r focuses on the modulation of the NRCS in the presence of spatially v arying surface currents. First, the sensitivity of the NRCS to intensi ty variations of different ocean wave spectral components is investiga ted. Then the hydrodynamic modulation of the wave spectrum over underw ater bottom topography in tidal waters is computed in different ways, and the resulting radar signatures are discussed. The composite surfac e model yields comparable radar signatures at high (10 GHz, X band) an d low (1 GHz, L band) radar frequencies, which is in much better agree ment with experimental results than the predictions of a first-order B ragg scattering model. On the other hand, measured variations of the N RCS at high radar frequencies appear to be still underestimated in som e cases, which may be due to shortcomings of our description of the wa ve-current interaction by conventional weak hydrodynamic interaction t heory. Possible improvements of the theory are discussed, and requirem ents for future experiments are formulated.