Comparison of geometric optics and diffraction effects in radar scattering from steep and breaking waves

摘要

To address the issue of radar scattering from steep and breaking ocean waves, we developed an efficient and fast 2-D numerical full-wave approach to model both wave evolution and radar scattering from these waves. It enabled us to reproduce the main features of the temporal and polarization behavior of the radar signal such as sea spikes. In addition, to better understand the contribution of multiple scattering that might emerge from radar scattering on steep and breaking waves, we have modeled scattering using a ray-tracing approach that not only provides the ray picture but also supplies both the ray amplitude and the ray phase. This approach eliminates diffraction effects from consideration, leaving only geometric optics effects that include multiple reflections. As a result, angular dependencies of the scattering cross section based on the ray approach were calculated and compared with corresponding values from the full-wave approach. Generally, better agreement between these two approaches is obtained for forward scattering directions than for backscattering directions. Ray simulation for a backscattering direction does not reproduce the HH/VV ratio with the spikes observed in the fullwave solution. This indicates that diffraction effects are critical for explaining important features of backscattering from breaking waves. The role of multiple reflections from the breaking wave profile in creating spikes with an anomalous HH/VV ratio proved to be negligible.