Extending ocean RCS models to very rough/breaking surfaces

Conventional two-scale models successfully explain many characteristics of moderate incidence angle microwave backscatter from the ocean surface. However, they inadequately describe sea-spike events. This is significant since sea-spikes have been observed to contribute between 10 to 25% of the mean ocean radar cross-section for Ku-band (14 GHz) measurements made at 45° incidence. Sea-spikes are generally believed to be caused by breaking or near-breaking surface waves. A number of mechanisms have been proposed to explain their occurrence at moderate incidence angles. These include quasi-specular reflections from steep slopes, edge diffraction from sharply peaked wave crests, and increased non-coherent backscatter from shortscale roughness generated by the breaking process. The latter mechanism is the focus of this study. The very rough/breaking surfaces observed during laboratory studies of stationary breaking waves, which may resemble spilling breakers observed in the deep-water ocean, serve as the motivation for this work. Radar backscatter measurements were made along the waves with an X-band (10 GHz) radar at 45° incidence at both HH and VV polarization. The breaking crests had a polarization ratio of about unity and a radar cross-section per unit area (NRCS) of about -6 to -3 dB. This work further investigates non-coherent backscatter from breaking surfaces. The dependence of the NRCS upon short-scale wave roughness is evaluated by applying an exact numerical scattering solver to random rough surfaces ranging from slightly rough ones that are representative of wind waves to very rough ones that are representative of disturbances generated by the stationary breaking waves