LGA scattering from a steepening water wave-a numerical study

The time-dependent, low-grazing-angle (10°) X-band backscattering from a spilling-breaker water wave is numerically calculated using a hybrid electromagnetic technique that combines the moment method with the geometrical theory of diffraction. The scattering surfaces were detected from photographs of a wave generated in a wave tank. Continuous surface profiles from the initial steepening to post-breaking were used. During the steepening stage and through the formation of a breaking plume both the HH and VV backscatter continuously rise (with HH about 5 dB below VV at all times) and the Doppler shift of the scatter corresponds to the phase velocity of the wave. After breaking freely propagating small-scale waves appear at the wave crest. The magnitude of the VV backscatter remains approximately equal to that before breaking but the Doppler shift drops significantly. The magnitude of the HH backscatter drops dramatically after breaking but the Doppler shift is similar to that observed at VV. The front face of the wave is not numerically modeled so sea-spike events (HH>VV) resulting from multipath interference are not predicted