LGA scattering from measured breaking water waves: extension to jetting surfaces

Abstract

A numerical electromagnetic technique is used to find the low grazing angle (LGA) microwave backscattering from a series of surface profiles giving the measured time evolution of the crest of a breaking water wave generated in a wave tank. Surfactant was added to the water prior to the generation of the wave, giving more energetic breaking than in previous waves similarly considered. In particular, two well-defined, fairly large jets form during the breaking. The horizontally polarized backscatter exceeds the vertically polarized backscatter as the jets form, giving brief, but large magnitude super events (or "sea spikes"). These events occur although front face of the modeled wave is truncated, eliminating the large-scale multipath to which super events are usually attributed. The Doppler shifts of the backscattering at the two polarizations are also quite different, with the strongest VV signal appearing at the shift associated with the maximum velocity of the jetting, while the strongest HH signals are at lower Doppler shifts associated with the formation of the jets. The shifts from the distributed-surface roughness of the turbulent "Scar" remaining after breaker are that expected from the orbital motion of the wave.