High Wind and Breaking Wave Measurements with Sar Depolarized Returns

The wind generates a distribution of small slope waves and sporadic steep breaking events. Such double structure of the sea surface is expected to have a strong impact on the radar scattering from the ocean surface. The signature of the double structure is in the wind speed dependence of radar returns: linear for scattering from gentle waves and cubic for breaking contribution. The composite-surface Bragg resonance (CB) theory describes the former very well. Detection of the breaking contribution remains difficult. Here we show that the depolarized (de-pol, or cross-polarized) radar return exhibits the typical double structure, its wind speed dependence increases from linear in low to moderate wind speeds to cubic in high winds. The increased sensitivity of the de-pol returns in high winds is ideal for hurricane wind retrieval. The strong breaking connection offers an opportunity to measure wave breaking and the associated energy dissipation and area of foam coverage from space, their quantification is important for air-sea interaction study and electromagnetic and electro-optical remote sensing.