Breaking waves effects on scatterometer and radiometer signatures of the ocean

Active and passive microwave signatures of the ocean depend on the ocean wave spectrum alone if bound and breaking waves are neglected. History has not been kind to attempts to explain both radiometer brightness temperatures (T_b) and the normalized radar cross section (σ_o) of the sea using the same ocean wave spectrum. In this paper, we show that bound and breaking waves can be included in previous models of radiometer and scatterometer microwave signatures of the ocean to allow a single wave spectrum to explain both T_b and σ_o. Bound waves are the roughness produced by gently breaking, or crumpling, waves that travel near the speed of the parent wave while breaking waves are more violent. Breaking wave and foam modeling both build on the function Λ(c_b) introduced by Phillips, which describes the average length of breaking wave fronts on the ocean per unit area as a function of breaker velocity, c_b. We model a form for Λ(c_b), particularly around its peak, based on experimental shapes, the speed of the interference pattern produced by the wave spectrum, and the balance between wind input and dissipation described by the spectrum and Λ(c_b). Thus the wave spectrum completely determines Λ(c_b). We show that the result of including bound and breaking waves in radiometer and scatterometer models of oceanic signatures is a much closer fit to data using a single spectrum.