Modulation of microwave radiance by internal waves: critical point modeling of ocean observations

Microwave polarimetric radiance measurements of the ocean surface have revealed some characteristic modulations in response to strong internal waves. This paper demonstrates that the major features of these modulations are all consistent with a model that evaluates the response of radiance to the modulation of surface roughness. This is a two-scale model that divides the spectrum of unresolved waves into a short and a long wavelength domain. The short wave "critical point" model, which evaluates resonant interactions occurring when the surface roughness scale and microwave wavelengths are comparable, is based on the solution of Gershenzon et al. (1986), to the simpler problem of determining the effect on the emissivity of a monochromatic wave propagating in direction φ with respect to the incidence plane. The model of the response of radiance to the modulation of long unresolved waves uses the Kirchhoff approximation and Gaussian slope probability function. This second contribution to the radiance modulation is not significant with respect to the dominant features of the observations, but it could contribute to some of the more subtle features.