Microwave emissivity of sea foam layers with vertically inhomogeneous dielectric properties

We present a radiative transfer model for the emissivity of vertically structured layers of sea foam at microwave frequencies from 1 GHz to 37 GHz. The main features of the model are: (1) Continuous variation in the amount of air in the foam layer depth which affects foam emission through vertically inhomogeneous foam properties. (2) Various radiative terms contributing to foam emissivity, such as upwelling and downwelling emissions within the foam layer, emission of seawater beneath the foam, and multiple reflections of these components at the foam layer interfaces. (3) Distribution of foam layer thicknesses. The dependencies of foam emissivity on foam layer thickness and incidence angle are presented. Analysis of the model sensitivity to input parameters shows that its results are most affected by the choice of the void fraction value at the air-foam interface. Comparisons of the model results to published experimental and modeling data show that with fewer model variables and inputs, and with a single tuning parameter, the model performs as well as, or better than, other physical models.