Signatures of Microwave Emission From Foam-Covered Ocean Surface

Good understanding the emission in the presence of foam layer is essential for effective retrieval of oceanic parameter from microwave measurements. In general, microwave emissivity is enhanced by the foam layer, depending not only on the macroscopic dielectric properties and the foam layer thickness, but also on the absorption and scattering of the bubbles. In this paper, a numerical emission model is developed based on a matrix doubling method by which the volume scattering effects in foam layer are accounted for. We explore the effects of the water fraction and foam layer thickness on total emission from foam-covered ocean surface, by analyzing the contributions from both the up-welling and the down-welling emissions from foam layer, and the emission from the seawater. In particular, the dependence of emission, consisting of the three effective emission sources, on the foam layer thickness and water fraction at L-band to Ka-band are investigated. Results are compared with predictions by the incoherent method. Physical reasons given rise to the depolarized emissivity at high frequency bands, and the dry sub-layers at the top of foam layer are discussed.