Abstract
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.
Highlights
Numerous studies on microwave emission from foamcovered ocean surface have been carried out over the past decades [1]–[10]
We valid the numerical computation for special case where the water fraction and bubble size in foam layer are extremely small such that the emission from foam-covered ocean surface is solely from the planar seawater surface
It is seen that the sensitivity to water fraction in foam layer is higher at Ka-band than that at L-band
Summary
Numerous studies on microwave emission from foamcovered ocean surface have been carried out over the past decades [1]–[10]. Wilheit [4] derived a formula for microwave emission from foam-covered ocean surface considering the surface reflectivity that depends on the wind speed and frequency. These empirical models generally ignore the microscopic structure of foam, and when compared to laboratory experiment [5], they tended to underestimate the emissivity. These models have been applied in satellite data assimilation [6] today for their easy use
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