A Theoretical Model for the Microwave Emissivity of Rough Sea Surfaces

When sea surface wavelengths are not larger than microwave wavelengths, the microwave emissivity of Gaussian rough sea surfaces can be investigated by applying effective media theory (EMT) of rough surfaces. For one-dimensional Gaussian sea surface, the microwave emissivity model is proposed by EMT, which regards the air-sea rough interface as a new effective medium of isotropic permittivity between the top layer of air and the bottom layer of seawater. The emissivity model is controlled by the root mean square deviation (RMSD) of the rough surface height and the correlation length of the rough surface. Results clearly show that the emissivity increases along with the RMSD increase if the latter is smaller than a critical value. Furthermore, excess emissivities and the brightness temperature increments for a wind-roughened sea surface can be estimated from those of flat surfaces by fitting the RMSD as a function of wind speed. Good agreements are obtained by comparing the results of our model with the satellite data at microwave frequencies of 1.4, 6.8, 18, 21, and 37 GHz, respectively. Moreover, these findings imply that our method can be extended to retrieve the sea surface parameters, such as RMSD and the correlation length of the rough surface, from the satellite data.