The Doppler Spectrum of the Microwave Radar Signal Backscattered From the Sea Surface in Terms of the Modified Bragg Scattering Model

Significant progress has been made in the study of electromagnetic wave scattering from the sea surface. Essential results were obtained in solving applied problems, but there are still unsolved problems in the scattering theory. The radar backscatter cross section is usually used to solve remote sensing tasks, although the Doppler spectrum (DS) of the scattered microwave signal contains more information about sea waves. The concept of a two-scale model of the scattering surface is used in this article. Correct allowance for large-scale waves, in comparison with radar wavelength, in deriving theoretical formulas enabled us to develop a modified Bragg scattering model. It is based on the previously developed scattering model that is refined here to take into account the contribution of the horizontal component of the orbital velocity to the DS. It is shown that allowance for large-scale waves limits the growth of the radar cross section of the Bragg component with a decrease in the incidence angle, which allows using the resonant scattering model at small incidence angles. An additional result is that the modified model of the DS can also be used in the range of middle incidence angles because it takes into account the contribution of the horizontal component of the orbital velocity. It is shown that if the correlation between large-scale and small-scale components of sea waves is neglected, the new formulas pass into the known formulas for the DS within the framework of the Bragg scattering model.