Coupled Harmonics as a Characteristic of the Nonlinearity of the Wind Wave Field In Remote Sensing Signals

Abstract

We discuss the features of wind wave manifestation in remote sensing signals and the possibilities of estimating the wave field nonlinearity parameters based on the analysis of coupled harmonics. Using numerical modeling of one-dimensional nonlinear waves and backscattered signals at a wavelength of 3 cm at sliding sounding angles, we demonstrate the possibility of reconstructing the orbital velocity field of model waves from remote sensing signals. Spectral analysis of sea wave radar sounding signals under natural conditions demonstrated the distribution of the wave energy by coupled harmonics. The angular dependence of the energy distribution over wind wave harmonics, which is observed in the experiment, is confirmed by previously obtained theoretical calculations. Based on the processing results, it was found that the ratio of the spectral densities of the second harmonic to those of the first is greater than that for the Stokes wave and weakly depends on some statistical parameters of the wave measured by contact means. A conclusion is made about the need to take into account coupled harmonics when reconstructing the wave field structure from remote sensing data.