Reconstruction of Sea Surface Relief and Sea Wave Spectra Using a Sea Surface Image

We consider a method for diagnosing sea waves based on processing of spatiotemporal images of the sea surface in scattered light of the sky with a grazing angle of observation. An original method of reconstructing wave slopes and sea surface relief which does not require information on parameters of optical receiver and absolute values of sky brightness has been developed. The method is based on formation of relative fluctuations of sea surface brightness in the approximation of linear dependence of the sea surface brightness on wave slopes. A polarization method for increasing the contrast and accuracy of determining wave slopes in an image of sea surface is proposed. This method was tested in full–scale conditions using the example of processing spatiotemporal images of the sea surface in scattered light of the sky, and the relief of sea surface slopes, i.e., the spatiotemporal distribution of wave slopes, was obtained. We propose a method for determining the time spectrum of long waves by integrating the spatial frequency spectrum of the spatiotemporal relief of the sea surface in the vicinity of a parabolic dispersion curve. This method of calculating the time spectrum of wave slopes makes it possible to distinguish long waves that obey the dispersion relation and get rid of unnecessary noise that can be contained in the optical image (stripes, breakdowns, wave group structure, slicks, nonlinear distortions of the transfer function of sea surface brightness to wave slope, etc.). The wave elevation spectrum obtained by the optical method and the synchronously recorded wave elevation spectrum obtained using a string waveform are compared. The variability of statistical characteristics of the visible slopes of long waves with the distance from the optical receiver is studied.