Kosnik M. Short wind wave spectra: experimental research and modeling

The thesis is devoted to the experimental and theoretical research of surface wind wave spectra in the range from decimeters to millimeters. A new approach to short wind wave spectrum estimation is developed and realized. The method is based on stereophotography of the sea surface. The spectra obtained from stereophotography are then used for the absolute calibration of the slope spectra calculated from the brightness field of the same areas of images. Such approach allows to extend significantly the range of the observed wavelengths towards the shortest waves that are not principally resolved with the use of classical stereophotography. In result of the experimental data processing using the method proposed, a set of directional spectra of waves of 6 mm - 30 cm range for the winds from 4 m/s to 15 m/s is obtained. The dependence of short wind wave spectrum level on the wind speed is determined. The spectrum level of the short gravity waves is found to be independent from the wind speed while the most sensitivity is observed for the waves with the lengths 1-2 cm. The presence of the "dip" on the curvature spectrum in minimum phase velocity region in natural conditions is confirmed. A numerical study of three-wave interactions of capillary-gravity surface waves is performed. It is found that three-wave interactions are responsible for the "dip" formation on the curvature spectrum in minimum phase velocity region. The obtained reliable empirical information was used for the correction of the physical short wind wave spectrum model.