Estimation of the Wind Wave Spectra with Centimeters-to-Meter Lengths by the Sea Surface Images

V. V. Bakhanov1, A. A. Demakova1, A. E. Korinenko2, M. S. Ryabkova1, V. I. Titov1, ✉

1 Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russian Federation

2 Marine Hydrophysical Institute, Russian Academy of Sciences, Sevastopol, Russian Federation

✉ e-mail: titov@hydro.appl.sci-nnov.ru

Abstract

The method of investigating the sea wave spectra based on spectral processing of the sea surface images made at the diffused sky light is considered. The mechanisms of the sea surface image formation under the oblique viewing are discussed. It is shown that within the framework of a two-dimensional wave model and when the surface is illuminated by a clear sky, the sea surface image spectrum is proportional to that of the wave slopes’ spectrum. Described is the developed in the Institute of Applied Physics, RAS optical incoherent light spectrum analyzer permitting to record two-dimensional spectra of the sea surface images in the real time mode. The spectrum analyzer has a wide dynamic range (up to 40–50 dB). The time required to record one two-dimensional spectrum is 1 sec. When the spectrum analyzer is set up at an oceanography platform or a ship bow, the devise can record the wave spectra ranging from 1 meter to several centimeters depending on the height above the sea level and the viewing angle. The method for reconstructing the wave spectrum absolute values using the test object spectrum is represented. Preliminary results of the wave spectra measurements carried out by the optical method (under different wind speeds) from the stationary oceanographic platform in Katsiveli and from a moving vessel are given. The drawn conclusion testifies to conformity of the obtained wave spectra to the available empiric information on the spectra within the wind wave range under consideration. The obtained wave energy angular distributions and the spectra features observed in the slicks are discussed. To study the features of wave spectrum dynamics, developed is the method for imaging the current two-dimensional wave spectra with high resolution of spatial frequency and wave direction.

Time dependence of the wave angles’ current spectra is represented as the horizontal bands; each of them corresponds to a certain direction of the wave propagation. At that the vertical direction in each band corresponds to the spatial frequency of the wave varying from short to long waves. The brightness of the images is proportional to the slope spectrum in the conventional color scale.

Keywords

sea surface, optics, surface image, surface brightness, processing of images, remote sensing, spectral analysis, wave spectrum, wind waves

Original russian text

Original Russian Text © The Authors, 2018, published in MORSKOY GIDROFIZICHESKIY ZHURNAL, Vol. 34, Iss. 3, pp. 192–205 (2018)

For citation

Bakhanov, V.V., Demakova, A.A., Korinenko, A.E., Ryabkova, M.S. and Titov, V.I., 2018. Estimation of the Wind Wave Spectra with Centimeters-to-Meter Lengths by the Sea Surface Images. Physical Oceanography, 25(3), pp. 177-190. doi:10.22449/1573-160X-2018-3-177-190

DOI

10.22449/1573-160X-2018-3-177-190

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