Mr. Vladimir A. Dobrokhotov Profile

Vladimir A. Dobrokhotov

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Proceedings Article | 12 September 2021 Poster + Presentation + Paper

Wave tank modeling of the damping of gravity waves due to ice floes in application to ocean remote sensing

Stanislav Ermakov, G. Khazanov, V. Dobrokhotov, D. Vostryakova, T. Lazareva

Proceedings Volume 11857, 118570U (2021) https://doi.org/10.1117/12.2600164

KEYWORDS: Radar, Remote sensing, Fluid dynamics, Wave propagation, Motion analysis, Wave sensors, Pollution

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It is well known that marginal ice zones are characterized by different forms of initial stages of ice such as, e.g., grease and fragmented ice which act as surface wave absorbers and thus affect microwave radar backscattering. As a result, mapping of boundaries between solid ice and open water areas using radar may become rather complicated. Another aspect of the problem of wind wave damping due initial stages of ice is that the areas of strong wave damping due to ice can be erroneously interpreted as surface pollutions in radar imagery. Studies of wave damping due to ice floes are still insufficient, and relations between the floe geometry and wave damping are poorly established. The motivation of this study is to improve our understanding of the process of wave damping due to ice floes for elaboration of physical models of wave damping. New wave tank experiments were carried out to investigate the damping of regular mechanically generated waves and of irregular wind waves due to drifting floe imitators (washing sponges) as well as for the case of stationary, non moving floes. Dependencies of the damping coefficient on wave frequencies for regular and wind waves for different floe sizes and different areas occupied by the floes were obtained. One of the most interesting results was that the damping coefficient indicated a local maximum when the floe size was about half the wave length. A physical interpretation of the results was given, based on the analysis of floe movement under the action of the orbital wave motion taking into account the floe added mass.

Proceedings Article | 20 September 2020 Poster + Paper

Ka-band radar backscattering from breaking waves: wave tank study

Stanislav Ermakov, Vladimir Dobrokhotov, Irina Sergievskaya, Ivan Kapustin, Alexander Kupaev

Proceedings Volume 11529, 115290S (2020) https://doi.org/10.1117/12.2574167

KEYWORDS: Radar, Backscatter, Ka band, Microwave radiation, Scattering, Turbulence, Doppler effect, Remote sensing, Applied physics, Modulation

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The role of wave breaking in microwave backscattering from the sea surface is a problem of great importance for development of theories and methods of the ocean remote sensing. Recently it has been shown that the microwave radar return is determined by both Bragg and non Bragg scattering components, and some evidences have been given that the latter is associated with wave breaking. However, our understanding of different mechanisms of the role of wave breaking on small-scale wind waves (ripples) and thus on the radar return is still insufficient. This paper presents results of laboratory experiments on the influence of wave breaking on Ka-band radar signals. An effect of the radar return suppression after wave breaking has been revealed and attributed with wind ripples suppression by breaking waves. The experiments were carried out in an oval wind wave tank where intense m/dm-scale surface wave trains were generated by a mechanical wave maker, in particular using a method of dispersive wave focusing. Wind waves were independently generated in the wave tank. A Ka-band radar was mounted at a height of about 1 m above the water level the incidence angle of microwave radiation was about 50 degrees. The experiments were performed both for a clean water surface and in the presence of an oleic acid monomolecular film. It has been obtained that the radar return before the wave train was determined by wind ripples, the radar Doppler spectrum was centered close to the Bragg wave frequencies. The radar signal intensity was strongly enhanced in a wide frequency range when the train was passing by the study area. After the intense wave train the radar return dropped and then slowly recovered to the initial level. We believe that the attenuation of radar backscattering after the wave train is due to suppression of wind ripples by turbulence and surfactants associated with wave breaking.

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