Предложена методика использования спутниковых радиолокационных изображений Sentinel-1 для оценки затухания длинных гравитационных волн в присутствии фрагментированного ледяного покрова.Методика основана на оценке флуктуаций удельной эффективной площади рассеяния (УЭПР), связанных с модуляцией мощности радиолокационного сигнала длинными океаническими волнами.На основе концепции модуляционно передаточной функции предполагается, что малые вариации УЭПР на масштабах длинных волн пропорциональны амплитуде последних.Затухание волн определённой длины, распространяющихся в заданном направлении, оценивается по изменению их амплитуды на разных участках радиолокационного изображения, направление распространения волн определяется из анализа двумерного спектра радиолокационного изображения морской взволнованной поверхности.

Sea ice in its initial formation stages in the nearshore zone can exist in various forms such as grease ice, snow sludge, and pancake ice. These initial ice forms (IIFs) lead to the attenuation of waves on the sea surface, consequently affecting the intensity of microwave scattering on the sea surface. This complicates the identification of areas covered by IIFs that are situated between consolidated ice and open water. This work aims to analyze wave propagation in the presence of IIFs to develop physical models of wave attenuation. The paper presents a description and results of special field experiments to investigate the attenuation of wind waves of various lengths in the presence of ice simulators. Results of numerical simulation of the attenuation of gravitational waves and a comparison with experimental results are also given. One of the significant findings in the studied dependence of the attenuation coefficient on the ice floe size-to-wave length ratio, observed in both field and numerical experiments, is the discovery of a local maximum for waves with lengths of the order of the “ice floe” size. A physical interpretation of the mechanism of gravitational wave attenuation in the presence of ice floes is proposed, taking into account their attached mass.

3 Волжский государственный университет водного транспорта Нижний Новгород

ФИЦ Институт прикладной физики им.А.В.Гапонова-Грехова РАН

A new approach to the problem of damping of gravity–capillary waves (GCW) on water covered with a layer of viscous liquid (a film) of finite thickness with two elastic boundaries is developed. It is shown that the rotational component of GCW can be described formally as a “forced” longitudinal or Marangoni wave (MW), and the potential component of GCW plays a role of the “external force.” The resonance-like excitation of the forced MW is demonstrated when the GCW and MW frequencies and wave numbers are approximately close to each other. For a film that is thinner than the viscous boundary layers in film, a single forced MW exists that is located within the boundary layer beneath the water surface. For a thick film, the forced MW is characterized by the existence of two spatially separated MW modes: one is localized in the boundary layer below the upper, air–film interface and another within the boundary layers in the vicinity of the water–film interface. Then, at different elasticities of the interfaces, a double peak dependence of the GCW damping coefficient on wave number can occur due to the resonance with the two forced MW modes. The dependence of the damping coefficient on film thickness is characterized by a strong maximum appearing when the film and boundary layer thickness values are comparable to each other. The developed theory is consistent with existing numerical studies and experiment.

It is known that organic and mineral films appear in microwave radar or optical aircraft/satellite images as the areas of reduced intensity due to suppression of short wind gravity-capillary waves (GCW) - slicks. The suppression of GCW with wavelengths ranged from some millimeters to decimeters can be characterized in terms of film elasticity. Hence, marine slicks in radar/optical images can be quantitatively described if the film elasticity is known. The elastic properties of monomolecular films have been thoroughly studied, while the problem for thick films, particularly for crude oil films remains poorly investigated. The latter are characterized by strong inhomogeneity in thickness. This paper is focused on laboratory analysis of GCW attenuation due to non-uniform films. The damping of GCW was measured in laboratory using a method of parametric excitation of standing GCW in a vertically oscillating cuvette mounted on a vibration table. Laboratory measurements were performed for highly inhomogeneous films of pure dodecyl alcohol. When the surfactant concentration exceeded the values corresponding to the saturated monomolecular layer, the surfactant excess was concentrated in non-spreading drops (lenses) of macroscopic thickness of 1-3 mm. The GCW attenuation coefficient was studied for GCW frequencies of 10 to 20 Hz and for different sizes and number of lenses. It was found that the attenuation coefficient increased with the relative area of the lenses. A physical explanation of this effect was proposed based on the “lens-wall” model, when assuming that the lenses reduced the area of the monomolecular film and, accordingly, increased the wave attenuation. Theoretical analysis of wave damping based on a “lens-wall” hypothesis has demonstrated good consistence with the experiment. The effective elasticity of a two phase film -a monomolecular layer with a lens phase- is introduced, which replaces the two-phase film with an effective monomolecular film.