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A direct optical method for measuring the “instantaneous” profile of the sea surface with an accuracy of 1 mm and a spatial resolution of 3 mm is described. Surface profile measurements can be carried out on spatial scales from units of millimeters to units of meters with an averaging time of 10−4 s. The method is based on the synchronization of the beginning of scanning a laser beam over the sea surface and the beginning of recording the radiation scattered on the surface onto the video camera matrix. The heights of all points of the profile are brought to a single point in time, which makes it possible to obtain “instantaneous” profiles of the sea surface with the frequency of video recording. The measurement technique and data processing algorithm are described. The errors of the method are substantiated. The results of field measurements of the parameters of sea waves are presented: amplitude spectra, distribution of slopes at various spatial averaging scales. The applied version of the wave recorder did not allow recording capillary oscillations, but with some modernization it will be possible. The method is completely remote, does not distort the properties of the surface, is not affected by wind, waves and sea currents, it allows you to measure the proportion of foam on the surface. The possibility of applying the proposed method at any time of the day and in a wide range of weather conditions has been experimentally proved.

Objectives. Capillary waves on the sea surface play an important role in remote sensing, both in the optical and microwave wavelength ranges. However, processes of electromagnetic radiation scattering on a rough sea surface cannot be studied in the absence of reliable monitoring of the parameters of these capillary waves under natural conditions. Therefore, the aim of the present work was to develop methods for such monitoring purposes and test them under laboratory and field conditions.Methods. Novel laser-based methods for recording capillary waves at frequencies up to 100 Hz were developed in the laboratory. The proposed remote methods, which do not interfere with the sea surface, are based on the recording of scattered laser radiation using a video camera.Results. Under laboratory conditions, spatial profiles, time dependences of heights for all points of a laser sweep trajectory, and frequency power spectra were obtained. It is shown that slopes in capillary waves can reach 30° and that the amplitude of capillary waves at frequencies above 25 Hz does not exceed 0.5 mm. A new version of a scanning laser wave recorder was tested under natural conditions on an offshore platform. The measurements confirmed the possibility of measuring the parameters of sea waves on spatial scales covering 3 orders of magnitude: from units of millimeters to units of meters.Conclusions. The developed wave recorder can be used to carry out direct measurements of “instantaneous” sea surface profiles with a time synchronization precision of 10-4 s and a spatial accuracy of better than 0.5 mm. The method makes it possible to obtain large series (21000) of «instantaneous» wave profiles with a refresh rate of 60 Hz, which opens up opportunities for studying the physics of wave evolution and the influence of wave parameters on the scattering of electromagnetic waves. The advantage of the method is the direct nature of the measurement of applicates and other wave characteristics not only in time but also in space. The entirely remote method does not distort the properties of the surface and is not affected by wind, waves, or sea currents. The possibility of using the proposed method under natural conditions at any time of the day and in a wide range of weather conditions has been experimentally ascertained.

The features of the Doppler spectra of radar signals scattered by atmospheric inhomogeneities under clear sky conditions are studied. A technique for measuring the wind field in the millimeter wavelength range using a coherent radar is described. The results of measurements of the radar reflectivity Z under summer convection cannot be interpreted by the theory of Bragg scattering on inhomogeneities due to locally homogeneous isotropic turbulence. The experimental values can exceed the theoretical estimates by two orders of magnitude. An analysis of the fine structure of the Doppler spectra obtained under summer conditions indicates their large width, multi-peakedness, and spatial variability. The authors attribute these features to the formation of thermals, the structure of which is accompanied by closely spaced ascending and descending flows. The high level of radar reflectivity also confirms the convective version of signal generation, in which a large moisture difference in closely spaced ascending and descending layers at the thermal boundary forms eddies with large refractive index gradients.

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