A experiments were performed in the shelf zone of the Black Sea in 2015 to study variability of the current fields and other characteristics of sea bulk, wind waves, and the near-surface atmospheric layer. Region with the secluded underwater hill streamlined with currents was selected. Measurements were carried out from the onboard of vessels on move and in drift by optical, radar, acoustic equipment, and STD probe.<p> </p> The complex different structure of waters, which was formed under the influence of shelf waters and water of the open sea interaction, was observed during the experiment. The analysis of measurements in the water column showed that that the flow around underwater elevation forms the hydro-physical disturbances of marine environment. Maximum flow observed above the slopes of underwater elevation and reach 50 cm/s. Wind speed varied from 0 to 10 m/s. <p> </p>On radar panoramas in the region of underwater elevation is observed the appearance of the wave structure, different from the background wind waves. This anomaly on the sea surface is connected with non-uniform current in the neighborhood underwater elevation.
A experimental laboratory study of the effect of a horizontally inhomogeneous current on breaking statistics of wind waves was carried out. Were creating a current having the same direction as wind waves with positive and negative gradients and a current of the counter direction with a negative gradient. The wind speed varied from 10.4 to 20.1 m/s based on a standard height of 10 m. The maximum current velocity near the surface was 27 cm/s. The maximum current gradient was equal to 0.09 1/s. The codirected current reduces the wind wave amplitude for all wind speeds, while the frequency of the spectral density maximum of wind waves remains the same. The frequency of the recorded by radar wind-wave breaking also decreases for positive, negative, and zero gradients. In the case of counter directions, for light winds in the presence of a current the wind wave amplitude reduces, the wind wave spectrum displaces in the direction of lower frequencies. At higher wind speeds, there were neither differences in the surface wave spectra in the presence and absence of a current, however, an increase in the frequency of the recorded by radar wind-wave breaking is observed. These laboratory investigations are carried out in the interests of the remote diagnostics methods development of inhomogeneous currents at higher wind speeds.
At present time radar methods of the seas and oceans diagnostics are actively developing. Using of the radar stations based on satellites and planes allows to receive information on a sea surface and a atmosphere near-surface layer with coverage of big water surface areas independently of day time. The developed methods of satellite radio images processing can be applied to marine radar stations. In Institute of Applied Physics RAS works on sea surface diagnostics systems development on the basis of standard marine radar are actively conducted. Despite smaller coverage of the territory in comparison with satellite data, marine radar have possibility to record spatially temporary radar images and to receive information on a surrounding situation quickly. This work deals with results of the researches which were conducted within the international expedition in the Atlantic Ocean in the autumn of 2012 on a route Rotterdam (Netherlands) – Ushuaya (Argentina) – Antarctica — Ushuaya. During this expedition a complex measurements of a sea surface, a atmosphere near-surface layer parameters and subsurface currents in the wide range of hydroweather conditions, including the storm were carried out. The system developed in IAP RAS on the basis of a marine radar ICOM MR-1200RII and the ADC (Analog Digital Converter) block for data recording on the personal computer was used. Display of a non-uniform near-surface current on sea surface radar images in storm conditions is shown. By means of the high-speed anemometer and meteorological station the measurements of the atmosphere parameters were carried out. Comparison of the anemometer data with calculated from radar images is carried out. Dependence of radar cross section from wind speed in the wide range of wind speeds, including storm conditions is investigated. Possibility of marine radar using for surface waves intensity and ice situation estimates also as icebergs detection is shown.
Both the modulation of short wind wave breaking in the long surface wave field and the occurrence of breaking in the
presence of a long wave were investigated in wind-wave tank. Short wind waves were generated by the air flow at
various speeds, the long surface wave at various frequency and amplitude were generated by wave maker. Data of X- and
Ka-band scatterometers, string wave recorder placed in the probing area, and web camera making video records of the
probing area were synchronously recorded in the experiment. Also precision measurements using laser-optics system
based on the high-speed video recording, laser illumination, and special algorithms of video processing allowed us to
obtain a large ensemble of the wave profiles. It is shown that at relatively weak wind long surface wave causes short
wind wave breaking, and at high wind speeds – breaking intensification. Wind wave breaking is mainly observed on the
front slope of the long wave, the breaking observation area extends with increasing wind speed.
Complex experiments were performed in the north-eastern part of the Black Sea and in the south-eastern part of the White Sea to study variability of the current fields and other characteristics of the sea, wind waves, and parameters of the near-surface atmospheric layer. Measurements were carried out from the onboard of the scientific research vessels by optical, radar and acoustic sensors. The heterogeneity of bottom topography in Black Sea had quasi-one-dimensional character. The case of the two-dimensionally heterogeneous relief of the bottom was investigated in the White Sea. The peculiarity of these experiments was simultaneous measurements from onboard of vessel synchronously with acquisitions of synthetic aperture radar (SAR) images of the Envisat and TerraSAR-X satellites. We have detected for the case of the quasi-one-dimensionally heterogeneous current a difference between the sea surface roughness above the shelf zone and the roughness at the deep bottom. We found that the inhomogeneities of the bottom topography can manifest as a change not only in the amplitude of different characteristics of surface wave and atmospheric near-water layer, but also in their frequency spectrum. In White Sea the special features of the flow of the powerful tidal current (up to 1 m/s) around the secluded underwater elevation and the spatial structure of surface anomalies in the field of these two-dimensional-heterogeneous currents are analyzed. The numerical simulation of the wind wave transformation in the field of two-dimensional- heterogeneous flows is carried out. The qualitative agreement of the calculation results with the experimental data is shown.
The full-scale investigations of the action of internal waves and inhomogeneous currents on the wind waves and the
near-water layer of the atmosphere were carried out in the White Sea in 2009 - 2011 yr. Measurements were carried out
from onboard of the scientific research vessel "Ekolog" by optical, radar and acoustic equipment. Hydrometeorological
conditions during observations varied essentially. Wind speed varied from 0 to 15 m/s, speed of current from 0 to 1 m/s.
Data about the field of current during different phases of tide are received. Internal waves and their manifestations on the
sea surface are registered. The special features of the flow of the powerful tidal current (to 1 m/s) around the secluded
underwater elevation and the spatial structure of surface anomalies in the field of these two-dimensional- heterogeneous
currents are analyzed. Data about a change in the characteristics of reflected from the sea surface radar signal in process
of development of wind waves are received. Experiments on procedure finalizing of the determination of sub-surface current speed according to the numerical data of radar measuring complex on the base of ship radar Icom MR-1000 and FURUNO 1942 MK2are carried out.
Experimental evidence of millimeter-wave phase conjugation by resonantly enhanced degenerate four-wave mixing(DFWM) is presented for the first time. Nonlinear millimeter-wave interaction was caused by saturation of transitionbetween rotational levels of gaseous carbonyl sulfide (OSC). For radiation with A = 1.64 mm phase-conjugatereflectivity of about 0.4 % has been observed at the gas temperature 200 K, and under optimal pressure.