The present paper is devoted to the development of a multisensory approach to hydrophysical measurements of the ocean surface layer. The combination of coherent acoustic sounding, coherent radar sounding, and optical stereo photography is considered. Each of the methods separately has several advantages, but it is not free from disadvantages. Coherent acoustic sounding, described by resonant scattering, has a large observation area but has a poor spatial resolution. Coherent radar sensing, also described by resonant scattering, has a smaller observation area but a higher spatial resolution. Both methods allow us to recover the velocity characteristics of scattering associated with the velocities of resonant scatterers. Using the relationship between sea surface elevations and orbital wave velocities, it is possible to determine the spatial spectra of wind waves in a wide range of wind wavelengths up to several meters. To determine the characteristics of shorter-scale wind waves, it is proposed to use data from optical stereo photography. As a calibration for the optical system, information on the elevation of the sea surface obtained from coherent acoustic and radar sounding data can be used. Thus, the spatial spectrum of wind waves can be reconstructed in the range of energy-carrying to gravitational-capillary waves. In addition to the spectral characteristics of waves, it is possible to determine the velocity of the near-surface flow by measuring the Doppler shift of acoustic and radar signals. High-resolution data obtained from stereo photography of the sea surface allow clarifying the relationship between the velocities of acoustic and radar scatterers and hydrometeorological parameters.
The present paper considers the possibility of a system for environmental monitoring of film pollution in the Gorky reservoir. A combination of the well-known approachs for calculating the drift trajectories of passive particles on the sea surface with the data of remote sensing, which provides primary detection of a pollution spill in the scanned area is proposed. X-band digital coherent radar was the source of remote data. Based on this radar, an automated radar system is being developed for the automatic detection of film contaminants on the water surface. The results of tests of the algorithm for automatic detection of film pollutions based on field measurements are presented. The model component of the system is based on the results of measurements of current velocities and the physical dependence of the slick drift. As a result of comprehensive studies, the developed system has demonstrated operability for detecting and predicting the spread of film pollution in the Gorky reservoir.
The paper considers the results of a promising method for remote determination of parameters of dynamic processes in the ocean – coherent ocean radar sensing. This work proposes a methodology for determining the speed and direction of the sea surface current and wind waves spectrum by measurements of X-band Doppler radar. Based on the Doppler Effect, it is possible to measure the orbital velocities of wind waves on the sea surface, the velocities of breaking waves, the velocities of the sea surface current and the speed parameters of other oceanic dynamic processes. Using the basic expressions of the wave theory of free waves on water, it is possible to restore the heights of wind waves without additional calibration. Theoretical numerical simulation of the Doppler velocity of the Bragg waves in the field of wind waves and currents were carried out. The simulation used a two-scale model of microwave scattering on an wavy water surface, taking into account the shading of the sea surface by wave crests. A correlation analysis of the surface current, calculated through hydro meteorological parameters and Doppler radar panoramas, showed a maximum correlation coefficient for a velocity value is about 0.88 with a root mean square error of 8 cm/s, and for a direction is about 0.98 with a root mean square error of 14 degrees. The work shows the possibility to recover wind wave spectra from the data on the Doppler shift of microwave radio waves. Features that are not described by the two-scale model are found and discuss.
The article discusses the results of theoretical and experimental studies of Doppler velocity on the sea surface. Doppler
velocity is measured by radar sensing at moderate and low grazing angles. The experiments were performed using
coherent X-band and Ka-band panoramic digital radars operating with the horizontal polarization for transmission and
reception. These radars have high spatial resolution. An algorithm for reconstructing Doppler velocities is proposed and
estimates of the fluctuation sensitivity of the method are carried out. The method is applied to the conditions of the fetch-limited
wind wave growth, which is typical for enclosed waters and the sea nearshore, where the dominant wavelength is
of the order of ten meters. Based on the two-scale model, the dependences of the Doppler velocity on the parameters of
the ocean-atmosphere interface are considered. The effect of shadowing by the crests of wind waves on the magnitude of
the Doppler velocity at low grazing angles is discussed. The manifestation of the orbital velocity of wind waves is
demonstrated.
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.
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.
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.
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