Remote sensing of wind waves propagating in the areas covered by ice at initial stages of its formation in the marginal ice zone using radar is an urging problem for mapping ice boundaries and their dynamics. Another aspect of the problem is to investigate possibilities of discrimination between the marginal ice zone and oil spills in radar imagery. This study is focused on modeling the damping of surface waves due to ice floes in laboratory and field experiment. Laboratory experiments were carried out is a container filled with pure water in order to exclude the effect of surfactant films on wave damping. The container was mounted on a vibration table, so that surface gravity-capillary waves (GCW) could be parametrically generated in the container when the amplitude of the vibrations exceeded some threshold level. The wave damping coefficient could be retrieved when measuring the threshold. The floes in experiment were modeled using thin plastic pieces of two different sizes, the relative square of the “floe” coverage of the water surface was controlled in experiment. The dependences of the damping coefficient at different relations between the surface wavelength and the floe dimensions as functions of the floe coverage area were obtained. It is obtained that the damping of gravity-capillary waves in the presence of floes comparable in size with GCW can be one to two orders of magnitude greater that the wave damping due to inextensible film. Preliminary field experiments have been conducted on the Gorky Water Reservoir using a research catamaran vessel of the Institute of Applied Physics. Plywood pieces with sizes several times smaller that the studied surface wavelengths were used as imitators of ice floes and were deployed in between the catamaran hulls. Surface waves propagating between the halls were generated mechanically by a vertically oscillating motor boat. The amplitude of attenuating surface waves due to the “plywood floes” was measured with wire gauges mounted at the bow and the stern of the catamaran. The damping distance due to ice floes obtained in the field experiment was estimated as about 10 wavelengths thus indicating that that wave suppression due to the floes was essentially stronger than the viscous wave damping for clean or contaminated water surface. Wave damping observed both in the laboratory and field experiments can be comparable with the wave damping due to crude oil/oil emulsion films, so the problem of discrimination between, e.g. grease ice and oil spills in radar imagery can be nontrivial.
The presented paper is aimed at the possibilities of detecting surfactants fluorescence on a water surface using a
portable UV diode light source and spectrometer. Under controlled conditions of film thickness, a series of laboratory
fluorescence measurements for some surfactant most commonly found in inland waters like crude oil and diesel were
performed. Obtained fluorescence spectra were registered for thin films with a thickness from 0.6 to 33 μm. Estimates of
the fluorescence intensity in relation to film thickness are obtained.
The possibilities of the definition of physical characteristics of organic films on the water surface, including oil thickness estimation, were studied in laboratory conditions based on the novel opto-acoustical approach. It was shown that the continuous infrared irradiation of film on the water surface leads to the generation of ultrasonic wave with frequencies of the order of several kHz which is the result of local heating of subsurface layer of water. The preliminary results regarding a relation between physical characteristics of surfactant films and the characteristics of acoustic wave are presented. A promising approach of remote sensing definition of surfactant films characteristics in real sea conditions was proposed on the base of these results. The development of this approach will contribute to the development of modern systems of strategic remote sensing of the ocean and inland basin.
The goal of current investigation was a study of seasonal variability of remote sensing reflectance in the lake part of the Gorky reservoir, characterized by intense bloom of blue-green algae. The basis of this study includes the data of ship measurements of remote sensing reflectance, euphotic zone and chlorophyll a and dissolved organic carbon concentrations, performed from May 14, 2018 to August 27, 2018 in 7 points of the reservoir, two of which are located in shallow areas with a slow current (floodplain area), two - in the channel and the remaining three - in estuaries of three inflowing rivers. The spatial and temporal variability of remote sensing reflectance is analyzed, its variations are calculated, vertical profiles of chlorophyll a and dissolved organic carbon are constructed, variations of euphotic depth are determined and correlation between variations of remote sensing reflectance and concentrations of optically active components is established
The present work is shown results of estimating the absorption coefficient of water by underwater sky image (Snell’s window image). This paper presents theoretical model of the Snell’s window image, the algorithm to restore the absorption coefficient of water through the static moments of image, the methodology of performing full-scale measurements and processing obtained data and result of testing offered method on the basis of images obtained in fresh internal eutrophic waters of the Gorky reservoir on the Volga River, characterizing by high concentrations of dissolved organic matter and blue-green algae bloom.
A shape of marine slicks is an important characteristic which can be used when solving a problem of detection and identification of oil spills on the sea surface. Slick shape and its spatial-temporal evolution depend on many environmental processes, such as wind speed, nonuniform marine currents, internal waves, etc. In the context of the problem of oil spill dynamics it is very important, particularly at initial stages of oil spill evolution, to describe correctly processes of oil film spreading. Until recently the most popular was the Fay’s model of film spreading which, however, could not correctly explain some obvious effects, e.g., asymmetry of film slicks in the downwind and crosswind directions. In this paper new results of field studies of spreading of surfactant films are presented. The experiments with spills of surfactants were conducted on the Gorky water reservoir using a methodology of contouring slicks with a GPS receiver mounted on a motor boat, and also aerial photography from UAV. The following results have been obtained. First, the effect of elongation of oil spills in the wind direction, revealed in our previous experiment, is confirmed. Quantitative data on growth rates of along- and cross-wind slick axes are obtained characterizing initial stages of the spreading process. Second, new effects have been revealed which are: a) saturation of the cross- and along-wind axes at some intermediate stages of slick evolution, and b) further decrease of the along wind slick axis and the slick square, and a tendency to a circular shape at late stages of the slick evolution. A physical model, explaining qualitatively the observed effects is developed.
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