The system of optical devices for remote sensing of near surface layer of the ocean is created. The system consists of a set of original optical devices for recording of range – time – intensity (RTI) images of sea surface from optical sections of the sea surface and camera for the recording of the wave breakings and the sea wave spectra [1-5] by spectral analysis of the sea surface images. These RTI images enable one to receive complete information about kinematics characteristic of various manifestations on the sea surface, including sea surface waves, near surface wind flow manifestations on the sea surface, internal waves (IW) manifestations, oil slicks and so on owing to its ability to screen objects according to their velocity. The recording of wave spectra and temporal variability of the whitecap coverage performs from the photograph of sea surface synchronous with the RTI images of sea surface. A method for retrieval of sea wave’s slopes from RTI images is presented. The system of optical devices is suitable for remote sensing of sea surface from sea platform, ship or vehicle. The brightness angular structure of the cloudless sky is studied based on the model of the sunlight single scattering. These model data are compared to the experimental angular characteristics of the sky brightness obtained due to digital imaging of the horizon from the oceanographic platform. A method for determining the optical thickness of the atmosphere in three spectral ranges of light in real time from the angular height of the horizontal maximum brightness of a cloudless sky recorded with a digital camera was developed. The obtained values of optical thickness can be used in the models of angular distribution of the cloudless sky brightness to provide possibility of retrieval the waves’ statistical characteristics by the remote optical method.
In paper presents a comparative study of the short-scale wind waves spectra, received by means of optical and radiometric methods. The optical method for recording the wind waves spectrum is based on spectral analysis of the optical images of the sea surface with non-nadir observations. An incoherent optical spectrum analyzer developed at the Institute of Applied Physics of the Russian Academy of Sciences is described that allows one to record two-dimensional spectra of the sea surface in real time in the wave number range from 0.3 to 5.0 rad/cm. Wind-wave spectrum retrieval using microwave radiometers was carried out by the method of Non-linear Radiothermal Resonance Spectroscopy (NRRS), which was developed and are improving at present at the Space Research Institute of the Russian Academy of Sciences. Using a set of radiometers-polarimeters of the 3, 5 and 8-mm ranges, provides restoration of the spectrum in the range of wave numbers from 0.39 to 15.0 rad/cm. Synchronous microwave and optical measurements of wind wave spectra were carried out on a marine hydrophysical platform in the Black Sea. The results of the sea wave's spectrum restoration obtained by means microwave and optical technique gave almost identical estimates of the spectral curves level, which also coincide with the model spectra. This fact confirms the consistency of described wind wave's spectra recording methods and the possibility of their use for monitoring the sea surface state in natural conditions.
The system of optical devices for remote sensing of near surface layer of the ocean is created. The system consists of a set of original linear array of CCD-photodiodes for the recording of range – time – intensity images (RTI images) of sea surface from optical sections of sea surface and incoherent two-dimensional optical spectrum analyzer (TOSA) for the recording of the sea wave spectra by spectral analysis of the sea surface images in real time. Two these RTI images with various directions of observations enable one to receive complete information about kinematics characteristic of various manifestations on the sea surface, including sea surface waves regardless of its dispersion relation, near surface wind flow manifestations on the sea surface, internal waves (IW) manifestations, oil slicks owing to its ability to screen objects according to their velocity. The recording of short wave spectra perform by the optical spectrum analyzer synchronous with the RTI images of sea surface. The examples of investigations of long surface wave field, sea wave spectra and manifestations of wind gusts and IW are presented.
The principles of sea surface monitoring by optical images are discussed. The methods for retrieval of sea roughness characteristics and near surface winds by its manifestations on sea surface under grazing angles are given. The optical multi-channel set consisted from synchronized optical receivers with sensibility in various parts of optical spectra was developed. The developed principles of optical monitoring were tested in natural experiments with the optical set.
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.
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.
The method of retrieval of wind speed from sea surface image under diffuse sky illumination is developed. The method consists of two stages: firstly the rms slope is determined by fitting modeled radiance with sought rms slope to measured sea surface radiance and secondly wind speed is determined using the Cox and Munk relation between mean square slope and wind speed. An analytical model of sea surface radiance for visible light is developed taking into account shadowing of surface waves for grazing view geometry. The method was applied to investigation of the structure of near surface wind fields in сatabatic wind flows for ranges from hundreds meters to ten kilometers.
It is known that development of new remote sensing technique for investigation of sea surface
features is an important oceanographic problem. This paper is focused on a new method of analysis of
optical range – time – intensity images (RTI images) of sea surface [1-3].
The RTI image constructed from optical profiles of sea surface is an optical analog of a side-looking
radar image of sea surface but having higher spatial resolution and some possibility for remote sensing of
sea roughness. It is possible to form RTI images with range from some tens meters to tens kilometers
depending on spatial resolution needed. A set of original optical devices for recoding RTI images using
linear arrays of CCD-photodiodes was created [4-6].
The long surface wave fields, breaking of waves, near surface wind field features, eddies, wind fronts,
catabatic winds, ship wakes, oil slicks, manifestations of internal waves on sea surface were recorded and
investigated by this apparatus in inland waters and in the ocean [5-7].
Description of optical system, some new examples of RTI images of sea surface and its analysis are
presented in this work.
The principles of remote sensing of near surface winds by its manifestations on the water surface
under grazing angles were developed. The model of RTI imagery of the water surface based on the
expansion of image intensity on wave slopes and taking into account wave shadowing has been
developed. The analytical dependence of intensity of water surface on wave slope dispersion permitting to
restore velocity of near surface wind was received.
The range – time optical images [1, 2] of capillary waves using artificial diffuse illumination of water surface like
sky illumination was derived in water tank. The software for processing of wave’s images was developed. The
technique for recording splashes appearing for strong winds is developed using range – time surface images.
The developed method can be used for investigation of free and bounded capillary waves, wave’s breaking,
action of internal waves on surface waves [3,4] and scattering of radio and acoustic waves by rough surface in
laboratory and natural conditions. The study of gravity-capillary waves in the tank of the IAP RAS was carried
out employing the developed optical system with artificial diffuse illumination.
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 paper is devoted to the development of remote optical methods for monitoring of sea surface. The technique for
creating of large scale optical range - time - intensity optical images (RTI images) of sea surface under grazing angles of
observation was developed and the optical system for monitoring of coastal zone and inland water up to some tens
kilometers was created;
Various manifestations of near surface wind on the sea surface were detected and its dynamic was observed;
The method for investigation of large scale structure of near water wind from RTI images of sea surface was proposed.
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.
The paper is devoted to the development of optical methods for investigations of surface waves. The no coherent
optical multichannel spectrum analyzer for space - time (3D) spectral measurements of sea surface waves in real
time is developed. The model of space - time (3D) spectra of sea surface short scale wave's optical image taking
into account elevation of the long energy surface waves and comparative measurements of optical image spectra
and Doppler spectra of X-band scatterometer are presented. A method for retrieval of absolute value of long wave
elevations from optical image spectra is proposed.
The high-speed optical system based on linear array of CCD photodiodes for registration space - time images of
capillary waves is created. The data on free and bounded capillary waves derived with this system in laboratory
tank with artificial diffuse illumination is presented.
This paper is concerned with the complex of optical devices for recording of sea waves characteristics in wide range of
wavelength from centimeters to hundreds meter.
The energy spectra of short waves are obtained in real time by spectral analysis of sea surface image with spectral
analyzer operating under no coherent light. The spectral-kinematics characteristics of long energy waves are determined
from optical RTI images (range-time-intensity images) constructed from optical profiles of sea surface.
A model of imaging of the sea surface in diffuse sky light is developed using twoscale approach of sea roughness that
permits to receive new expression for spectra of sea surface wave image. The principles of retrieval of spectralkinematics
characteristics of surface waves from RTI images are developed and method for formation of RTI images
permitted to remove influence of ships tossing is proposed.
The preliminary model of sea wave elevation spectra for wavelength from centimeters to meter derived from spectra of
sea surface images and its changing in wind front is presented. The appearance of group structure of long surface waves
is registered on optical RTI images of sea surface.
The complex of optical devices may be used from shore or ship for monitoring of sea surface roughness in real time.
An image of a sea bottom observed through a rough sea surface is randomly distorted by the refraction of light at the water-air
interface. The negative effect of waves on bottom visibility can be decreased by 'accumulating" image frames.
Realistically the possibility of image accumulation is very limited. As a rule an observer has to deal with random images
distorted by the rapidly changing sea surface. Thus a question arises: Is it possible to retrieve the "real" image of an object
from its distorted image, if an image of the exact water surface distorting the bottom image is made simultaneously?
The present paper addresses the correction of a distorted image of a bottom object, when the water surface relief or the
spatial distribution of surface slopes is precisely known. Additionally a correction algorithm is given for rapidly processing
two-dimensional images, the potential for determining the "instantaneous" spatial distribution of rough sea surface slopes
from its instantaneous image is investigated, and finally an analysis is made relating errors in determining sea slopes from a
single image to the associated quality of image correction for an object observed through a changing sea surface.