The results of studies of the dissolved organic matter fluorescence intensity and salinity correlation in the surface layer of the Kara Sea are shown. The studies were carried out using a flow-through system during the cruises of the “Professor Shtokman” and “Akademik Mstislav Keldysh” research vessels (2013—2015). To study the spatial variability of the correlation of colored dissolved organic matter fluorescence and salinity, the method of “sliding correlations” proposed by the authors is used. A strong anticorrelation was recorded in the area of waters affected by river runoff. A positive correlation was recorded in the region of the prevailing effect of the melted glacial waters. In the areas of comparable influence of these factors, as well as outside the desalination zone, no correlation is observed. The interannual variability of the investigated correlation is recorded. The boundaries of the area affected by river runoff are determined from the satellite ocean color data of the MODIS instrument, processed using a regional algorithm for the Kara Sea. Strong anticorrelation in this region, observed over a wide range of salinity, allows the use of satellite maps of the yellow substance absorption spatial distribution to determine the boundaries position of the surface desalinated layer, to study its structure and dynamics.

Hydrodynamic modeling of the Azov Sea water area based on the Princeton Ocean Model was performed to determine the atmospheric impact of the SKIRON model for the period 2013—2014. Based on a joint analysis of the results of numerical modeling and space monitoring from the Aqua satellite (MODIS) data, the features of the space-time dynamics of the optical active matter in the Sea of Azov are investigated. Suspended substances of various origins are manifestedin the total index of light absorption, or backscattering of light by sea water. New algorithms are used to determine the consistency of data obtained by remote sensing methods of the sea surface from space, model solutions and their combination. The program complex implements an algorithm for assimilation of observational data and allows modeling of the process of propagation of suspended and dissolved matter based on the integration of the transport and diffusion equation. Methods of information sharing are discussed, an estimation of the quality of the model forecast is given depending on the intervals of mastering the satellite information. It is shown that a consistent scheme of assimilation of observational data improves the forecast of propagation of suspended solids by the model even with non-informative satellite images. Numerical experiments on the evaluation of multispectral images have shown the effectiveness of the algorithms proposed in the work.

This special issue is dedicated to the 100th anniversary of the outstanding Soviet scientist in the field of atmospheric and ocean optics, Prof. K. S. Shifrin. The content relates only to one of the directions of the many-sided scientific activity of KS. Shifrin, which covered both the electrical properties of semiconductors, and the scattering of electromagnetic waves by particles, and the inverse problems of scattering theory, and propagation of the radiation in the atmosphere, the kinetics of cloud formation and precipitation, and the development of the method of passive microwave thermal radiolocation. The presentations on the main achievements of K. S. Shifrin were made at the special session held within the framework of the XIV All-Russian Conference "Applied Hydroacoustic and Hydrophysics Technologies" (GA-2018), St. Petersburg, May 23-25, 2018. The articles based on these presentations are planned to publish in one of the nearest issues of "Fundamental and Applied Hydrophysics".

A method for probing macro inhomogeneities of the water-scattering coefficient by means of a lidar is proposed, the probing beam of which is modulated in power by a high-frequency narrow-band signal, and the receiver detects the variable component of the backscattering signal at the modulation frequency. The possibility of diagnostics of layered scattering structures in water by means of such a lidar has been investigated. An analytical model of the lidar backscattering signal is proposed and limitations of its applicability are formulated. It is shown that the resolving power of a lidar with respect to the spatial inhomogeneities of the water-scattering coefficient can be estimated from the frequency response of the backscatter signal. Examples of calculation of resolution are given and the range of spatial scales of inhomogeneities that can be resulted by a lidar with a modulated probing beam is estimated. The calculation is based on data on the frequency characteristics of the backscatter signal obtained earlier using numerical Monte Carlo simulations. As the obtained estimates show, the proposed method opens up the possibility of diagnosing inhomogeneities structures with scales previously inaccessible to measurements.

This article presents a brief overview of the recent authors’ works where analytical solutions for the reflection characteristics of summer ice floes with melt ponds in the Visible and near IR have been developed, checked with field experiments and discussed. Sea ice is considered as a statistically homogeneous random mixture of ice, air, and water with a large (in comparison with the light wavelength) scale of inhomogeneities. Within the framework of stereology the inherent scattering characteristics (the attenuation and absorption coefficients, scattering phase functions) of various types of sea ice have been specified analytically. Spectral reflection by ice layers is described within the asymptotic approach of the radiative transfer theory of light propagation in optically thick and comparatively weakly absorbing layers. During melting period the surfaces of ice floes are covered by so called white ice and melt ponds in different proportions. The main factor determining the pond reflection is reflection of its bottom ice. The spectral-angular characteristics of the reflection by both these components (white ice and melt ponds) of Arctic summer ice floes are presented. It is shown that the obtained results are in good agreement with the measurements made in a number of Arctic expeditions, the developed methods of atmospheric correction, which is necessary for processing of both Arctic satellite and field data, being used.

For calculation of the characteristics of light, reflected from a wavy sea surface two approach is commonly used. The first, so called “Method of statistically distributed facets”, that allows only calculating the average values of reflected light characteristics. The second: “Method of specular points” that gives the same result for average of characteristics, but it enables to calculate the fluctuations of theirs. Moreover, the method specular points deals with a visually sensing parameters of surface such as number, location and curvatures of specular points. These parameters that can be derived from glint images allow determining sea surface wave state by solving of direct and inverse problem. Besides, from this parameters can be determined an instantaneous relief of the sea surface, that opens opportunity for formulation and solution new problems.

The present work is devoted to the investigation of the hydro-optical regime of the Gorky reservoir, based on shipboard and laboratory measurements of the characteristics of optically active components and inherent optical properties in 2016 year. The data collected at 97 stations covering more than half the area of the lake part of the reservoir are analyzed. The dominant influence of blue-green algae on the transparency of the water column was observed under the quasi-constant spatio-temporal distribution of dissolved organic matter at the level of 11—12 mg/l and the negligible presence of a mineral suspension. The limits of the Secchi depth variability from 0.2 to 3.5 m respectively algal abundance from 500 to 100 000 cells/ml are established. For this ranges regressions between some inherent optical properties and blue-green algal abundance were constructed as well as formulas for estimating attenuation coefficient and the single scattering albedo by Secchi depth were obtained.

The results of validation of the parameters of coccolithophorid blooms, calculated from satellite observations and field measurements of the spectral radiance reflectance R_rs in the expeditions of the IO RAS in the Barents Sea in 2016 and 2017, are presented. The main parameters under consideration are the concentration of coccolithophoride cells, N_coc calculated with the regional algorithm of the IO RAS and the concentration of Particulate Inorganic Carbon, PIC, the standard product of NASA. Both parameters are calculated through the particle backscattering coefficient b_bp. The performed validation included, first, the estimation of errors in atmospheric correction by comparing the values of R_rs from satellite data and from data measured by ship spectroradiometers. Secondly, the validation of “remote sensing” values of the b_bp and N_coc, using data from direct determination of concentrations of plated cells and detached coccolites. Third, a comparison of calculated values of N_coc and PIC. The obtained results showed that, under favorable weather conditions, it is possible to obtain acceptable estimates of the N_coc from satellite data. To improve accuracy, it is necessary to take into account the features of phytoplankton variability.

Some results of restoration of a vector of slopes of the wavy water surface on its image received under the conditions of a natural lighting at a clear sky are presented. For the experiment an inflatable pool with a diameter of ~ 2 m was used. For the attenuation of the backscattered signal the water is saturated with nigrosine. Images were recorded on a digital photocamera. The waves were created by hand. Except the image of the wavy water surface the photo of the area of the sky, reflected in calm water participates. Distribution of brightness of the sky reflected in quiet water within a photoshot is considered to be a linear. Under the above conditions, a component of the slope vector, collinear to the brightness gradient of the sky, was found. For its finding it was used the image of the wavy water surface and a photo of the same site of water in the absence of waves. The second component was determined directly from the found one, using the fact that both components of the slope vector are derivatives of one scalar function — the function of the water surface elevations. The algorithm used made it possible to find the slopes of waves running in different directions with acceptable accuracy, except for those that propagated near the normal to the sky brightness gradient.

Changes in the transparency of the surface waters of the Black Sea are analyzed on the basis of long-term Secchi depth definitions. The analysis used literature data and the results of definitions during expeditions on research vessels and a stationary oceanographic platform. It is noted that after a catastrophic recession of the surface waters transparency in the early 1990s, a gradual increase in its values occurred, and the situation was returned to the one earlier observed in the 1960—1980. The decrease in transparency was due to the reorganization of the plankton community structure of the Black Sea waters owing to the arrival of large amounts of anthropogenic origin nutrients with the river runoff, as well as the appearance of the invader — ctenophore Mnemiopsis. The subsequent improvement of the situation was due to the crisis phenomena in the economic activity of the coastal countries, and the emergence of the second invasive ctenophore Beroe ovata, which reduced the impact of the ctenophore Mnemiopsis on the plankton community. It is shown that a complete restoration of the ecosystem of the sea did not occur, and as a consequence of this, relapses of abnormal phytoplankton bloom sometimes take place. However, the duration of the ecosystem restoration after relapse is now 3—4 months, unlike the several years in the early 1990s.

The possibility of measuring the frequency-angular spectra of the mode components of random field of small amplitude pycnoclinic internal waves by lidar method is theoretically investigated. Algorithms are proposed for reconstructing the spectra of internal waves from the measured relative power fluctuation spectra of the lidar return signal if the Vaisala frequency and the inherent optical properties profiles are known. It is shown that under certain conditions the frequency-angular spectrum of fluctuations in the power of the return signal arriving from a given depth is represented as a superposition of the frequency-angular spectra of the mode components of the internal wave’s field with weight factors that depend on the inherent optical properties profiles and the vertical mode structure. Therefore, the spectrum of a single-mode internal wave’s field can be determined from the return signal fluctuations from one properly chosen depth, and the multimode field spectrum from signals from several different depths, the number of which should not be less than the number of modes. Formulas for estimating the errors in the determination of the internal wave’s spectrum due to the error in measuring the spectrum of return signal fluctuations, as well as the errors in specifying the unperturbed profile of the light attenuation coefficient and the function characterizing the vertical structure of the mode are presented. The procedure for reconstructing the spectra of the two-mode field is illustrated by a numerical experiment using real hydrological and hydro-optical data obtained in one of the regions of the Barents Sea.

We compared the global and two regional chlorophyll-a algorithms for SeaWiFS and MODIS-Aqua/Terra instruments in the Black Sea based on in situ measurements of the chlorophyll-a concentration (below С_а) in the upper sea layer during 1997—2015. Comparison results for three SeaWiFS, MODIS-Aqua and MODIS-Terra instruments showed: 1) the standard product NASA overestimates С_а throughout the range of variability of С_а in the Black Sea, the average value of the relative error is about 300 %; 2) the product of the Shirshov’s Institute of Oceanology has the same slope in the logarithm axises {С_а(in situ), С_а(algorithm)}, like the standard NASA product, but due to the shift, in the С_а range from 0.2 to 0.9 mg∙m⁻³ is better, in terms of relative error (~80 %) corresponds to observations; 3) the product of the Marine Hydrophysical institute gives the smallest relative error (~40 %), but it has a high sensitivity to the quality of the remote spectral reflectance (R_RS), that is, to the ratio of R_RS in two bands from 480—560 nm.

Estimation of the ecological state of shelf waters or inland seas needs to obtain detailed data over the area operatively. The new three-channel passive optical complex for ecological monitoring of marine aquatoria (EMMA), developed by us, gives the sea radiance coefficient spectra from board a moving ship. For processing of the data of measurements aiming at the water admixtures concentration assessment an original method for solving of the inverse problem is used, which is based on the intrinsic properties of the pure water absorption spectrum — water absorption step method (WASM). Complex EMMA together with the program WASM was applied for studying of the areas of different sea water types mixing in the Black Sea. Giving data at the spacial resolution of 3 meters from board a moving vessel, it enabled us to get the detailed distribution of the natural water constituents over the two coastal regions of the Black Sea with different trophicity under exploration. The obtained remote sensing data were verified with the results of measurements carried out at the stations.