In the coastal areas of Peter the Great Bay (the Sea of Japan), the influence of ice thickness, snow cover on its surface, and the concentration of chlorophyll a in the layer under ice on the value of subglacial illumination at 60 hydrological stations from January to March 2010–2016 was studied. Deglacial illumination was determined using remote sensing methods, which allowed us to conclude that the seasonal averages of illumination in the studied region are sufficient for the development of phytoplankton under ice. The influence of a hole for measuring parameters under ice on subglacial illumination is estimated. It was shown that the “hole effect” did not appear at depths below 2 m. Measurements were performed from ice at hydrological stations using the autonomous probing system SBE-19plus (Sea-Bird Electrons. Inc., USA). The attenuation of illumination was evaluated in two two-meter layers by the coefficients: K₂₀ — (logarithm of the ratio PAR2/PAR0 — “ice+ice water”) and K₄₂ — Lg (PAR4/ PAR2) — in the water layer between horizons of 2 and 4 m. A direct relationship was established between the weakening of the illumination and the thickness of the ice in the case of an experiment in one day (03.11.2010). The coefficient of determination was positive and significant. If we compare these parameters throughout the winter period, a meaningful relationship could not be established. Presumably, other factors are superimposed on the relationship between illumination and ice thickness. We have confirmed that one of these factors is the concentration of chlorophyll-a in the subglacial layer of water. The daytime interval was also revealed when the subglacial illumination does not feel much dependence on the deglacial illumination.

This paper proposes a method to retrieve water temperature and salinity in the Azov Sea using the results of hydrodynamic modeling, in situ data, and satellite images of the visible spectrum range. The results of simulations performed with the three-dimensional hydrodynamic model Princeton Ocean Model by atmospheric reanalysis SKIRON are presented. Long-term monthly average in situ measurements of temperature and salinity for the period 1913–2012 were used in the simulation as initial conditions. In situ data are used in the hydrodynamic model as initial temperature and salinity fields. The assimilation of these data into the model is based on long-term average values averaged for each month of measurements and grouped into arrays related to the surface, mid-sea and bottom layers of the sea. Preliminary in situ data analysis was performed, including a description of long-term seasonal variability of temperature and salinity in the Sea of Azov. The procedure for assimilation of satellite data from MODIS L2 into the hydrodynamic model based on the established relationship between the sea salinity and bio-optical features is suggested. The research shows the advantages of the proposed joint use of satellite data and the results of assimilation modeling to obtain continuous information on the thermohaline structure of water in the Sea of Azov.

The article presents the results of an analysis of inter-annual changes in the monthly means of bio-optical characteristics in the surface layer of the Barents, Kara, White, Baltic, Black and Caspian Seas for the period 1998–2018, calculated from data satellite color scanners. As the main parameters, the chlorophyll-a concentration, Chl and particle backscattering coefficient, b_bp = b_bp(555), characterizing the variability of phytoplankton and suspended matter, are discussed. The other characteristics, such as the absorption coefficient of colored organic substance a_g = a_g(440) as an indicator of river runoff, the parameters that characterize the phytoplankton bloom (coccolithophore blooms in the Barents and Black Seas, of blue-green algae in the Baltic Sea) are also considered. The monthly means of sea surface temperature, SST by MODIS-Aqua data are presented as a parameter characterizing climate change. Most of the bio-optical characteristics were calculated using regional algorithms, derived from field measurements carried out in the considered seas and reflecting their regional features.
The presented data revealed significant changes in bio-optical characteristics that occurred in the considered seas in 2016–2018, in most cases they were associated with phytoplankton blooms. Systematization and analysis of extreme changes in bio-optical characteristics over the entire observation period found a record change in the southern part of the Caspian Sea in July 2001 after the invasion of the ctenophore Mnemiopsis — the chlorophyll concentration increased by more than an order. Another factor contributing to the record variability of bio-optical characteristics is river runoff.
The obtained results provided quantitative data on changes in bio-optical characteristics in the period 1998–2018 for six seas, different in their natural conditions, and provided the basis for further analysis aimed at identifying the processes and factors that caused these changes.

The paper shows the results of optical measurements carried out during the coccolithophore bloom and the primary bio-optical characteristics obtained. Blooming coccolithophores produce a significant amount of mineral suspension, increasing light scattering and reducing the transparency of water. An increase in the backward scattering leads to an increase in the upwelling radiance and the reflectance coefficient of the sea water. Field measurements were carried out on an oceanographic platform located 600 meters from the coastline in July 2012 and May 2017. The measured parameters included light beam attenuation coefficient, sea reflectance, and the Secchi disk depth, satellite data from MODIS scanners Leves 2 and 3 were also used. The measured beam attenuation coefficient was twice higher than in the absence of the bloom, the reflectance was three times higher. Measured values show similar temporal variability. The calculations of the primary bio-optical characteristics were carried out using semi-analytical algorithms. The coccolith concentration was estimated in various ways; the results and their temporal variability are in good agreement. The calculated backscattering is an order of magnitude higher compared to the absence of the bloom, while the GIOP model somewhat underestimates the calculated values. The combined use of satellite and contact data makes it possible to restore both total scattering and backscattering. The asymmetry coefficient of the scattering and the backscattering ratio show an increase in the fraction of small particles with a high refractive index.

The paper deals with a comparative analysis of the data on in-situ measurements of spectral water transparency in the range of 400–800 nm for some sections of Lake Teletskoye water area during stable summer and winter temperature stratifications. Field trips were conducted in summer of 2016–2019 and during the freezing period of 2018. The description of the device developed for measuring spectral underwater irradiance by depth at wavelengths of 303, 361, 590 and 656 nm as well as the measurement results made in the summer of 2018–2019 are presented. The data on distribution of spectral underwater irradiance by depth at maximum height of the Sun and cloudlessness are given. It is revealed how many times spectral transparency increases during the freeze-up period (when the water area covered by ice) as compared to lake warming in summer. Dynamics of changing relative transparency in sites of the lake’s water area according to white disk is shown for different years. The obtained results make it possible to rank the lake water area by anthropogenic and natural impact of the catchment.

The effect of in water optically active components on spectral downwelling irradiance and on phytoplankton capacity to absorb light has been investigated in coastal waters of the Black Sea near Crimean Peninsula, where spectral light absorption coefficients of phytoplankton, non-algal particles and colored dissolved organic matter were measured in different seasons 2016. It has been revealed, that an increasing of content of optically active components effect on the spectral features of downwelling irradiance — shift of wavelength of the maximum of spectral downwelling irradiance to the longer wavelength on ~25–40 nm, which resulted in ~3 times decreasing of the spectrally weighted chlorophyll-a specific absorption coefficient. It has been shown that change in spectral downwelling irradiance, caused by content of any optically active components, is described by its relationship on ratio between light absorption coefficients of colored detrital matter and phytoplankton pigment (a_CDM(440)/a_ph(440)), which is optical depth-dependent.

Based on in situ measurements of the hydrological and bio-optical characteristics of the marine water, an analysis was made of the variations of the simulated remote sensed reflectance spectra of the sea during the passage of internal waves in the shelf zone of Peter the Great Bay. It has been shown that color indices and remotely determined concentrations of chlorophyll-a have the greatest contrast for remote observation of the manifestations of internal waves in the marine column. The optimal spectral range for satellite identification of the manifestation of internal waves is 440–500 nm. The obtained optical characteristics can be directly used to analyze the period of oscillations of internal waves and their automatic identification in satellite images. The position of the crests of the internal waves can be smeared or shifted, and for its estimation, as well as for estimating the amplitude, it is necessary to solve the inverse problem of remote sensing of the color of the sea, taking into account regional hydro-optical characteristics and the unstable stratification of optically active components in the sea mass, using data from hydro-physical modeling.

Regional bio-optical models of water constituent retrieval for lakes and reservoirs are developed all over the world. It is especially difficult for reservoirs with high spatio-temporal variability of the water optical properties due to heterogeneous currents, plumes and irregular wind forcing. In this case, the usage of the traditional station-based sampling to describe the seasonal state of the reservoir or to validate satellite data may be uninformative or even irrational for a variety of reasons. As an alternative, an original approach based on simultaneous in situ measurements of the remote sensing reflectance by a spectrometer and concentration of water constituents by an ultraviolet fluorescence LiDAR from a high-speed gliding motorboat was proposed. This approach provides fast data collection with high spatial and temporal resolutions, i. e. 8 m and 1 Hz, respectively, from a large area in a short time interval within the spatial distribution of the hydro-optical characteristics do not change. Besides, the presented approach remains efficient in condition of broken cloud coverage. It was successfully applied for develop high-resolution and statistically reliable Chl-a and TSM models by Sentinel-2 and Sentinel-3 images of the Gorky Reservoir as an example of eutrophic productive and highly changeable inland waters.

A method for approximation of the instantaneous shape of a waved sea surface as a superposition of harmonic waves with unknown amplitudes, wave vectors, and phases is proposed. These unknown parameters are determined using glint characteristics, such as their coordinates and areas. It is shown that for a certain ratio of the number of harmonics and glint, these unknowns can be defined as a solution to the derived system of nonlinear equations. Next, the task of restoring an instant image of an underwater object distorted by surface waves is solved. An algorithm has been developed for reconstructing the original image distorted by the waves, based on the approximation of the instantaneous shape of the waved surface. A full-scale experiment was conducted, the results of which showed the efficiency of the method. The reasons that impede a fairly good recovery, and ways to eliminate these difficulties are noted. It is shown that with an a priori known shape of the object, the depth of its location can be determined by the criterion: “as the depth of the best restoration of the shape of the object”. Adding modules to the developed algorithm that take into account the scattering and absorption of light in the atmosphere and in sea water will make it possible to use it for image corrections of underwater objects taken from aircraft.

The greatest variability of the ecological state of coastal waters is observed in the areas of river mouths. River plumes can differ from the surrounding sea water both in the composition of impurities and in their concentration. Moreover, the size and position of plumes are characterized by strong variability. Monitoring of such water areas requires measurements with high spatial and temporal resolution. The possibility of operative estimation of natural sea water components distribution at a river plume by the method of passive optical sensing from board a vessel was demonstrated at the Caucasian coast of the Black Sea. Portable three-channel hyperspectral complex EMMA (Ecological Monitoring of Marine Areas) installed on a gyro-stabilized platform was used for this purpose. The data of the EMMA complex were processed by a special algorithm, which allowed obtaining light absorption spectra of sea water and estimating concentrations of its natural components. The efficiency of the gyro-stabilized complex is discussed in comparison with measurements without stabilization. It has been shown that it is possible to obtain estimates of the concentration of the main natural seawater constituents with a gyro-stabilized complex EMMA under conditions of uneven illumination at low sun position, which significantly expands the time frame for measurements. The presented complex may be useful for ground truth measurements in coastal areas of the ocean or inland seas with river plumes.

In order to conduct environmental monitoring and obtain operational data on the state of the investigated water area, a sounding spectral fluorescence and scattering meter was created. It allows simultaneous measurements of the fluorescence of phytoplankton, dissolved organic matter and light scattering in the sea water, in the spectral range covering the region from the near ultraviolet to the red boundary of the visible spectrum in the same measuring volume.
The results of instrument testing in laboratory conditions on samples of phytoplankton monocultures existing in the Black Sea waters showed good agreement between the measurements and literature data. During the expedition of the R/V “Professor Vodyanitsky”, at 77 hydrological stations the following parameters were measured: vertical profiles of the phytoplankton fluorescence; DOM; the elastic light scattering. As a result, information was obtained on the vertical distribution of the measured parameters in the studied waters of the Black Sea. The results of tests of the presented meter allow to approve the technical design and works methodology of this meter.

A description of the set-up of a new compact optoelectronic device designed for remote registration of sea wave characteristics from the ship’s board is given. The device registers laser radiation reflected from the sea surface in the form of a “fan” using a CCD arrays. The device uses the Oclaro HL63193 laser diode, which operates in continuous mode in the region of 634–637 nm wavelengths with an output power of up to 500 mW. The area illuminated by the laser on the sea surface is a band 3–5 mm wide and 2–3 m long (when placing the device on a ship at an altitude of 6–9 m above sea level). The receiving unit of the device is based on the OP-55AR film projection lens and the Sony ILX554A CCD arrays. The device has been tested in laboratory and marine conditions. It is shown that the speed of scanning the sea surface can be significantly higher (up to 833 Hz) than in previously created models with a narrow beam when using mechanical mirror scanning (7–15 Hz). This makes it possible to increase the speed of data accumulation and thereby reduce the dispersion of the values measured over a given time, which in turn makes it possible to register weaker impacts of hydrodynamic processes on the sea surface. At the same time, the weight of the layout was reduced to 5 kg instead of 35 kg (for a layout with a narrow beam and a mechanical scanner).

The problems of evolution, climate, ecology, global monitoring and remote sensing of Earth are considered as a radiation factor in the interest of World Global Research Projects “Future Earth”. The problems are investigated as related on the basis of radiation transfer theory regarding scattering and absorption of solar and native radiation. The term “Global system”, implemented by N.N. Moiseev, was introduced in theoretical and applied research in the Earth sciences: analysis and synthesis of knowledge about the development of planetary civilization are required. The problem of adequate assessment of the role and authority of simulated subsystems in the long-term evolution of the entire “Global system”, including those related to the Earth radiation field, is of particular importance. The Earth radiation field is a uniform physical field (electromagnetic radiation) and a unifying factor of the Earth dynamic system. Models for accounting of exchange and separation of atmospheric and ocean radiation contributions have been developed. According to experts, the radiation factor of influence on the Earth climate system is from 40 % to 60 %. R.I. Nigmatulin proposed a hypothesis: “Ocean — the dictator of climate”. Н₂О and СО₂, cloud cover and ocean are the main competing factors of radiation forcing. To study the radiation factor of the World Ocean influence on climate change and evolution of the Earth, international cooperation is required with the use of integrated systems for observing radiation processes under water, on water and from space with the support of supercomputer modeling and big data.