In June 2015, aboard the r/v Akademik Ioffe, a study was conducted on the surface zooplankton community in selected Baltic Sea basins along the Arkona Basin - Gulf of Gdansk route. Samples were collected using a 100 mu m mesh plankton net at depths of 2-0 m. Additionally, optical and physical properties were assessed through remote (lidar) and in-situ (CTD and surface microlayer seawater sampling) measurements to provide a foundation for biological analysis. The zooplankton included 19 taxa from holoplanktonic Copepoda, Diplostraca, Rotifera, and meroplanktonic stages of Bivalvia, Gastropoda, Polychaeta, Cirripedia, and Pisces. Zooplankton abundance ranged from 37399 ind. m-3 (Slupsk Furrow) to 267744 ind. m(-3 )(Bornholm Basin), with copepods being the most numerous groups. While the zooplankton community composition was relatively stable across the study area, their distribution varied. The most diverse station was Slupsk Furrow, with Copepoda, Diplostraca, Rotifera, and meroplankton making up approximately 40%, 25%, 20%, and 5%, respectively. In contrast, Bornholm Basin had the highest zooplankton numbers, mainly dominated by copepods (90%) with minor contributions from other groups. Fluorescence properties of surface microlayer organic matter were assessed by measuring the intensity ratio of the primary fluorophores (A, C, M, and T) of dissolved organic matter molecules, represented as (M + T)/(A + C). This indicated a mixed marine-terrestrial nature of organic matter in stations west of the Slupsk Furrow. Stations at the Arkona Basin and the Slupsk Furrow had the highest ratio values, suggesting a significant marine organic matter source. In contrast, stations east of the Slupsk Furrow exhibited lower (M + T)/(A + C) ratios, indicating a dominant terrestrial origin for organic matter. Lidar results further supported the division of the study area into two regions based on bio-optical properties: a western region (Arkona Basin, Bornholm Basin, and Slupsk Furrow) and an eastern region (Gotland Basin and Gdansk Basin). Moreover, the variability in zooplankton community structure and distribution is closely correlated with the water hydrographic and optical characteristics. We can therefore conclude that all the water properties that we have studied are a derivative of the interaction of sea and land.

В работе представлены результаты исследования изменчивости биооптических характеристик вод средней Волги на участке протяженностью 500 км от г. Нижний Новгород до пгт. Камское устье 9-17 сентября 2023 года. Измерения проводились непрерывно с борта движущегося катера с помощью флуоресцентного морского лидара УФЛ-9. По лидарным данным построены карты хлорофилла “а”, показателя поглощения а(440), как индикатора, окрашенного растворенного органического вещества, и минеральной взвеси для прямого и обратного маршрутов. Указаны диапазоны вариаций, рассмотрено проявление притоков и влияние метеоусловий. The paper presents the results of a study of the variability of the bio-optical characteristics of the waters of the Middle Volga in a 500 km section from Nizhny Novgorod to the village. Kama estuary September 9-17, 2023. Measurements were carried out continuously from the side of a moving boat using the fluorescent marine lidar UFL-9. Based on lidar data, maps of chlorophyll “a”, the absorption index a(440), as an indicator, colored dissolved organic matter, and mineral suspension for direct and reverse routes were constructed. The ranges of variations are indicated, the manifestation of inflows and the influence of weather conditions are considered.

The development of regional satellite bio-optical models for natural waters with high temporal and spatial variability, such as inland seas, reservoirs, and coastal ocean waters, requires the implementation of an intermediate measuring link in the chain, “water sampling—bio-optical models”, and this link must have certain intermediate characteristics. The most crucial of them are the high-precision measurements of the main water quality parameters, such as the concentration of chlorophyll a (Chl a), colored dissolved organic matter (CDOM), and total suspended sediments (TSS) in the upper water layer, together with a high operational rate and the ability to cover a large water area in a short time, which corresponds to a satellite overpass. A possible solution is to utilize laser-induced fluorescence (LIF) of water constituents measured by a marine LiDAR in situ with a high sampling rate from a high-speed vessel. This allows obtaining a large ground-truth dataset of the main water quality parameters simultaneously with the satellite overpass within the time interval determined by NASA protocols. This method was successfully applied to the oligotrophic Issyk-Kul Lake in Kyrgyzstan, where we obtained more than 4000 and 1000 matchups for the Chl a and TSS, respectively. New preliminary regional bio-optical models were developed on the basis of a one-day survey and tested for archive Sentinel-2A data for 2022. This approach can be applied for regular monitoring and further correction in accordance with seasonal variability. The obtained results, together with previously published similar studies for eutrophic coastal and productive inland waters, emphasize the applicability of the presented method for the development or adjustment of regional bio-optical models for water bodies of a wide trophic range.

We present the results of optical studies of organic matter in the surface water layer of Gelendzhik Bay and adjacent areas of the Black Sea. The efficiency of remote laser sensing for determining the relevant grid of sampling stations is shown. A weak contribution of terrigenous dissolved organic matter (DOM) has been established. A slight increase in the concentration of humic substances was demonstrated near the mouth of the Su-Aran River. The maximal content of biolabile DOM is typical for coastal regions in Gelendzhik Bay. In the eastern part of the bay high levels of DOM, particulate organic matter (POM), as well as the maximum content of DOM and POM together, were observed on the basis of fluorescent lidar data.

Atmospheric correction of remote sensing imagery over optically complex waters is still a challenging task. Even algorithms showing a good accuracy for moderate and extremely turbid waters need to be tested when being used for eutrophic inland basins. Such a test was carried out in this study on the example of a Sentinel-3/OLCI image of the productive waters of the Gorky Reservoir during the period of intense blue-green algal bloom using data on the concentration of chlorophyll a and remote sensing reflectance measured from the motorboat at many points of the reservoir. The accuracy of four common atmospheric correction (AC) algorithms was examined. All of them showed unsatisfactory accuracy due to incorrect determination of atmospheric aerosol parameters and aerosol radiance. The calculated aerosol optical depth (AOD) spectra varied widely (AOD(865) = 0.005 − 0.692) even over a small area (up to 10 × 10 km) and correlated with the measured chlorophyll a. As a result, a part of the high water-leaving signal caused by phytoplankton bloom was taken as an atmosphere signal. A significant overestimation of atmospheric aerosol parameters, as a consequence, led to a strong underestimation of the remote sensing reflectance and low accuracy of the considered AC algorithms. To solve this problem, an algorithm with a fixed AOD was proposed. The fixed AOD spectrum was determined in the area with relatively “clean” water as 5 percentiles of AOD in all water pixels. The proposed algorithm made it possible to obtain the remote sensing reflectance with high accuracy. The slopes of linear regression are close to 1 and the intercepts tend to zero in almost all spectral bands. The determination coefficients are more than 0.9; the bias, mean absolute percentage error, and root-mean-square error are notably lower than for other AC algorithms.

The current paper presents the results of a full-scale study of the fluorescence features of pollutants ( diesel fuel, Urals oil), as well as an alcoholic solution of oleic acid, which imitates oil by visco-elastic characteristics. The experiment was carried out on the Gorky Reservoir under conditions of wind waves. Local areas of artificial slicks were created for multiple intersections at different angles to the wind and waves with continuous lidar sounding of the upper water layer. Signals were recorded by the ninth generation UVL-9 laser ultraviolet fluorescent lidar developed by the Institute of Oceanology of the Russian Academy of Sciences. At signal analysis, spectral intensities and fluorescence features of the studied substances are determined, possibilities of slick detecting as well as film thickness estimation are made, examples of surfactant film detecting behind the oleic slick where visual observation of pollutants does not give a result are showed. The obtained results are useful for the further development of fluorescent methods and devices for operational remote sensing of surface pollution on wave water surface.

This paper is devoted to the study of the possibilities of restoring the concentrations of chlorophyll-a (Chl-a) and total suspended matter (TSM) in fresh waterbodies using the images of Sentinel-2 / MSI of the Gorky reservoir as an example, validated via the high-resolution ground-truth data obtained by fluorescence lidar UFL. This water area in the period of intense chromaticity of cyanobacteria is distinguished by their completely heterogeneous spatial-temporal distribution with scales of patchiness from several tens of meters and high temporal variability. For this reason, direct methods of “spot” measurements in place on water samples in a small part of the reservoir for 3 hours relative to the satellite’s span do not provide us with reliable and statistically proved data. In this regard, the work proposed an original method of high-performance sub-satellite synchronous measurements of the brightness of the water column, concentrations of Chl-a and TSM with a fluorescent lidar onboard a high-speed vessel. This technique is provided with a spatial (8 m) and a temporary (1 s) resolution. Based on this, 4 independent regional models for the recovery of Chl-a concentrations, as well as TSM were developed based on in-situ measurements of the brightness of the water surface, or from Sentinel-2 / MSI images. To ensure the possibility of using satellite images, the analysis of atmospheric correction algorithms was performed and the best one was determined. The proposed models can be used for regular environmental monitoring of the Gorky Reservoir according to the in-situ ship measurements of the brightness of the water surface or from Sentinel-2 / MSI images. When using the proposed methodology for lidar high-performance collection of sub-satellite data, the developed models can be adapted for limnological monitoring of other freshwater bodies with high spatial and temporal variability of the optical properties of water.

The possibilities of chlorophyll a (Chl a) and total suspended matter (TSM) retrieval using Sentinel-2/MSI imagery and in situ measurements in the Gorky Reservoir are investigated. This water body is an inland freshwater ecosystem within the territory of the Russian Federation. During the algal bloom period, the optical properties of water are extremely heterogeneous and vary on scales of tens of meters. Additionally, they vary in time under the influence of currents and wind forcing. In this case, the usage of the traditional station-based sampling to describe the state of the reservoir may be uninformative and not rational. Therefore, we proposed an original approach based on simultaneous in situ measurements of the remote sensing reflectance by a single radiometer and the concentration of water constituents by an ultraviolet fluorescence LiDAR from a high-speed gliding motorboat. This approach provided fast data collection including 4087 synchronized LiDAR and radiometric measurements with high spatial resolutions of 8 m for two hours. A part of the dataset was coincided with Sentinel-2 overpass and used for the development of regional algorithms for the retrieval of Chl a and TSM concentrations. For inland waters of the Russian Federation, such research was performed for the first time. The proposed algorithms can be used for regular environmental monitoring of the Gorky Reservoir using ship measurements or Sentinel-2 images. Additionally, they can be adapted for neighboring reservoirs, for example, for other seven reservoirs on the Volga River. Moreover, the proposed ship measurement approach can be useful in the practice of limnological monitoring of inland freshwater ecosystems with high spatiotemporal variability of the optical properties.

An experimental study of statistical characteristics of fluorescent lidar echo signals and spatial distribution of optically active components in waters of the Gorky reservoir at 40 x 10 km experimental area covering the floodplain, channel and estuaries of inflowing rivers was performed. The measurements were carried out during 4 days from 1 August to 4 August 2017 and from 20 September to 22 September 2018 at the stations and continuously along the motorboat track with the help of fluorescent lidar UFL-9 which allows to restore concentrations of chlorophyll a, colored organic matter and total suspended matter in the upper water layer with thickness of about 0.2 to 1.0 m for eutrophic waters. This paper presents maps of their spatial distribution, demonstrating different scales of inhomogeneities, average values and spatial variability of chlorophyll a, total organic carbon and total suspended matter as well as data on variance and spatial spectrum of fluctuations of the elastic backscattering signal. Regressions between mean values and coefficients of variation of suspension and chlorophyll a, and between coefficients of variation of suspension and energy of the elastic backscattering signal are established.

This article focuses on the interaction between the Ob- and Yenisei-dominated parts of the large Ob-Yenisei buoyant plume formed in the southern part of the Kara Sea during ice-free periods. It was shown that certain wind forcing and river discharge conditions cause the formation of a specific structure of the Ob-Yenisei plume with significantly different properties of the Ob- and Yenisei-dominated water masses. Under these conditions, the Yenisei runoff generates a narrow coastal current propagating northward from the Yenisei Gulf along the Taymyr Peninsula, which is isolated by the Ob-dominated water mass from ambient sea water. As a result, the low-salinity Yenisei-dominated water mass occupies a relatively small area, while more saline Ob-dominated water mass spreads over a wide area between the Gulf of Ob and the Taymyr Peninsula. The formation of the “isolation” configuration of the Ob-Yenisei plume described above is presumed to be caused by the eastward Ekman transport and the resulting downwelling flow of the Ob-dominated waters under the low-saline and warm Yenisei-dominated waters along the Taymyr Peninsula. Based on satellite imagery, wind reanalysis, and river discharge data collected and derived for the period of 2005–2011, it was estimated that the “isolation” configuration is regularly formed during late summer and autumn when the Ob discharge to the Kara Sea exceeds the Yenisei discharge and the local atmospheric circulation is dominated by the northerly wind regime. Assessment of the frequency and duration of the occurrence of the “isolation” configuration showed their synoptic time scale and significant inter-annual variability.

We report results of a field survey conducted in the buoyant, sediment-carrying coastal plume generated by the discharge from the Patos Lagoon, the World's largest choked lagoon. The concentration of total suspended matter (TSM) and organic matter (as represented by total organic carbon, TOC) were mapped using an ultraviolet fluorescent LiDAR, which allowed for extensive data coverage (total of 79,387 simultaneous determinations of TSM and TOC) during 3 consecutive days. These observations were accompanied by hydrographic measurements from the ship and at a mooring station. We first describe synoptic variability of the plume, which responded energetically to wind forcing. We then analyze the TSM, TOC and hydrographic data jointly and develop a simple approach to estimate the rates of suspended matter removal from the upper layer due to gravitational settling and turbulent mixing based on relative changes in TSM and TOC concentrations. Four distinct regions within the plume exhibiting different dynamics of suspended and dissolved constituents were identified on this basis.

This article reports the results of three field campaigns conducted in Lake Issyk-Kul in 2015, 2016, and 2017. During the campaigns, CTD profiling and water sampling were performed at 34 locations all over the lake. A total of 75 CTD profiles were obtained. Some biogeochemical and thermohaline parameters at the lake surface were also mapped at high horizontal resolution along the ship's track. In addition, thermistor chains were deployed at three mooring stations in the eastern littoral region of the lake, yielding 147-day-long records of temperature data. The measurements revealed that – while the thermal state of the active layer, as well as some biogeochemical characteristics, were subject to significant interannual variability mediated by atmospheric forcing – the haline structure of the entire lake was remarkably stable at the interannual scale. Our data do not confirm the reports of progressive warming of the deep Issyk-Kul waters as suggested in some previous publications. However, they do indicate a positive trend of salinity in the lake's interior over the last 3 decades. A noteworthy newly found feature is a weak but persistent salinity maximum below the thermocline at a depth of 70–120 m, from where salinity slightly decreased downwards. The data from the moored thermistor chains support the previously published hypothesis about the significant role of the submerged ancient riverbeds on the eastern shelf in advecting littoral waters into the deep portion of the lake during differential cooling period. We hypothesize that the less saline littoral water penetrating into the deep layers due to this mechanism is responsible for the abovementioned features of salinity profile, and we substantiate this hypothesis by estimates based on simple model assumptions.

This article is based on field measurements on the lake Balaton Hungary during the three days: 10, 11, and 12 September 2008. The expedition was performed with the aim to test recently developed ultraviolet UV fluorescent portable lidar UFL-8 in natural lake waters and to validate it by contact conventional measurements. We had opportunity to compare our results with the Moderate Resolution Imaging Spectroradiometer MODIS/Terra spectroradiometer satellite images received at the satellite monitoring station of the Eötvös Loránd University Budapest, Hungary to make an attempt of lidar calibration of satellite medium-resolution bands data. Water quality parameters were surveyed with the help of UFL lidar in a time interval very close to the satellite overpass. High resolution maps of the chlorophyll-a, chromophoric dissolved organic matter and total suspended sediments spatial distributions were obtained.

The article presents results of underway remote laser sensing of the surface water layer in continuous automatic mode using the UFL-9 fluorescent lidar onboard the R/V Akademik Mstislav Keldysh during cruise 59 in the Kara Sea in 2011. The description of the lidar, the approach to interpreting seawater fluorescence data, and certain methodical aspects of instrument calibration and measurement are presented. Calibration of the lidar is based on laboratory analysis of water samples taken from the sea surface during the cruise. Spatial distribution of chlorophyll a, total organic carbon and suspended matter concentrations in the upper quasi-homogeneous layer are mapped and the characteristic scales of the variability are estimated. Some dependencies between the patchiness of the upper water layer and the atmospheric forcing and freshwater runoff are shown.

This work presents an original method for quantifying advection and turbulent mixing of river-borne suspended sediments. The main idea of the method consists in joint analysis of surface distributions of salinity and sediment concentration in coastal areas influenced by river discharge. Basing on the Lagrangian approach we represent a river plume as a set of individual water particles, which inflow from a river mouth, mix with ambient sea water during their motion within a river plume and finally dissipate. Surface salinity and sediment concentration of a particle provides information about its turbulent mixing with undelaying ambient sea waters and gravitational settling of its sediments respectively during the period from its origin in the river estuary till the moment of measurement. Using these integrated Lagrangian characteristics calculated for the whole study area we reconstruct advection streamlines within the river plume and ratio between turbulent mixing and gravitational settling of river-borne suspended sediments. This method was applied to coastal areas situated in the north-eastern part of the Black Sea and the western part of the Philippine Sea. High resolution thermohaline and sediment concentration data were collected using a pump-through system equipped by a CTD instrument and a turbidity sensor.