A scanning hyperspectrometer is an instrument that simultaneously records radiation in hundreds of narrow spectral channels. When studying the water surface, it is commonly used to determine impurity concentrations and detect oil films. At the same time, optical methods for measuring sea wave characteristics usually require contact calibration or operate only in the sun-glitter zone. This study demonstrates that a scanning hyperspectrometer can be additionally used for wave diagnostics under diffuse sky illumination, with its spectral channel enabling simultaneous detection of surface pollutants that affect wave dynamics. Processing was performed on field data from the Oka River and the Black Sea. Surface slopes are retrieved from relative fluctuations of spectral radiance, which provides absolute slope values without contact measurements and compensates for spectral absorption features. Spectral analysis allowed separation of wind waves and slicks, as well as estimation of current velocity. Analysis of slope histograms at different distances from the observer revealed the wave-slope shadowing effect. Two slope retrieval models are proposed, including a new refined model that accounts for sky brightness gradients. This refined model yields a wave spectrum consistent with contact wave-gauge data. The technique is promising for integrated monitoring of water areas, including the detection of surfactant films.
To assess the accuracy of the modeling hydrophysical fields, a comparison of three types of conservative approximation schemes for advective terms in the motion equations was made. These schemes ensure conservation of energy (Experiment 1), potential enstrophy (Experiment 2), and both energy and potential enstrophy (Experiment 3). A numerical simulation method of the Black Sea circulation was applied by using the Marine Hydrophysical Institute model. Three diagnostic simulations with realistic boundary conditions for 2016 were performed, and the results were compared with each other and with observational data. It was found that based on all three schemes, the experimental results were close to each other and qualitatively corresponded to the observational data. Validation of the reconstructed hydrophysical fields using measurements of the temperature, salinity, and current velocity revealed small quantitative differences from the observational data. An analysis of the circulation energetics showed that the greatest difference occurs in the work of advection and buoyancy forces in areas of intense dynamics (in the periphery of mesoscale eddies and jet currents). From the analysis of the forces balance it follows that the simultaneous observance of the conservation laws of energy and potential enstrophy in the difference problem ensures higher accuracy in describing the Archimedes force work and, consequently, in reproducing the processes of baroclinic instability.
The beaching of large patches of natural and anthropogenic debris following storm events is a phenomenon observed along numerous marine shorelines. Today, such wash-outs are becoming increasingly contaminated with plastic litter, which poses a significant threat to coastal ecosystems. A 22-month continuous video sequence, recorded by an autonomous stationary camera, allowed the observation the wash-outs on the northern shore of the Sambian Peninsula (the Baltic Sea). Hydrophysical and meteorological variables from reanalysis data are analyzed to predict the timing of marine litter beaching using machine learning models. The performance of multiple machine learning models was evaluated to assess their ability to predict the time at which marine litter would be beached on the shore. The accuracy of artificial neural network, random forest classifier and gradient boosting classifier of machine learning models are compared. The random forest classifier model (83.4 ± 7.6 % for F1-score) and the artificial neural network model (81.7 ± 3.9 % for F1-score) appear to be the most efficient models for predicting the wash-out formation and beaching. Sea level, wave direction and steepness are the most significant parameters in training models.
The procedure and results of constructing an acoustic map for water area containing single, multiple, and composite underwater objects using an underwater hydroacoustic vision system are considered in the article. The study was conducted in a scale model of a reservoir implemented in the test tank. The objects were located in the Fresnel zone of an extended linear acoustic array model implemented as a hydroacoustic receiver linearly movable according to a predetermined program. The acoustic reflectivity of the underwater objects was ensured by a single acoustic illumination source. The method for localizing underwater objects is based on wavefront curvature in the Fresnel zone. The acoustic reflectivity of the suspected object location was determined by integrating the spatio-temporal signal field along generating line determined taking into account the delays of the signal wavefront reflected from the object. The feasibility of constructing an acoustic map of the water area and subsequent objects recognition (single, composite, multiple) as well as separating objects from group within the view field of the underwater hydroacoustic vision system are demonstrated. An increase in the contrast of objects acoustic images due to the accumulation of wave energy across the entire signal field has been experimentally confirmed.
Unsteady convection in a two-component medium with significantly different transfer coefficients (e. g., in salt water) is theoretically studied. As a specific example, flows arising in a neutrally stratified medium over a flat inclined surface, from which constant (after switching on) heat and admixture fluxes enter the medium, are considered. A well-known exact solution to the unsteady convection problem near a vertical wall with boundary conditions of the second kind is used, which is generalized to the case of a sloping lower boundary. The complete system of hydrothermodynamic and admixture transport equations is reduced to a linear system due to the symmetry of the problem, without any assumptions about the smallness of the perturbation amplitudes. The linearity of the system allows for the use of the superposition principle — independently considering and summing the dynamic effects of the two components of the medium, which determine the deviations in its density. The solution is expressed in terms of repeated probability integrals. The results, in particular, the direction of the resulting flows, depend significantly on the ratio of the exchange coefficients for different substances. For example, nontrivial situations are possible where positive buoyancy influxes nevertheless lead to the emergence of downward currents. Flow turbulence, leading to abrupt changes in effective exchange coefficients, can, in particular, change the direction of convective flows.
The aim of the present study is to develop a method for calculating the diffuse component of the bidirectional reflectance of a strongly absorbing and highly-forward scattering medium like seawater. The relevance of this issue is due to the widespread use of the bidirectional reflectance in the processing of ocean color measurements. Explicit expressions for the first two terms of the expansion are derived. The first term reproduces the well-known result of quasi-single-scattering approximation, and the second corresponds to the contribution of quasi-double scattering (the small-angle multiple scattering before, between, and after two events of large-angle scattering). To validate our analytical results, we carry out numerical integration of the radiative transfer equation for the Henyey-Greenstein phase function, as well as for the two-term Henyey-Greenstein function that models light scattering in seawater. It is shown that for optical parameters typical to seawater, the first two terms of the expansion (i. e. the sum of quasi-single- and quasi-double-scattering contributions) prove to be sufficient to describe the bidirectional reflectance with high accuracy over a wide range of illumination/viewing angles.
The Bussol Strait is the deepest and second-widest strait in the Kuril Islands chain. It dominates in tidal water transport from the Sea of Okhotsk to the North Pacific Ocean, ventilating its waters in layers at depths of several hundred meters. The strait’s mountainous topography and irregular configuration make it appropriate to model it using curvilinear boundary-fitted coordinates, which map the physical domain of the boundary-value problem onto the canonical computational domain. In this formulation, high-resolution modeling of the strait’s extremely active tidal dynamics was performed in a hydrostatic approximation. At the open boundaries of the domain, sea level fluctuations are specified, caused by a total tide containing 14 harmonics over a synodic month of 29.5 days. The initial and boundary conditions for stratification are based on data from a digital climate atlas. Computed tidal currents are analyzed in different phases of the tidal cycle. The maximum current velocities and average water transport through the strait were estimated for the simulation period. The modeling results indicate the important role of the submarine volcanic massif in the strait’s tidal dynamics. The obtained results are realistic to the extent permitted by the hydrostatic formulation of the boundary value problem. In this regard, this work should be considered a preliminary step toward a more representative and complete (non-hydrostatic) modeling of the Bussol Strait’s dynamics.
Several series of numerical experiments were conducted to generate a mesoscale eddy in a deep rotating basin (4000 m deep) with stratification typical of mid- and low-latitude of the World Ocean, including an upper mixed layer, a density jump layer, and a main pycnocline. A sea level anomaly driven by Ekman transport convergence was created at the basin’s center by specifying a wind stress configuration typical for a stationary atmospheric anticyclone. Due to geostrophic adjustment, the resulting pressure anomaly generated an anticyclonic baroclinic eddy in the basin, the rotation velocity of which decreased with depth. Numerical experiments varying the horizontal scale of the eddy, the Coriolis frequency, and the stratification parameters yielded a universal relationship between the ratio of the rotation velocity in the surface and bottom layers and the ratio of the horizontal scale of the eddy to the first baroclinic Rossby radius of deformation. Comparing this universal relationship with published estimates of the horizontal scale of mesoscale eddies in the World Ocean from altimetry and shipboard measurements revealed that at low- and mid-latitudes, the rotation velocity typically weakens with depth by more than 80 %. In the presence of a bottom topography disturbance in the form of an abyssal channel under a mesoscale baroclinic eddy, a current arises in the channel whose velocity is significantly higher than the bottom velocity in the undisturbed eddy. The velocity disturbance caused by the abyssal channel is not limited to the channel itself, but reaches the surface, provided that the width of the channel exceeds the first baroclinic Rossby radius of deformation.
The article presents the values of methane concentration in the near-surface layer of atmospheric air directly measured from the board of “Akademik Mstislav Keldysh” research vessel in the Kara and Barents Seas in the summer of 2024. It is the first time when the marine expeditionary data for the Russian part of the Arctic have been compared with the data obtained by “Videomodule” towed unmanned underwater vehicle engineered at the Shirshov Institute of Oceanology of the Russian Academy of Sciences. The analysis shows that bacterial mats in areas of methane seepage in the Arctic have a limited contribution to the increase in CH 4 concentration in the near-surface layer of the atmosphere. Their influence is likely to be noticeable only in shallow areas (up to 50 m deep), where methane can reach the water surface without being fully oxidized in the ocean. At the same time, short-lived peaks (lasting up to several minutes) of elevated CH₄ concentrations are observed, reaching 3 ppm or higher. The main factor influencing the variability of atmospheric CH 4 concentrations is the direction of air mass transport: when air masses are advected from the north and west, minimum CH 4 concentrations (1.98 ppm) are recorded; conversely, when air masses are carried away from the mainland, methane concentrations increase (up to 2.10 ppm when from the Yamal Peninsula).
The paper presents a combined methodology for the operational forecasting of maximum wave height, integrating the strengths of spectral wave models, phase-resolving simulations, and machine learning to address the core limitations inherent in each approach. The procedure begins with a frequency-directional wave spectrum obtained from the WAVEWATCH III model, which is subsequently transformed into a wavenumber field and used as initial conditions for the phase-resolving model TRIDWAVE. This step enables the generation of a realistic nonlinear wave field from which the target extreme parameter (maximum wave height) is extracted. To circumvent the prohibitive computational cost associated with repeatedly executing the phase-resolving model, a feedforward neural network was developed and trained to act as a fast surrogate, learning the mapping from input wave spectra to the corresponding maximum height values as calculated by TRIDWAVE. Validation experiments conducted for the Baltic Sea demonstrate that the trained network predicts maximum wave height with an average relative error of approximately 5 %. This result confirms the network’s capability to accurately infer key nonlinear statistics directly from linear spectral input.
This paper reviews the principal results of recent studies conducted in Russian marine waters utilizing marine profiling lidars developed at the P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences (IO RAS) and its Saint Petersburg branch. Field experiments with IO RAS shipborne and airborne lidars were carried out in the coastal zones of the Barents, Kara, Okhotsk, and Black Seas, as well as in Avacha Bay in the Pacific Ocean, and focused on addressing contemporary problems of lidar remote sensing. The use of marine lidars for the assessment of hydrooptical characteristics of the near-surface layer, the detection and parameterization of internal waves, and the investigation of the effect of survey-track length on bathymetric lidar mapping in remote high-relief coastal areas are examined. A distinctive feature of the IO RAS systems (shipborne PLD‑1 and airborne APL‑3) — is their two-channel receiving subsystem, which enables separate recording of the polarized components of lidar signals. The implementation of the developed digital signal-processing modules has permitted automation of the lidar-surveying workflow. The scientific relevance and practical importance of these issues underline the need to advance domestic remote-sensing technologies, in particular for lidar surveys conducted from autonomous, unmanned underwater, surface, and aerial vehicles.
A solution to the problem of the thermal regime of the forming oceanic lithosphere during sedimentation on its surface is presented. This allows us to assess the causes of the significant contrast in sea depths in the Nansen and Amundsen Basins, located in the Arctic Ocean on either side of the Gakkel Ridge. This paper examines the role of both the gravitational load and the thermal insulation effect of the accumulating sedimentary cover on the formation of the relief of the basins surrounding the ridge. It is shown that neglect for the thermal effect of sedimentation on sea depth in the basins in isostatic models leads to errors of several hundred meters. Estimated sea depths in the Nansen and Amundsen Basins, calculated for lithosphere of different ages, taking into account both the gravitational and thermal effects of sedimentation, are comparable to actual depths. The calculated differences in sea depth at reference points in the central regions of both basins are also close to the actual depths.
This article is devoted to developing the foundations of a nonlocal hydrodynamic approach to describing hydrophysical processes and fields in the ocean, based on rigorous results of nonequilibrium statistical mechanics and adaptive systems control theory. Experimental studies and theoretical work in the second half of the twentieth century established that the ocean, influenced by solar energy, celestial bodies, and the Earth’s rotation, and interacting with the atmosphere, complex bottom topography, and coastal boundaries, is an open nonequilibrium system. The multi-scale processes occurring in the ocean under the influence of these factors are highly nonequilibrium and together lead to the self-organization of the ocean. Classical continuum mechanics methods and their modifications are currently used to describe ocean dynamics. This allows us to solve a number of practically important problems. However, the differential models developed are valid for describing systems whose state is close to the local thermodynamic equilibrium. Therefore, they are not suitable for describing the formation of turbulent eddy-wave structures, and attempts to apply classical hydrodynamic models to describe highly nonequilibrium processes lead to solutions that are inadequate to nature. The development of a nonlocal hydrodynamic approach allowed us to formulate a closed-loop formulation of the problem of self-organization of a dynamic structure in an open system. This formulation consists of integro-differential transport equations with model integral kernels. The model parameters, which determine the sizes and lifetimes of the medium’s dynamic structure, satisfy nonlinear differential evolution equations according to the speed gradient algorithm. Internal control is formed in the system through feedback between the structural dynamics and the hydrodynamic behavior of the medium. The formulation is supplemented by the initial parameters of the medium’s structure and the initial rate of its deformation. Based on the developed nonlocal hydrodynamic approach to the description of highly nonequilibrium systems, principles for the application of nonlocal models to describe a complex of processes and phenomena in the ocean are formulated.
This publication is a step in the creation of a representative catalog of historical Neva floods, which will be necessary for future flood forecasts as part of the study of the functioning of the complex dynamic system comprising the atmosphere, hydrosphere, and lithosphere of the Baltic-Ladoga region. The article describes the initial phase of the development of a 19th-century flood database, modeled on the 18th-century database created at the St. Petersburg branch of the Institute of Oceanology and now in use by researchers. The complexity of the study stems from an objective shortage of water level data relating to the first quarter of the 19th century.
This study addresses the need for experimental validation of the formation mechanisms of bistatic target strength in axisymmetric objects. A laboratory experiment investigating the secondary hydroacoustic field of an axisymmetric elongated body in a bistatic configuration was conducted in the hydroacoustic tank of the St. Petersburg Branch of the Shirshov Institute of Oceanology, Russian Academy of Sciences. The aim of the experiment was to estimate the bistatic target strength of the axisymmetric elongated body at various body rotation angles and different bistatic angles of the receiving measurement hydrophone. A dedicated experimental methodology was developed, and the necessary equipment for signal acquisition and processing was prepared. The amplitude characteristics and duration of the model echo signal were measured at frequencies of 50–70 kHz for bistatic angles ranging from 10° to 70° and body rotation angles from 0° to 180°. The dependence of bistatic target strength on the bistatic angle and the rotation angle of the axisymmetric elongated body was analyzed. Relationships between the bistatic angle, the body rotation angle, and the characteristics of the echo signal were established. The obtained results make it possible to refine near-field models of bistatic target strength formation and to assess the influence of geometric and spatial factors on the characteristics of the scattered acoustic field. The experimental relationships can be used to optimize the configuration of transmitting and receiving elements in multistatic underwater surveillance systems. The results provide a comprehensive assessment of the spatiotemporal characteristics of echo signals from axisymmetric objects and may be used to improve underwater surveillance technologies.
The paper addresses a critical challenge in wind wave modeling — the need for accurate representation of energy input from wind and wave energy dissipation. It is emphasized that reliable incorporation of these processes is essential for improving the accuracy of operational wave forecasting models and for assessing risks associated with extreme wave events. The study introduces specific parameterizations for energy input and dissipation, implemented within the three-dimensional potential wave model TriDWave, which is based on nonlinear Euler equations in a periodic domain. Energy input is computed using a modified Miles theory, while dissipation is modeled via an operator triggered in near-breaking wave regions, facilitating rapid surface smoothing. Long-term numerical simulations demonstrate that incorporating these parameterizations enables realistic modeling of wave field evolution under steady wind forcing, including the reproduction of total energy growth, spectral peak downshift, and the formation of waves with characteristic vertical and horizontal asymmetry. The presented approach establishes a foundation for developing more refined physical parameterizations in wave models and contributes to the creation of reliable wind wave forecasting systems.
The paper proposes an approach for automatic estimation of the parameters of short-period internal waves using a combination of correlation processing and numerical methods. The application of the method of cross-correlation processing to determine the propagation delay of short-period internal waves is considered, and the application of numerical methods to estimate the direction of propagation of short-period internal waves is described. The sensitivity of the cross-correlation processing method to noise was evaluated using simulation modeling, which showed that this method provides an estimate of the propagation delay with an accuracy of at least 10 % for a signal-to-noise ratio of at least 1.75. Two variants of the numerical solution of the problem of determining the direction of propagation of short-period internal waves are described. The approach has been tested by processing in situ data obtained from drifting thermal profiling buoys. The results of estimating the parameters of the velocity and direction of propagation of short-period internal waves obtained by the analytical method, the numerical method and the method of compressible intervals have been compared, which showed their good convergence. It is noted that the described approach is promising for implementation in real-time monitoring systems.
The review systematizes research from the last decade on modeling the non-radioactive impact of nuclear power plants (NPPs) on cooling water bodies. It examines modern approaches to numerical modeling, including adapted hydrodynamic models and original domestic developments for assessing thermal and chemical impacts. Based on the analysis, promising directions for the development of modeling tools in this field are formulated, such as: incorporating feedback with atmospheric processes to improve forecast accuracy in coastal zones with complex wind circulation; developing models of interaction with bottom sediments; integrating with ecological risk models to transition from assessing abiotic parameters to direct forecasting of impacts on specific species and populations of aquatic organisms; creating detailed forecasts for extreme hydrometeorological scenarios under changing climate conditions to assess ecosystem resilience; and actively applying models at pre-investment stages of designing new NPPs to optimize the siting and configuration of discharge and water intake structures to minimize potential environmental impact.
Quantitative estimates of the Lake Ladoga ecosystem response to changes in climatic atmospheric forcing and external nutrient loads were obtained for the period 1980–2020. The estimates were obtained using the MITgcm three-dimensional hydrothermodynamic model combined with the SPBEM biogeochemical module adapted to the phosphorus-limited conditions of the lake. Numerical experiments were conducted using the following three scenarios: 1) a reference scenario with realistic changes in the external nutrient load and atmospheric forcing for 1980–2020, 2) with realistic changes in the external nutrient load and the “average” intra-annual course of atmospheric forcing for this period, and 3) with realistic changes in atmospheric forcing and a constant external nutrient load equal to the average value for the period under consideration. The results of the study demonstrate a pronounced dominance of the external nutrient load as the main factor determining the dynamics of the lake ecosystem characteristics in 1980–2020. The contribution of climate change to the highly deterministic linear trends of the change in winter phosphate concentrations, summer phytoplankton biomass, and annual phytoplankton production in the photic layer amounted to only 24 %, 10 %, and 21 %, respectively. According to the calculation results, there is a noticeable decrease in these characteristics of the lake ecosystem in the second half of the considered period 1980-–2020. At the same time, a noticeable (more than 20 %) compensating effect of climate change is noted for phytoplankton production, leveling out part of the effect of the decrease in nutrient load. It is shown that non-diatoms, which make the main contribution (63 %) to the total phytoplankton production, strongly respond to climatic changes in water temperature in the considered period. Diatoms show less dependence on climate change, maintaining a close relationship with winter phosphate reserves.
This study derives analytical formulas for estimating the loads exerted by a bore and a solitary wave on a fixed, partially immersed body. These estimates are required in the design and operation of coastal structures. The formulas are obtained by fitting results from extensive numerical simulations spanning variations in body submergence, body length, and incident-wave amplitude. We consider runup heights on the front and back sides of the body, as well as the horizontal and vertical components of the resultant wave force. The bore and solitary-wave problems are solved using one-dimensional shallow water models based on the first and second long-wave approximations, respectively. We report the average and maximum relative errors of the formulas and compare their predictions with results from previous studies. These comparisons demonstrate that the proposed formulas are applicable across the parameter ranges considered.
