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.

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.

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 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.

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.

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.

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.

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.