A boundary value problem is solved for the equations of motion, continuity, density constituents and turbulence characteristics in the 3D-domain of the northern Kuril Straits with boundary conditions determined by the solution of the global model. The boundary value problem is implemented by the finite volume method on an unstructured mesh in the hydrostatic approximation. Detailed tidal modelling of the Fourth Strait dynamics is performed in a non-hydrostatic approach. The results represent the velocity fields, residual circulation of the М₂ tidal wave and the summary tide of eight harmonics M₂, S₂, N₂, K₂, K₁, О₁, P₁, Q₁ with a synodic period of 29.5 days. A comparison of the behaviour of the vertical velocity in the tidal cycle of the М₂ wave for two subregions of the Fourth Strait when solving the boundary value problem in the Hs and the Nh approximation was performed. The Hoffmüller diagram of the dynamic characteristics in the synodic month is presented. It has been shown that taking into account the Nh approach, there is a significant change in the transfer of water masses through the Fourth Strait of the Kuril Ridge.

The article analyzes the submesoscale eddies detected in the southern part of Peter the Great Bay in September 2009 as a process influencing the stratification of optically active components in the upper sea layer and the values of the sea brightness coefficients. To analyze the motion of vortices, satellite data of the 2nd level of the average spatial resolution of the MODIS-Terra/Aqua, Merris-ENVISAT-1 spectroradiomers in the fields of sea surface temperature, chlorophyll-a concentration and synthesized RGB images, ship STD data from the SBE19 plus profiler and remote measurements of the spectra of sea brightness coefficients from the handheld hyperspectral radiometer ASD FieldSpec, obtained in a series of coastal expeditions of the POI FEB RAS in September 2009.
As a result, it was found that the eddies are characterized by lower salinity and increased content of colored dissolved organic matter, which may be associated with the influence of the Tumannaya River runoff. The greatest contrast of the vortex relative to adjacent waters is achieved at a wavelength of 412 nm according to remote sensing data. In addition, the contrast is noticeable in remote measurements of chlorophyll-a concentration. The depth of the vortex was 5—7 meters and is completely within the observation area from the satellite in the visible spectral range.

A very high-resolution modelling of the northern Baltic Proper shows that in summer the cyclonic and anticyclonic submesoscale coherent vortices (SCVs) with the extremum of vertical vorticity in the surface layer are formed, while the subsurface anticyclonic SCVs in the shape of convex lenses in the density field prevail over the cyclonic SCVs – concave lenses, with the vertical vorticity extremum in the cold intermediate layer below the seasonal thermocline and above the permanent halocline. In winter the seasonal thermocline and cold intermediate layer are replaced by a relatively deep convectively-mixed layer which makes the formation of subsurface concave cyclonic and convex anticyclonic lenses impossible there. Instead, the winter-time cyclonic SCVs with the vertical vorticity extremum at the surface dominate. The core of winter-time cyclonic SCVs is characterized by a negative temperature anomaly throughout the mixed layer. During its life cycle lasting up to several months and more, the modelled SCVs can repeatedly merge with other SCVs of the same sign of vorticity, and the merger makes the eddy stronger thereby contributing to its longevity.

The article discusses the basic principles of creating modern systems of operational oceanography. The set of basic principles is presented in the form of methodological foundations for constructing operation oceanography systems as applied to the tasks of underwater observation. The properties of such systems, which are fundamentally important for applications in the field of marine observation systems, are characterized. Some problematic issues are discussed. Links of operational oceanography tools to a number of applications are considered. Among the tasks, attention is paid to acoustic underwater observation, optical instruments and models, biochemical processes and models. Among the basic principles, one of the most important is the consistent integration of local models and systems into regional systems and further into global systems, as well as the interface between models and systems at different levels. Attachment and interface processes are accompanied by refinement of initial and boundary conditions using assimilation of in-situ data. The quality of the output results of applied systems depends on the quality of assessments of the state of the oceanic environment and is the basis for the presentation of requirements for the accuracy (uncertainty) of operational oceanography systems. The analysis of the sequential transfer of uncertainty from estimates of the ocean environment to the uncertainty in the output of applied underwater observation systems is also a basic principle. The consistency and practical usefulness of operational oceanography systems in underwater observation tasks are directly related to meeting the requirements coming from applications. The quality of operational oceanography systems is associated with the procedures of adaptive sampling of natural data and adaptive modelling.

The article concretizes the existing methodological approaches to the practical application of oceanological data in areas characterized by high environmental variability during the search by sonars. Quantitative characteristics of the operational oceanology output parameters are formed, based on the analysis of publications devoted to their description. These parameters are taken as initial data for solving optimization tasks. The general statement of the optimal control of sonars in the conditions of spatial and temporal environment variability problem is formulated. The solution of the optimal control problem using the zoning method and the mathematical apparatus of the search theory is given. The role and place of hydroacoustic calculation systems in solving the optimization problem is shown. The volume of the observation zone is proposed for use as a universal parameter characterizing the influence of the environment on the sonar efficiency. An example is given illustrating methodological approaches to optimizing the sonars in solving the search problem by a mobile observer in an ocean area with high spatial and temporal variability. Conclusions are drawn about the possibility of extending the methodological approaches given in the article to optimize sonars located on several mobile observers, as well as to solve the problem of optimizing the secrecy of the observer’s actions in the conditions of spatial and temporal variability of the environment. In conclusion, recommendations for the construction of software and hardware-software tools that provide the solution of applied problems using operational oceanology data are given.

A statistical method for evaluating the efficiency of matched field processing is proposed, based on the evaluation of the probabilistic characteristics of random indicator SINR, the probabilities of which are distributed in accordance with the law of the minimum value of Gumbel. The statistical method is intended for processing data from field tests or model studies of sonar receiving systems. The evaluation of the probabilistic characteristics of indicator SINR is based on statistical analysis of the results of matched field processing in purpose to estimate the parameters of the distribution of this indicator in specific operating conditions of the sonar. Examples of the use of the method in modeling matched field processing are given in order to solve problems of comparing the processing quality under conditions of mismatch between the properties of model and real waveguides, as well as the presence of random errors when measuring the parameters of the waveguide. The simulation of the processing results was carried out using the SonarMFP software package, designed by SPIIRAS-HTR&DO Ltd to calculate the ambiguity function of the acoustic signal source as a result of matched field processing with using geographic information system technologies. It is shown that the obtained results allow us to quantitatively compare the receiving systems, operating under different conditions, using probabilistic measures. The method can also be useful when developing requirements for information support of receiving systems based on the principles of matched field processing.

Laboratory analysis and random sample processing of field records of surface ships noise collected in the waters of the White, Barents, and Norwegian Seas were used in the study of ultra-slow signal fluctuations’ influence on the passive listening noise stability. Experiments show that signal fluctuations enable a potentially high noise stability when a short accumulation time interval (a few seconds) and a long accumulation time interval (one hundred and more seconds) are used simultaneously. A long accumulation time reduces the likelihood of contact loss during a decrease in the signal level. A short accumulation time can provide significant gain in the detection range during periods when the fluctuation process leads to a short-term increase in the signal level.

The article presents the results of experimental and theoretical researches on the propagation and reception in underwater sound channels (USC) of broadband impulse signals based on pseudo-random sequences. Analysis of the experimentally obtained impulse responses indicates the presence of prerequisites for increasing the noise immunity of receiving navigation and command signals, as well as increasing the range at a constant power. The purpose of the specially performed experimental work was to obtain initial data to improve the efficiency of long-range navigation systems by optimizing the characteristics of the emitted signals. The features of the formation of impulse responses when receiving signals with different frequency bands and durations of symbols, as well as the dynamics of the structure of responses at displacements of the depth of the receiving hydrophone relative to the USC axis, have been investigated. On the basis of ray representations, a physical interpretation of the obtained experimental results is carried out for practical application in solving urgent problems of underwater acoustics and oceanology.

A classification of known solutions of the Pekeris boundary value problem obtained in various model formulations is given, and their comparative assessment is given. To verify various model solutions, an experimental study of the energy and spatial structure of the sound field in a shallow sea in the infrasonic frequency range of 2—20 Hz, which is obviously lower than the first critical frequency of the Pekeris model waveguide, was carried out. The results of experimental studies of sound fields using combined receivers, forming a vertically oriented 3-element antenna, are analyzed. Based on the results of the analysis of the vertical structure of the sound field, it was concluded, that the sound field at the extremely low frequencies of the infrasonic range is formed by inhomogeneous Rayleigh–Scholte waves, regular and generalized. As the frequency increases, the depth of penetration of the sound wave into the bottom half-space decreases and the role of inhomogeneous waves of the Pekeris waveguide, excited by the complex angular spectrum of the source, increases. Such waves appear as hybrid waves, but only with a generalized description of the sound field in a non-self-conjugated model setting. The kinematic characteristics of the sound field are analyzed with a refined definition of the group velocity as the rate of energy transfer. The mechanisms of a significant slowing down of the energy transfer rate in the waveguide at low frequencies are discussed.

The present paper continues a series of studies on using underwater images of the sky (Snell’s window) to retrieve characteristics of wind-driven waves and their variations in the field of near-surface hydrophysical processes and under influence of surfactant films. Research is based on the previously developed mathematical models of the Snell’s window image and two statistical moments, the Elfouhaily spectrum of wind-driven waves, the Ermakov model of wave damping by a thin film, and the Cox-Munk result for a thick oil film. Varying wind, wave, and film parameters in the numerical experiment, we demonstrated a sensitivity of considered statistical moments to changes in wind-wave conditions and viscoelastic characteristics of films. To distinguish film influence from wind weakening having similar manifestations, a series of real underwater images demonstrating the changes in the spot structure with the passing surfactant film through the observed sea surface area were analyzed. The obtained results demonstrate that presented method can be useful in practice for detecting surfactant films with the help of optical recorders fixed under the buoys, for example.

A method for processing a shipborne radiometric polarization lidar signals has been developed. The method allows to perform reliable and fairly accurate determination the position of the boundary between layers with different hydrooptical characteristics. The method is based on the analysis of the time dependence of the echo signal decay. This makes it possible to register changes of the boundary position in the absence of a high scattering layer. Model calculations of lidar echo signals for two-layer stratification of hydrooptical characteristics has showed sharp changes in the time dependence of the echo signal decay in the region of the boundary between the layers, which is especially pronounced for the cross-polarized component of the echo signal. A long-term cycle of lidar sounding of the seawater was performed. The accompanying measurements of the hydrophysical characteristics and the light attenuation coefficient by the Seabird SBE25 with a transmissometer in the experimental area showed the presence of a boundary between the layers at depths of 15—17 m, confined to the pycnocline depth. Processing and analysis of the resulting array of lidar sounding data made it possible to record periodic changes in the position of the boundary between the layers. The maximum recorded amplitude is 3 m, and the average oscillation time period is 8.5 min. The obtained values are typical for internal waves observed in the shelf zone of the Black Sea.