Translated by E.S. Kochetkova

A 2-dimensional numerical model of stratified fluid dynamics in the vertical plane was used to investigate the structure and internal dynamics of density stratified intrusive current. The intrusion was formed by the pulsed inflow of two identical volumes of water of intermediate density into the two-layer stratified environment with a given time interval. Inflowing volumes of water were marked by different passive tracers. Initial stratification was defined by the density difference between the layers of equal thickness and the thickness of the intermediate layer. A set of dimensionless parameters is proposed which define the initial and boundary conditions of the problem. Numerical experiments showed that the evolution of the intrusive current is significantly influenced by pulsations of the inflow, particularly in the case when the time interval between the pulses is short. Depending on the intrusion parameters both is possible the acceleration and slowdown of horizontal propagation of the second intrusion volume. Dynamics of inflow of the second inflow volume is different for flows with supercritical and subcritical initial Froude number. Calculations show that the pulse nature of the source modifies the flow to the greatest extent when a short time interval between pulses.

The one-dimensional model of boundary layer above sea waves is suggested. The model is based on results obtained before with two-dimensional coupled model of wind and waves. The boundary layer above waves is different of model above flat surface by appearance of additional momentum flux created directly by curvilinear and moving interface. The one-dimensional equations of wave boundary layer can be derived in curvilinear surface-following coordinate system. In this case the equations contain explicitly the specifics of wave boundary layer. The momentum exchange between wind and waves is calculated in spectral space as a sum of separate fluxes, produced by wave modes. It is traditionally suggested that momentum flux is proportional to spectral density of wave energy with coefficient depending on wave age of each mode. The calculations illustrating the specific features of wave boundary layer: velocity and energy of turbulence profiles, wave and turbulent fluxes of momentum. The ratio of external (at upper level of boundary layer) and internal (at surface) roughness parameters is discussed. It is shown that external drag coefficient depends not only on wind velocity but also on shape of wave spectrum, what explains the large scatter of experimental data. Further development of suggested approach for problems of geophysical fluid mechanics is discussed. Such models are intended for coupling of atmosphere and ocean models with wave forecasting models.

For modeling of long-wave impact on hydraulic engineering constructions the boundary value problem in three-dimensional area for the equations of the motion, continuity, constituents of density and characteristics of turbulence is set. The problem is solved by finite-difference fractional time method; non-hydrostatic component of pressure is defined at the final stage by the solution of a boundary value problem for the Poisson’s equation. Calculations are carried out by means of the program system CARDINAL. The boundary-fitted curvilinear grid is used, in the vertical direction s-transformation is used. Characteristics of turbulence are calculated with the help of k-e model. The numerical method is tested on simplified examples. Assessment of influence of non-hydrostatic pressure component is made with calculation of extreme tsunami on a water intake of nuclear power plant El-Dabaa, Egypt projected on the Mediterranean coast and calculation of the velocity field during the storm surge in the navigation canal of St.-Petersburg Flood Protection Barrier. It is revealed that in non-hydrostatic solution at an entrance to narrowness, on a bottom raising increase in vertical velocities from bottom to surface, causes local rise in water level here. The provided applications of a method show what dynamic component of pressure can modify considerably structure of currents on elements of the hydraulic engineering constructions.

Translated by E.S. Kochetkova

Based on the data of numerical simulations of the wind wave parameters, the wave energy resources of the Baltic Sea were estimated. Calculations of the wave parameters were performed using the SWAN spectral model and the wind data of NCEP/CFSR (CFS2) reanalysis from 1979 to 2015. The simulations were realised using a rectangular grid with a spatial resolution of 0.05°. The maps of the average annual wave energy flux for the period 1979–2015 were plotted. The maximum values of which reach 6–6.5 kW/m and appear in the Baltic Proper and in the South-Eastern Baltic. For the Kaliningrad Region, the wave energy flux is 3–4 kW/m. The analysis of the seasonal and interannual variability of the wave energy flux for two points located in the open sea and in the coastal zone of the South-Eastern Baltic was carried out. Seasonal variability of the wave energy flux is very high: the energy flux in the winter months is several times greater than in the summer period. The average long-term probability of exceedance of the wave energy for several thresholds was calculated. The probability of exceedance of the wave energy with a threshold 1 kW/m in the Baltic Proper is 55–60%.

Measurements performed by a loosely tethered free-falling microstructure profiler in the vicinity of the Słupsk Sill revealed a high turbulence dissipation spot immediately beyond the sill to the east in the near-bottom layer filled with eastward spreading saltwater. An approach is developed to quantitatively estimate the role of a topographic obstacle like the Słupsk Sill in mixing/transformation of inflow waters using data of microstructure measurements. To do this, first, based on vertical profiles of specific dissipation rate of kinetic energy of turbulence and potential density, the rate of entrainment of low salinity water from the overlying layer to the near-bottom turbulent saltwater layer is calculated. Then, assuming that in the near-bottom saltwater flow, the critical value of the Froude number is reached directly at the Sill, the flow volume rate is estimated. Finally, from the balance between advection and turbulent entrainment, the change in salinity of the eastward spreading saltwater due to intensification of mixing at the Sill can be evaluated. Using data of microstructure measurements available, the mixing hot spot at the Słupsk Sill was found to be responsible for approximately 5 percent of the inflow water salinity decrease en route from the Arkona Basin to the Gotland Deep.

Setting nutrient load reduction targets for the Baltic Sea, and monitoring whether these targets have been met, calls for reliable information on the nutrient load from all the surrounding countries. The objective of this study was to estimate the loading of N_tot and P_tot from the Russian territory on the Gulf of Finland, one of the most eutrophied subbasins of the Baltic Sea. The nutrient load assessment was based on available monitoring data and statistics, mathematical modelling and additional sampling in the previously unmonitored areas. New data on nutrient loads at the small unmonitored rivers of the Gulf of Finland immediate catchment are presented and discussed. The data compilation showed that in order to fulfil the nutrient abatement recommendations of the HELCOM Baltic Sea Action Plan for the Gulf of Finland, a further reduction of 2084 t of N/a and 202 t of P/a from Russia is needed. Suggestions to improve Russian load monitoring system are given.

This paper reviews physical mechanisms of formation for informative features of acoustic target echo induced by elastic characteristics of the object’s material. It is demonstrated that a probing acoustic signal causes forced and selfinduced vibrations of various kinds in the investigated object (including on frequencies unconnected with exposure rate). The vibrations have sufficient amplitude and cause secondary stimulated emission that is added to the main reflection, and as a result of interference there appears an ultimate modulated signal carrying information on the object’s material. The main classification features that allow identifying the object’s material are: surge resistance, surface acoustic wave speed, frequency and damping ratio of natural resonant vibrations.

To improve the returned signal’s informative features, especially for identifying small-sized objects, it is required to optimize the characteristics of transducing devices in a particular direction, including the characteristics of transducing antennas. Moreover, probing signal parameters and reflected signal processing algorithms need to be optimized.

Analysis of the influence of ultralow frequency (up to 0.05 Hz) fluctuations of sea vessel underwater noise emission on the possibility of extraction of signal amplitude modulation existing in the frequency band of sea vessel rolling and pitching on the rough surface (from 0.03 to 0.5 Hz) is carried out. Possible characteristic variants of ultralow frequency fluctuations spectra are determined based on the analysis of signals recorded in natural conditions. Appearance of ultralow frequency signal fluctuations was observed in different frequency bands of the total frequency band of the carrier signal (from 0.5 to 8.0 kHz). Different hypotheses of the nature of ultralow frequency fluctuations formation depending on hydrologicalacoustic conditions are proposed. It is shown that ultralow frequency fluctuations can have negative effect on the possibility of amplitude modulation detection. Possible circuits of extraction of signal amplitude modulation in rolling and pitching frequency band against ultralow frequency fluctuations are considered. The effective method of compensation of ultralow frequency fluctuations influence for a standard device of detection of amplitude modulation caused by rolling and pitching is presented. The proposed method is implemented as software in the structure of a standard device. Operability of the method has been shown using noise signals of sea vessels recorded in natural conditions.

The joint object recognition and distance determination are considered by comparing the spectral pressure density of the noise signal observed at a certain object distance, with the samples of the spectral pressure density of the noise signals of the objects stored in the database. The solution of the problem is based on minimization of the measure of proximity between the detected signal and the samples stored in the database of signal spectra. The article analyzes the main known methods of distance estimation at the passive detection sonar, and carries out a comparative analysis of various proximity measures to solve recognition problems and estimate the distance of a detected marine object. The most characteristic measures reflecting the specifics of different types of distances were considered: similarities and distances for numerical data (Ruzhechka, Bray–Curtis, Canberra, Kulczinski), analogs of Euclidean distance (Euclidean distance, Manhattan distance, Penrose size distance, Penrose form distance, Lorentzian distance, Hellinger distance, Minkowski distance, Mahalanobis distance or statistical distance), correlation similarities and distances (correlation similarity, cosine similarity). Low efficiency of metrics of correlation and cosine and expediency of use for the problem decision such metrics, as analogues Euclidean distance, is shown. It is shown that the values of these metrics are the functions of the signal level of the object, which determines the need to compare the measured signal and the samples of the database of signal spectra for different noise levels. The perspective directions of further researches are defined.

The study presents results of the development of the technology of airborne for calculations the number of population of harp seals (the White Sea population as example) by using satellite passive microwave survey that allow to select the “hot spot” zones — ice area where mass accumulation of ice-associated marine mammals at the season of mass-whelping should be most possible. Selection of these zones allows rise the efficiency and reduce the costs of airborne survey. Some examples of field observations that were fulfilled onboard of the research aircrafts PINRO Antonov-26 “Arktika” and NII GIPRO Rybflot L-410 “Nord” are also shown.

We consider the works of K.S. Shifrin devoted to development and applications of the rigid and approximate methods to solve the problem of light scattering by small particles. We discuss the impact of his book “Scattering of light in a turbid medium” and five volumes of “Tables of light scattering”. We note his papers on light scattering by very large and very small particles, particles with the refractive index m close to 1, core-mantle particles and particles with m continuously changing along the radius, as well as some other papers related to solution of the direct tasks in light scattering.

Multy-spectral passive microwave sensors are placed at present practically in each satellite that realizes the geoecological investigations of the Earth. The paper describes the history of creation of the remote sensing methodology in microwaves from the beginning when the theoretical justification of the possibility revealing of the parameters of the system “Earth–atmosphere” was done in 1960-s by professor Kusiel Schifrin – the leading scientist of the Voeikov Main Geophysical Observatory till nova days when different dangerous and ecologically significant parameters of the land and seas could be retrieved by using satellite microwave survey.