The influence of different versions of the planetary boundary layer parameterization in the model of system “Wave – Atmosphere” on the quality of wind wave simulation is investigated. The system consisting of components: WAVEWATCH (wave) / WRF (atmosphere) adapted for the Baltic Sea is described. The schemes of the planetary boundary layer parameterization used in the WRF are considered. From all experiments are selected two cases with stormy conditions observed in 2014: from 11 to 20 August and from 4 to 10 October. The comparison is produced by root-mean-square error of significant wave height simulation calculated according to automated FMI buoys located in Northern Baltic Proper, Bothnian Sea, Bay of Bothnia, Gulf of Finland. The sensitivity of significant wave height reproduction to different ways to PBL is evaluated. The evolution of storm waves at each buoy point is considered. The selection of parameterization with less errors in wind wave simulation is justified.

Sea state forecast in operational oceanology is based on numerical models, which in most cases employ hydrostatic approximation, and therefore require the reconstruction of full hydrostatic pressure by using available measurement data. The sea level dynamics associated with density field heterogeneity may be taken into account by assimilation of thermohaline measurements, which leaves only the problem of estimating the barotropic pressure component. In particular, the barotropic part of pressure may be obtained by using satellite altimetry data. However, such data may contain large errors, especially for Arctic region or marginal seas, or bluntly may be unavailable. We discuss the problem of the reconstruction of the barotropic component of the hydrostatic pressure based on velocity measurements. It is shown that if the hydrostatic approximation is used, then the near bottom surface pressure may be estimated using the measurements of velocity near the ocean bed. Numerical simulations of wind driven barotropic ocean were performed. Calculations confirm that the reconstruction of barotropic component of hydrostatic pressure may be performed with sufficient accuracy for operational oceanology.

One of the problems of operational tsunami forecasting is a large (more than 75%) number of false alarms. According to modern ideas, tsunami warning services should declare not only reasonable general alarms, but also differentiated by the degree of danger for specific areas of the coast. A tsunami warning should be issued with a reasonable advance warning only at points where a tsunami poses a real threat, and should be accompanied by information on the arrival time of the first, maximum waves, their amplitudes, as well as the expected time of the end of the tsunami. Tsunami forecasting that meets these requirements is possible using tsunami information obtained in the open ocean from sea level measurement stations. In the case of local tsunamis, ocean level measurement stations located near the focus contain noise of seismic origin superimposed on the useful tsunami signal, which can make it difficult to obtain an adequate forecast.

The results of numerical simulation of the process of operational forecasting of local tsunamis of 2006 and 2007 on the Kuril Islands according to the data of the closest to the islands deep-ocean level station are presented. The computation was performed according to the station data complicated by seismic interference. The principal possibility of operational forecast of tsunamis arising at the Central Kuril Islands, according to the data of closest to the centers level station, even in the presence of seismic noise, is shown. Advance forecast for settlements of the Northern and Southern Kuril Islands is 0.5—1.5 hours, which ensures timely submission of alarm and evacuation of the population to safe places.

A numerical simulation of the evolution of tsunami waves in the Azov-Black Sea basin was carried out for 10 elliptical foci, which corresponded to the already existing tsunami by underwater earthquakes. The time of the wave propagation to the coast of the Black and Azov Seas is calculated. It is from a few minutes for the nearest to the tsunami focus coastal regions to 4.5 hours for Odessa coast. The maximum sea level elevations along the coast of the Black and Azov Seas caused by the propagation of tsunami waves from zones of local earthquakes were obtained. The most dangerous coastal zones are identified. The sea level increase along the coast during the propagation of tsunami waves caused by earthquakes with magnitude about 7 reaches from tens of centimeters to more than 1 m. The changes of the amplitude characteristics of tsunami waves from the earthquake magnitude and the location of sources tsunami are shown. The displacement of the local tsunami focus to the deep part of the sea leads to growth of the amplitude of the level oscillations near the coast. The increase of the earthquake magnitude results in amplification of the sea level fluctuations, which may exceed the height of the initial perturbation.

To study the propagation characteristics of microplastic particles coming with the Neva river waters, in the Neva Bay and in the eastern part of the Gulf of Finland, a three-dimensional numerical hydrodynamic model based on the Princeton Ocean Model is used. The model is implemented on a uniform quasi-orthogonal horizontal grid with a step of 100 m, in the vertical direction 7 uniformly distributed sigma levels are used. The marine initial conditions and conditions at the western boundary for water level, temperature and salinity were taken from the Baltic Sea operational model HIROMB-BOOS of the Danish Meteorological Institute with discreteness of 1 hour. On the eastern boundary at the mouth of the Neva the average monthly climatic river discharge and temperature of the Neva were set. Atmospheric forcing was taken from the results of the ECMWF ERA-Interim reanalysis with 6-hour temporal resolution and with a spatial resolution of 0.125 × 0.125°. Two types of suspension were considered that simulated the propagation of microplastic particles in the water: admixture of neutral buoyancy and a sinking suspension with a sinking velocity of 0.2 m/day. Both types of suspension come from the Neva River with a constant volume concentration of 10−6. To calculate the thickness of the layer of the settling fraction at the bottom the simplified Exner equation is used. The calculations were performed for the period May—August 2018 when the quantity and composition of plastic litter was monitored on the coast of the Neva Bay and the eastern part of the Gulf of Finland.

According to model results, the spatial distribution of the sinking particles, in general, repeats the distribution of the admixture of neutral buoyancy, with the only difference being that the farther from the particle source to the west, the lower the concentration of the sinking particles. An essential feature of the distribution is that during most time of the considered period the concentrations of both suspensions in the northern part of the model domain is higher than those found in its southern part. The change in the thickness of the bottom layer of the particles of the settling fraction at the end of the period on August 31, 2018, i.e. the accumulation of microplastic particles in bottom sediments for the period under consideration, is characterized by the same feature as the space distribution of the admixture of neutral buoyancy in water: the accumulation of microplastic in bottom sediments in the northern part of the model area outside the Neva Bay was noticeably greater than in the southern part, especially in the coastal zone.

The data on monitoring the coastal pollution by plastic litter indirectly confirm the model results: there was practically no plastic litter on the southern coast of the eastern Gulf of Finland outside the Neva Bay between June and August 2018, while it was found on the northern coast in significant quantities. Thus, model estimates of the distribution of microplastic particles in water and its accumulation in bottom sediments can be used to select areas for future work on monitoring plastic litter pollution on the coast of the Gulf of Finland.

The study is aimed to present data on prevailing directions, variability and magnitude of currents within the investigation of the Black Sea circulation at the depth below Statistical pycnocline. Vertical profiles of the velocity were obtained from the in-situ measurements during expeditions of the Marine Hydrophysical Institute. Among these data, 25 locations were selected where measurements are available from 500 m deep and below. The measurement equipment and geographical locations of the stations are provided. Periods of surveys took from hours to 2 months. Data availability both in time and space was sufficiently uneven, however present study for the first time renders full measurements array since 1960-s.

After data quality assessment and projection to 500, 750 and 1000 m horizons, a table was built, which demonstrates the data coverage, direction frequency along with the average current speed.

The analysis of vertical profiles demonstrated that current velocity vectors at some stations in the near-surface and deep layers have similar directions. However the majority of the examined profiles show velocity directions that differ significantly between the horizons. For each stations and horizons directional rose-charts for velocities and absolute values were plotted. Those were used for illustration of the cases of current velocity switch between different layers. The absolute value of a velocity vector deeper than 500 m might be greater than the value in the upper layers.

Currently application of hydroacoustic systems, which detect and estimate parameters of underwater sources of sound, still remain the main method of underwater state coverage. We consider native basic processing of hydroacoustic fields, including a procedure which takes sea state into account and gives an estimate of signal likelihood ratio in each point of overview area. An example of the implementation of native processing based on ray model for the case of experimentally detected signals on horizontally towed antenna with 48 receivers and a length of 100 meters is given. During processing almost all available information on sea state and distortions is used. It is shown that the effectiveness of hydroacoustic systems may be significantly increased if the distortion of signal in heterogeneous fluid is taken into account.

Algorithms for calculation of signals and distortions, detection and estimation of the range of hydroacoustic systems in passive mode have been implemented in numerical models. A comparison with traditionally used processing method in case of linear antenna model with 128 receivers with a total length of 512 meters is performed. Native basic processing solves the problems of detection, classification and coordinates estimation. Such processing may well be implemented by modern means considering the scope of available hydrophysical and hydroacoustical data.

Analytic dependences determining the propagation-related laws of attenuation of the sound pressure of low-frequency signals formed in a waveguide in zones of interference maxima are obtained and investigated. As applied to the Pekeris waveguide and a non-directional monopole source, convenient approximating expressions are found that are in good agreement with the exact laws of the drop in the pressure field in these zones.

The paper presents the generalized results of studies of the water surface layer bio-optical characteristics of the Barents, Kara and Laptev Seas and the interpretation of the observed phenomena. A joint analysis of the data on the bio-optical characteristics spatial distribution obtained in 2018 using a shipboard flow-through measuring complex and satellite observations for the period 2003—2017 was performed. The analysis allowed us to identify the role of the main processes that determine this distribution, its seasonal and interannual changes. It is shown that the spatial distribution of the fluorescence intensity of the colored dissolved organic matter and chlorophyll is in good agreement with the hydrophysical characteristics in the area of river runoff influence; the spatial distributions of the attenuation coefficient are in good agreement with them. The data obtained made it possible to determine the position of the Arctic and Atlantic waters and coccolithophore blooms in the Barents Sea, to identify the distribution boundaries of the surface desalinated layer in the Kara and Laptev Seas. Statistical estimates of the relationship between the bio-optical characteristics of the Barents and Kara Seas from satellite data are presented.

The characteristics of a light pulse propagating in water modulated by a radio signal with a frequency varying linearly with time are investigated. The analysis is based on statistical modeling of the pulse and frequency characteristics of the signal and the analytical representation of the signal as a pulsedescribed by a Gaussian function with intrapulse modulation. Changes in the arrival time and the pulse envelope duration caused by the photon pathlength dispersion at distances between the source and receiver up to four white disk visibility depths are estimated. It is shown that these changes may have different signs depending on the modulation frequency range . A comparison was made between arrival times and durations of the pulse with a time-varying frequency and the pulse after matched processing consisting in convolution with the original modulating signal. It is shown that in the investigated range of parameter changes, multiple scattering does not prevent the compression of a complex signal when it is matched processing.

A compensatory approach aimed at eliminating methodological errors in the measurements of the beam attenuation coefficient in seawater is proposed and the scheme of the transmissometer in which this approach is implemented is described. The special feature of the proposed optical scheme is that the measuring and reference beams are formed by identical optical elements that make up the reference and measuring channels, while both channels are transmitted to the measured medium. Since the measurement and reference channels are identical and both are transmitted in the measured environment, there is no need to correct changes of reflectance on optical parts when the device is immersed in sea water. There is also no need for complex calibration using pure water. As a result, it is possible to use the instrument calibration in air to determine the beam attenuation coefficient after immersion of the instrument in water. Since the measurements are actually performed on two optical bases, self-calibration of the device can be performed without the usage of pure water with known optical characteristics. A powerful multi-element seven-color LED is used as a light source.

Airborne lidar bathymetry survey of Bechevinsky Bay is distinguished by difficult flight conditions (the narrow bay is surrounded by high hills). The flight altitude of the aircraft during survey varied within the range of 500 to 1200 m. The survey was performed using the Airborne Polarization Lidar APL-3 (probe pulse energy is 40 mJ, duration of probe pulse 7 ns, diameter of the receiving optical system is 100 mm). The maximum depth of sounding of the bottom from altitude of 500 m was 21.5 m, from altitude of 1200 m – 17.5 m. The energy of the probe pulse required to obtain bottom return from different altitudes is estimated. It is necessary to increase the pulse energy by 20 times to locate the bottom of 25 m depth from a safe for flying altitude of 2500 m. An increase of survey flight altitude from 200 m to 2500 m under these conditions for obtain bottom return at a depth of 25 m requires a 150-fold increase of the pulse energy.

There is a version about the constructing of the tide-gauge «on walls» of Peter and Paul fortress after Neva flood in 1715. But the foundation of this version is the brief fragment from I.G. Georgi’s opus (1790). It isn’t clear from the translation of original text what fortress is mentioned – Peter and Paul or Admiralty. At first sight this text can be associated only with «Peter and Paul version». But impossibility of finding references of sources which can verify the existence of first Russian tide-gauge near Peter and Paul fortress from 1715 (by decree of Peter I) and inconsistency of these statements with wellknown facts are the reason not to formulate precipitate conclusion.

Many facts confirm «Admiralty version»: establishing of department – prototype of «Admiralteistv-College» (with functions of level monitoring); provision of safety launching of vessels; special attention of Peter I to marine attributes (foreign experience implied tide-gauges in ports). Besides no one document which verifies the organization of first instrumental researches of natural environment in Russia and which dates earlier than I.G. Georgi’s opus contains mentions of the Peter and Paul tide-gauge.