The knowledge of salinity in a specific sea area with high accuracy is required to solve several acoustic and hydrophysical problems on the ocean shelf. Unlike temperature, which can be measured continuously for a long time, with, for example, thermistor strings (thermostrings), salinity values of required accuracy can be obtained only using CTD profiling. This is why methods of estimating salinity from temperature could be helpful. In this paper, the authors propose using the regression method for solving this type of problem and demonstrate the efficiency of this method using examples of temperature measurements from anchored thermostrings. For the correct construction of regressions, the authors analyzed the errors of CTD measurements and suggested a method for the dynamic correction of raw CTD data. From CTD profiling datasets of 12 years (2011–2022), after their dynamic correction, the authors obtained regression polynomial formulas for calculating salinity from temperature and studied data stability in space and time at the hydrophysical test site, located in the shelf zone of the Sea of Japan. The authors consider this method efficient and applicable in solving a variety of acoustic and hydrophysical problems.

We describe the design of a hydroacoustic emitting station with an electromagnetic transducer that develops acoustic pressure of up to 2400 Pa (188 dB) reduced to a distance of 1 m from the emitter axis in a frequency range of 420–520 Hz (at the level of –3 dB); it has an operating depth of up to 500 m. The applied technical solutions make it possible to use the station for a wide range of oceanological research, as well as for the construction of navigation systems for underwater vehicles and data transmission via a hydroacoustic channel.

This paper presents a discussion on observations of nonlinear internal waves (NLIWs) in the coastal zone of the Sea of Japan, based on the mooring of thermostring clusters in different seasons of 2022. For statistical evaluation of the frequency of event occurrence and determination of NLIW movement direction, we use our observations of the past 12 years. We present the NLIW structures, observed in spring, summer, and autumn of 2022, which are typical for this shelf area. Two types of nonlinear waves are described—solitary and undular bores, with or without strong vertical mixing behind the front. We demonstrate spatial transformation of an undular bore as it moves over the shelf. A mathematical model based on the second-order shallow water approximation is proposed for numerical simulation. To simplify calculations, the authors limit themselves to two- and three-layer shallow water models. We investigate the possibility of spatiotemporal reconstruction of internal nonlinear structures between thermostrings using experimental data and proposed models. The authors show that at distances of up to several kilometers between thermostrings, the wave fields of strongly nonlinear and nonstationary structures can be successfully reconstructed. Water flow induced by NLIWs can be reconstructed from the data of even one thermostring.

New data were obtained on the formation mechanisms of relief sediment waves (SWs) in Peter the Great Bay of the Sea of Japan. From the studies, we can assume that the sediment waves in the bay originate from two types of turbidity (TB) currents: (1) fine-dispersed TB currents caused by disintegrating internal waves and entrained by the Primorsky current along the shelf through SWs troughs; (2) fine- and coarse-grained TB currents, formed and entrained by the Primorsky current, intensified by the typhoons. This work presents the geological structure of the shelf area containing SWs. We established that the area of SWs location is on the border of change in facies conditions of sediment bedding in the bay. The transition from the inner shelf facies to the outer shelf facies occurs at a depth of 50–60 m. We analyzed the space variability of temperature and sound speed fields peculiar to the region on the results of hydrological CTD measurements and long-term measurements with moored vertical thermostrings. In the course of measurements, seven typhoons during their passage off the Primorye coast of the Russian Federation were registered. We found a significant change in the hydrological situation in the bay under the influence of extreme external factors. Under calm meteorological conditions, up to three mild thermoclines were observed in the bay, located at depths of 8–15 m, 30–35 m, and 45–60 m. During the passage of typhoons, they combined into one powerful thermocline at a depth of approximately 50–60 m, and in some cases, a high-gradient thermocline formed at the depths of 30–40 m (about 12–15 °C per 10 m of depth). The high-gradient layer significantly increases the amplitude and strength of internal gravity waves, thereby increasing the speed of currents in the water media. We should note that this period of transformation of the hydrological profile on the shelf under the influence of typhoons covers the period from August to October-November. We established that in the SWs location area, firstly, the process of internal waves disintegration intensifies in the autumn season, resulting in the formation of the waves with lengths close to the SWs horizontal scales (SWs wavelengths); secondly, under the influence of the typhoons entering the Sea of Japan, the kinetic energy of the shelf branch of the Primorsky current increases. In this case, it acts as a source of TB currents, including medium- and coarse-grained sedimentary material that forms SWs.

This paper describes the design solutions and characteristics of autonomous acoustic loggers and a brief description of the elements of the measuring hydrophysical complex (acoustic emitters, thermal strings, etc.), in which they are used. The technical capabilities of acoustic loggers allow one to quickly create various configurations of discrete antenna arrays and acoustic interferometers. Based on the data that are obtained from such receiving systems as parts of a hydrophysical complex it is possible to diagnose the water environment and bottom sediments, as well as evaluate the acoustic characteristics of various sound sources. Some methods and approaches for solving such problems are proposed and examples are presented.

Для решения прямых и обратных задач практической гидроакустики необходимо иметь наборы статистических феноменологических моделей пространственно-временных вариаций скорости звука. Как правило, такие возмущения определяются внутренними гравитационными волнами (ВГВ), что делает актуальной проблему разработки их адекватных статистических моделей. В данной работе на основе результатов обработки экспериментальных данных проанализированы характеристики высокочастотной (превышающей 2,5 цикл/ч) составляющей фоновых ВГВ. Натурные наблюдения проводились авторами на шельфе в юго-западной части залива Петра Великого Японского моря в весенний, летний и осенний сезоны на протяжении последнего десятка лет. Проделанный анализ наиболее интенсивных изотерм демонстрирует, что с достаточной точностью флуктуации температуры можно считать гауссовыми. Это позволило авторам разработать и применить методику рандомизации спектрального представления случайного поля (ковариационной матрицы ВГВ) для построения статистической рандомизированной модели, из которой можно выбирать отдельные статистические реализации поля ВГВ для решения конкретных прикладных задач гидроакустики, связанных в том числе и с разработкой судовой аппаратуры для подводной связи, навигации и обнаружения подводных и надводных источников звука. To solve both direct and inverse problems of practical hydroacoustics, one needs a set of statistical phenomenological models of spatiotemporal variations of sound speed. As a rule, such variations are determined by internal gravity waves (IGW), which makes the problem of developing adequate statistical models of IGW a pending issue. In this paper, based on results of the experimental data processing, the characteristics of high-frequency (exceeding 2.5 cycles/h) component of the background IGW are analyzed. Field observations were carried out by the authors on the shelf in the southwestern part of Peter the Great Bay of the Sea of Japan in spring, summer, and autumn seasons over the past ten years. Analysis of the most intense isotherms demonstrates that the temperature variations can be considered Gaussian with sufficient accuracy. This fact allowed the authors to develop and apply a randomization technique for the spectral representation of a random field (the IGW covariance matrix) to construct a randomized statistical model from which it is possible to select some statistical implementations of the IGW field for solving specific applied problems of hydroacoustics.