Methodological and technical possibilities of monitoring temperature fields along a 1000-km track in the Sea of Japan using acoustic thermometry are presented. The proposed tomographic method for monitoring the dynamics and structure of waters is based on emission and reception of complex phase-shift keyed signals on a diagnosed path with determination of the propagation time along various ray trajectories with further measurement of the speed of sound and temperature. The physical prerequisites for practical use of thermometric studies at large distances are based on the acoustic “mudslide” effect: the phenomenon of the transition of acoustic energy from the bottom shelf area to an underwater sound signal of the deep ocean. A high-precision system of acoustic thermometry on the basis of tomographic schemes with mobile and stationary hydroacoustic emitters and receiving systems is proposed and tested with the example of the Sea of Japan.

This paper presents a technique for estimating the Doppler frequency shift of the probing signal. The technique is based on the use of a signal packet consisting of at least two identical complex signals with “good” autocorrelation properties, and the operation of autocorrelation (“convolution” of the received signal with itself) at the receiver. The results of experimental testing of the technique, carried out on August 17, 2013, are presented. The obtained field data are compared with GPS measurements and algorithms for estimating the Doppler shift.

—The results of studies of the features of the formation of pulse characteristics on the axis of an underwater sound channel in waveguides with different hydrological and bathymetric conditions of the Sea of Japan and the Sea of Okhotsk are discussed. The results of model calculations and experiments characterizing the regularities of propagation of low-frequency pulse signals in complex waveguides including shelf and deep sea for hundreds of kilometers are presented. It is shown that one of the main effects that determines long-range sound propagation in complex waveguides including the shelf and deep sea is the acoustic “landslide” effect. It is also shown that numerical modeling of the process of signal propagation from the shelf to the deep sea on acoustic traces in the Sea of Japan and the Sea of Okhotsk using the RAY program provides good convergence of the calculated and experimentally obtained impulse characteristics.

The methodological and technical possibilities of monitoring temperature fields in the Sea of Japan by acoustic thermometry methods are presented. The proposed tomographic method for monitoring the dynamics and structure of water is based on the transmission and reception of complex phase-shift keyed acoustic signals on a diagnosed track with the determination of the travel time along various ray trajectories, followed by the sound speed (temperature) determination. The physical prerequisites for the practical implementation of thermometric studies at large distances are based on the acoustic “mudslide” effect—the phenomenon of the acoustic energy “injection“ from the near-bottom shelf area to the underwater sound channel of the deep ocean. Based on the Sea of Japan example, an acoustic thermometry system based on tomographic schemes with mobile and stationary hydroacoustic sources for promising work in the field of oceanic climatology is proposed. For numerical calculations of the signal propagation channels’ impulse responses between sources and receivers, a specialized database of oceanological information was formed for the northwestern part of the Sea of Japan. The database includes all available data from organizations in Russia, Japan, North Korea, the Republic of Korea, and the United States (23,247 stations completed from 1925 to 2017). In the example of the Sea of Japan, a high-precision acoustic thermometry system based on tomographic schemes with developed mobile and stationary hydroacoustic transmitting and receiving systems was proposed and experimentally tested.

Приведены результаты экспериментальных и теоретических исследований по распространению и приему в подводных звуковых каналах широкополосных импульсных сигналов на основе псевдослучайных последовательностей. Анализ экспериментально полученных импульсных характеристик указывает на наличие предпосылок для повышения помехоустойчивости приема навигационных и командных сигналов, а также увеличения дальности действия при неизменной мощности излучения. Цель специально выполненных экспериментальных работ заключалась в получении исходных данных для повышения эффективности навигационных систем дальнего радиуса действия путем оптимизации характеристик излучаемых сигналов. Исследованы особенности формирования импульсных откликов при приеме сигналов с различной частотной полосой и длительностью символов, а также динамика структуры откликов при смещениях глубины приёмного гидрофона относительно оси подводных звуковых каналов. На основе лучевых представлений осуществлена физическая интерпретация полученных экспериментальных результатов для практического применения в решении актуальных задач гидроакустики и океанологии.

The results of experimental studies on the features of propagation and reception of broadband pulsed signals in an underwater sound channel (USC) at a distance of 300 km from the source are discussed. The characteristics of the formation of the pulse responses by reception of the phase-shift keyed signals with different frequency bands and durations of symbols are studied. From the point of view of the ray theory of sound propagation in a deep-ocean waveguide, a physical interpretation of the results is presented and practical conclusions are drawn for solving the problems of positioning of autonomous underwater platforms.

The results of experimental and theoretical studies on the propagation and reception of broadband pulsed signals based on pseudorandom sequences are discussed. The features of impulse response functions for reception of signals with different frequency bands and durations of symbols are investigated. Separation of acoustic energy arrivals in the cross-correlation function of the received and emitted signals is investigated in the framework of the normal mode theory for a deep-sea waveguides. The study concluded that a combination of navigation signals with different symbols duration must be used for solving practical problems of autonomous underwater vehicles positioning.

An experimental study aimed at the measurement of arrival times and effective velocities of acoustical pulses propagating approximately along the edge of the continental shelf was conducted in the Sea of Japan in early autumn. In a posteriori theoretical analysis and modeling of sound propagation in this experiment modal structure of acoustical field along the path was described and a number of general conclusions on the formation of such fields in course of sound propagation over distances of tens and hundreds of kilometers were formulated. An algorithm for predicting effective velocities of long-range propagation of acoustical pulses in shallow water was developed on the basis of these conclusions. The algorithm is based on the averaging of group velocities of the first modal component of the pulse over the entire track. It was shown that on the considered path of approximately 136 kilometers horizontal refraction is one of the major factors contributing to the dispersion of pulsed signals. This effect also causes additional delays as compared to the sound propagation along the respective geodesic path on the Earth’s surface. Implications of the importance of taking the horizontal refraction into account in estimation of arrival times in the modeling of long-range propagation and the solution of acoustical ranging problems are also discussed.

Применение фазоманипулированных сигналов на базе последовательностей с исключительными корреляционными свойствами является одним из ключевых методов решения практических задач в подводной навигации, связи и томографии. В статье обсуждаются результаты исследований по распространению и приему широкополосных импульсных сигналов на основе псевдослучайных М-последовательностей. Исследованы особенности формирования импульсных откликов при приеме сигналов с различной частотной полосой и длительностью символов. Сделан практический вывод о необходимости комплексного применения различных по длительности символов навигационных сигналов при решении задач позиционирования автономных подводных аппаратов. Utilization of phase-shift keyed signals based on sequences of outstanding correlation properties is one of the critical methods for solving the practical tasks in underwater navigation, communication, and tomography. The present work considers the results of experimental research on the propagation and reception of wideband impulse signals based on pseudorandom M-sequences. Throughout the experiments, the features of impulse response formation were investigated when receiving signals of different frequency bands and duration. The results of theoretical and experimental research suggest practical reasoning of the necessity of complex usage of navigational signals of different duration when solving the tasks of the autonomous underwater vehicle positioning.

A hydroacoustic autonomous receiving system that uses a combined receiver has been developed for carrying out investigations of the vector−scalar structure of acoustic fields under shallow water conditions with a submersion depth as large as 100 m. The acoustic fields are investigated by measuring the acoustic pressure and three orthogonal components of oscillatory acceleration using sensors with a sensitivity of 150−180 μV/Pa. In addition, data on the spatial position of the system from the orientation and depth sensors are synchronously recorded and, together with the data from acoustic channels, are saved to an SD card.

The article discusses the results of experiments conducted in September 2017 to prove the applicability of positioning underwater objects during their operation at depths substantially exceeding the depth of the underwater sound channel axis. The authors present results of experimental studies and numerical analysis of the effect of focusing of the acoustic energy in the near-bottom layer on the shelf and its transition into deep-water (up to 500 m) layers of the Sea of Japan for summer–autumn hydrological conditions. Experiments on reception of broadband pulsed signals with a center frequency of 400 Hz were carried out at various distances (20, 68, 86, 90, and 198 km) from a source of navigation signals moored at a depth of 35 m at the shoreline near Cape Schulz. The receiving of acoustic signals was performed by a system of distributed over depth up to 500 meters hydrophones, with the possibility of long-term signal recording at fixed depths and during submergence. The experimental results allowed to study the impulse responses of acoustic waveguides, and estimate the effective propagation velocities of navigation signals received at different depths, and to draw conclusions about the possibility of solving positioning problems for autonomous underwater vehicles at depths up to 500 m and distances up to 200 km from the source of navigation signals. Mathematical modeling of acoustic wave propagation in a waveguide reproducing the experimental conditions by the normal mode technique was also carried out.

A family of configuration spaces in the description of the internal dynamics of a rigid molecule has been considered. It has been shown that the requirement of the physical correctness of the description leads to serious restrictions for such spaces. In particular, only spaces satisfying the Eckart condition are allowed for a nonlinear rigid molecule.

The results of experimental study of the spatial structure of the scalar-vector acoustic field formed during towing of a tone low-frequency emitter over the shelf of the Sea of Japan are discussed. The experiment was accomplished by towing the source of a tone signal with a frequency of 134 Hz at a depth of 20 m over various acoustic tracks at distances up to 10 km from an integrated receiving system consisting of a receiver of acoustic pressure and three orthogonal components of the acoustic pressure gradient. Special attention has been focused on study of the interference structure of the scalar and vector fields with provision of the technical reliability of the method and the results of the experiment under controlled hydrological conditions. We discuss the quantitative characteristics and peculiarities of the interference formation along tracks that differ in depth. The unique results of comparing the horizontal and vertical components of the fields are most interesting of all. They allowed us to reveal the existence of eddy structures in the acoustic field of the source over several tracks. We analyze the possibility of practical application of the results of our research.