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.

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.

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.

The aim of the study whose results are discussed in this paper was to conduct experimental and numerical research on improving a high-accuracy method, developed by the authors, of positioning underwater objects. For this, experimental testing of an improved range-finding technology was carried out, based on the inclusion into the measuring scheme of a block that can measure and monitor the sound velocity on the shelf area of a track connecting a source of navigation signals and an a receiver system imitator consisting of autonomous underwater apparatus. In addition, under natural conditions, we implemented a scenario in which range-finding data was provided to an autonomous underwater apparatus carrying out a mission in the water area at a distance of 300 km from the source of navigation signals using technical tools for controlling variability of the sound velocity on the shelf. A specific example was used to test the acoustic range-finding technology on a track with complex hydrological and bathymetric conditions, and an estimate was obtained for the accuracy of measuring distances during a 4 h drift of the autonomous underwater apparatus imitator.

The paper examines how hydrological conditions affect manifestation of the acoustic “landslide” effect, which consists in focusing of acoustic energy in the near-bottom layer on the shelf and its transition to the axis of an underwater sound channel in deep water. We compare the results of experiments performed in the Sea of Japan in April 2014 and August 2006 on the same acoustic track, where the distance between corresponding points was more than 100 km. In April, the hydrological conditions in the shelf region of the track and in the upper layer of the deep-water part of the sea were characterized by the presence of a relatively weak (~0.35 s –1 ) negative vertical sound velocity gradient, whereas in August 2006, it was ~1.5 s –1 . Experimental and numerical studies showed that the acoustic landslide effect also manifests itself under conditions of a weak negative sound velocity gradient, but the structure of the acoustic field trapped by the underwater sound channel has a more complex character with a time-expanded pulse characteristic. Nevertheless, its ordered, stable, and well-identified structure at all track points chosen for measurements make it possible to reliably create an efficient (with accuracies to hundredths of a percent) underwater navigation systems like GLONASS and GPS for the spring hydrology season.

A measuring complex has been designed for experimental investigations of the effects that hydrophysical processes in a marine environment have on the quality of navigation using on-board equipment of submersibles in the process of signal reception from hydroacoustic beacons installed near the shoreline. The main systems and characteristics of the measuring complex are described.

A hardware and software system for measuring the angular structure of acoustic fields using the vector-phase methods for processing the complex M-sequence probing signals is described. The results of testing the system are given. A unique relationship between the change in the temperature condition on the stationary acoustic route and the times and angles of arrival of the acoustic energy is determined under controlled hydrological conditions. It is shown that, using vector receivers in tomographic schemes, it is possible to obtain an independent additional parameter of the pulse response of the diagnosed waveguide and increase thereby the efficiency of reconstruction of hydrophysical fields from acoustic probing data.

Results of experimental studies of the field of currents in the shelf zone of the Sea of Japan are discussed. The studies were carried out in 2001–2002 near the Gamov Peninsula, in the region of the acoustical-hydrophysical site of the Il’ichev Pacific Oceanological Institute (Far East Division, Russian Academy of Sciences). The purpose of the studies was related to the problems of developing the systems for long-term remote sensing of the climatic variability of the sea medium and for acoustic tomography of the dynamic processes in a shallow sea. In the experiment, combined acoustic transmitting and receiving systems (transceivers) and complex phase-manipulated signals with a carrier frequency of 2500 Hz were used. The velocities of currents calculated from the acoustic data agree satisfactorily with the velocities measured by standard methods of oceanography.