The results of an experiment conducted in September 2017 are considered with regard to the applicability of the acoustic "mudslide" effect for positioning autonomous underwater vehicles (AUV) operating substantially deeper than the axis of the deep sound channel (DSC). The results of the experimental study and numerical analysis of the effect of focusing acoustic energy in the bottom layer on the Sea of Japan shelf and transitional zone with the deep water (up to 500 m deep) for summer-autumn hydrological conditions are presented. Mathematical modeling of the propagation of acoustic waves in a waveguide reproducing the experimental conditions using the parabolic equation method has been performed. The effective propagation velocities of the signal are explained in terms of the modal-analysis method.

The results of an experiment conducted in September 2017 to substantiate the applicability of the “acoustic mudslide” effect when solving the positioning problems of autonomous underwater vehicles in cases of their operation at depths substantially exceeding the depth of the axis of the underwater sound channel are discussed. The results of the experimental studies and numerical analysis of the effect of an acoustic energy focusing in the near-bottom layer of the shelf and its transition into deep-water (up to 500 m) layers of the Sea of Japan for summer-autumn hydrological conditions are presented. Mathematical modelling of the propagation of acoustic waves in a model waveguide reproducing the experimental conditions using the parabolic equation method has been performed. The observed effective signal propagation speeds are explained using the normal wave method.

The article discusses the application of methods and means of general and satellite oceanology for the high-precision acoustic positioning of autonomous underwater vehicles (AUVs) at distances of hundreds of kilometers from control stations. The authors present the results of analyzing their long-term acoustic ranging studies, which revealed the specific features of low-frequency pulsed signal propagation in different hydrological–acoustic conditions in which underwater sound channels (USCs) of different origin form. Special attention is devoted to the possibility and efficiency of using long-term oceanological observation databases to form the spatiotemporal characteristics of USCs in areas for long-range navigation support to AUVs. Additionally, the authors consider the possibilities of sea surface observation by means of satellites to provide the unit that computes the AUV coordinates with data on the integral (effective) sound speed in the near-surface sound channel (NSSC), which forms in winter. The experimental testing results on applying oceanographic technical tools in the Sea of Japan have shown that they improve the accuracy and reliability of AUV navigation support at distances of hundreds of kilometers from coastal control stations. It is been shown that in summer–autumn and winter hydrological conditions, it is possible to determine the AUV coordinates with errors not exceeding hundredths of a percent at distances of hundreds of kilometers.

Solving tasks of underwater acoustic communication and navigation for controlling underwater objects much depends on right hydrology and acoustic media condition estimation in operation area. Technically and economically it is worth to deploy on a operation area a stationary source of navigational and communication signals system with the range of functioning equal to operation area maximum size. For navigational system tasks each source in direct period of time beam a unique signal, which is recognized by underwater object and then propagation time and distance is been calculated. In this examination the using of a complex phase manipulated signals with carrier frequency 2000 Hz and 6000 Hz as sounding signals is been tested. These signals were used for transmitting information and navigational data. Beside their beam let to measure and examine waveguide impulse characteristics on the acoustic tracks. In current work the experiment results of informational signal transfer in case of shelf sea is shown.

Results of experimental researches of virtual hydroacoustic system of the time reversal mirror (TRM) are presented. In this virtual TRM processing in spatial area is replaced by temporary processing. Application of complex phase-manipulated signals (M-sequences) in this virtual TRM allows, as well as in a classical case, successfully to suppress the multiplicate noises caused by an interference of signals. These signals (multipath) have various random amplitudes, delays and phases, and also various Doppler's displacement due to probable movements of the source, the receiver or environment. Experiments were on stationary paths in Sea of Japan. Technical support of experiments included acoustic sources in a range of 250-3500 Hz, single hydrophones, two-element interferometers and vector-phase receivers. In experiments and at the subsequent data processing it is shown, that our virtual hydroacoustic system of TRM is efficient and can be useful for navigation of sea objects, underwater communication, monitoring of dynamic processes at ocean, ets.

In this work results of experiments with virtual hydroacoustic system of the time reversal mirror (TRM) are presented. In this virtual TRM processing in spatial area is replaced by temporary processing the complex phase-manipulated signals (M-sequences) with addition modulation by short sequences with good correlation properties. Experiments were spent in 2005-2006 on stationary path at Sea of Japan. The method of TRM finds application for the decision of a lot of applied problems of hydroacoustics. It is focusing of a field, active nulling, communication, etc. For the characteristic of scale of works in this direction, it is possible to specify that fact, that for the researches connected with various aspects of a method, are actively used specialized ranges of the Center of underwater researches of NATO (Spezia, Italy) and Marine physical laboratory (San Diego, the USA), and results of researches have found reflection in V.A. Kuperman's numerous publications, etc. (1-7). In this connection it is necessary to note works in M. Finn (8-11) and V.A.Zverev (12-14). In particular, considered in (14) opportunity, under some conditions to replace processing in spatial area with processing in time, it is put in a basis of the present work. The classical principle of the TRM assumes transmitting of a signal s(t) a probe source; receiving of a signal ri(t), the past through waveguide with the pulse characteristic hi(t), i-th element of the vertical receiving-transmitting array and retransmitting the signals turned by time in a point of an arrangement of a probe source where the passive vertical array registers a signal () s t % . The sequence of stages of the classical TRM is represented by means of the operator of convolution * as follows: () st ; () ( ) * ( ) ii rt s t h t = ; () i rt − ; 1 i st s t s t h t h t ' ' = −− % . Assuming hi(t)=h ' (t)=h(t), that is a constancy of conditions of propagation of signals si(t) and s ' (t), we shall estimate influence of the factor q(t)=h(-t)*h(t), and it is describing the basic idea of a TRM-method actually. We shall present the accepted signal in the form:

In this paper, the lines of investigation on a problem of the development of remote acoustic sensing methods in oceanology are formulated. This paper summarizes the results of investigations into the possibilities for monitoring temperature and flow fields in shallow seas. In the discussed experiments, the instrumentation being constituents of the complex for longduration remote monitoring of marine medium climatic variability and that of the acoustic tomography of shallow sea dynamic processes is used. The acoustic instruments were located on the POI FEB RAS acousto-hydrophy sical polygon (Pacific Oceanological Institute, Far Eastern Branch of the Russian Academy o f Sciences) near the Gamov Peninsula. Acoustic receiving and transmitting systems operating with multiplex phase-manipulated signals (of M-codes) at frequency range 250-2500 Hz form the basis for this complex.

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.

In the shallow waters any acoustic field is the super-position of running and standing waves. The report under consideration offered some results of stringent solution of Helmholz's equation taking into account actual parameters of bottom ground, marine water and surface. This algorithm admits to calculate dispersion of pressure, oscillation velocity and stream of energy in every point of a closed space including the space near surface. The results of mathematical exploration of array's field that arose from 20 elements in closed volume, distribution of the group velocity, energy transfer inside marine bay are displayed. These results of digital research are compared with the experimental testing performed at the Peter the Great Bay (Japan Sea).

The possibility of kinematic parameters acquisition from acoustic field using vector-phase measurements of marine water was considered. The developed method includes measurement reception and localization of complex phase-manipulated signals in time. Such kinematic parameters as the phase and group velocities are calculated by way of reciprocal processing of acoustic pressure ranges and oscillation velocity (or pressure gradient) in the vector receiver. Concept of acoustic field presents the availability to apply notion "invariant velocity" as a kinematic parameter that possesses considerably lower spatial-temporal variability. Stringent solution of Helmholtz's equation for the pressure, oscillation velocity and energy stream, as Green's function, indicated that theoretical explorations were satisfactorily confirmed by the experimental data.

Experimental data are presented on the use of single receiving and transmitting systems in acoustic tomography of dynamic processes in a shallow sea. The experiments are based on the use of the transmission tomography and opposite-direction sounding with complex phase-manipulated signals. The original data are those obtained by the authors in 1990–2000 on the shelf of the Sea of Japan near the Gamov Peninsula, in the vicinity of the acoustical-hydrophysical experimental site of the Pacific Oceanological Institute. A possibility of using combined transmitting-receiving systems (transceivers) for monitoring the temperature and fields of currents in the ocean is demonstrated.

An acoustic transceiver for the monitoring of dynamic processes in the ocean by acoustic tomography methods is described, and the results of its tests are presented. At an acoustic pressure of 2–6 kPa/m produced by the transceiver in the emission mode at frequencies of ∼250 Hz and an rms error in determining time intervals no larger than 2 ms, the flow velocity component can be measured to an accuracy of 10 cm/s by using the countersounding scheme.

An acoustohydrophysical complex for tomographic ocean surveillance is described. The complex has been developed within the framework of the US–Russia project JESAEX (The Japan / East Sea Acoustics Experiment). Technical characteristics of self-contained and mobile receiving and transmitting systems of the complex allow one to use them as building blocks in constructing tomographic systems of various configurations and complexities. Experimental tests of methods and facilities in September–October 1999 in the Japanese sea have shown that the range of reliable reception of composite phase–shift keyed signals, such as M—sequences, is 700 km at an acoustic pressure produced by a sound source of up to 7 000 Pa/m.

Summary form only given. Self-contained transmitting and receiving acoustical systems were developed for acoustical monitoring of the oceanic shelf environment. The 250-Hz electromagnetic transducers with 50-Hz bandwidth, the 12-element line vertical array provided with the acoustic positioning unit and measurement unit of the vertical distribution of temperature, the 12-element of two dimensions horizontal array, the United World Time (UWT) unit and the unit of data transmission through radio-communication channel were included as the components of these systems. These systems have been tested and were applied to carry out acoustic experiments in the shelf area of the Sea of Japan. The group travel time of acoustic field modes were measured through transmitting, receiving and cross-correlative processing of a 225-symbol m-sequence code signals. Such measurements, when sounding in one direction and in the other make it possible to determine the projection of current velocity and sound speed perturbation on the acoustic travel.