V. V. Bezotvetnykh

Experimental studies of pulsed signal propagation from the shelf to deep sea

Results of an experimental study of low-frequency broadband pulsed signal propagation in a waveguide that includes the shelf zone, the continental slope, and the deep sea region are presented. Using phase-manipulated signals with central frequencies of 366 and 600 Hz, pulsed characteristics are measured at six points along the propagation track, the maximal distance from the source being 368 km. It is experimentally demonstrated that, in the presence of a negative sound velocity gradient in the near bottom layer on the shelf with a small bottom slope, the choice of the source position at the shelf bottom near the shoreline provides the formation of a continuous illumination zone in the deep sea near the USC axis and a stable pulsed characteristic with two main sound energy arrivals. The propagation velocity of the pulse that is last to arrive is identical (within the measurement error) to the velocity of sound on the USC axis at the point of reception. Possibilities for practical application of the results obtained from the experiment are discussed.

Acoustic tomography of dynamic processes in a sea shelf zone with the use of complex signals

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.

Specificities of applying pseudorandom sound signals to measuring impulse responses on the shelf of the Sea of Japan

Solving the problems of underwater acoustic communication and navigation for controlling underwater objects greatly depends on a correct estimation of the hydrological and acoustical environment in the region. Analysis of the domestic and foreign experience in the field of navigational support of self-contained underwater devises shows that, to solve the problem, it is technically and economically advantageous to deploy a set of fixed sources of navigation signals in the region with a range of coverage that is at least not less than the size of the region of interest. At long distances and, especially, in a shallow-water sea, the key factors in solving the problem of navigation are correct determination of the efficient sound speed and the time of signal propagation for each path connecting sources and receivers.

A mobile measuring complex for studies in the field of acoustic navigation of remote submersibles

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.

Processing of acoustic signals and computer modeling instrumental and programming measuring complex for acoustic navigation investigations

This paper describes the main systems and results of testing a mobile instrumental programming complex developed for experiments on investigation of the influence of hydrophysical processes in the marine environment on the quality of solving the navigation problems using stationary acoustic beacons.

Acoustic remote sensing of currents at the shelf of the Sea of Japan

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.

Acoustohydrophysical Complex for Marine Tomographic Research

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.

A hardware and software system for measuring the angular structure of the acoustic fields in acoustic tomography

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.

An Acoustic Transceiver for Monitoring Dynamic Processes in the Ocean

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.

A telemetric measurement complex for acoustic and hydrophysical investigations

A hardware-software complex that allows synchronous measurements of hydroacoustic noises and signals, the temperature, and the pressure at a specified point and provides transmission of theses characteristics via a radio channel and their recording in a shore-based analytical center is described. The offshore part of the complex includes a GPS receiver for testing the location during drift. The results of an experimental approbation of the complex during acoustic thermometry of a water area in the Vityaz bay of the Posiet gulf in the Sea of Japan are presented.