A. A. Golov

A study of how temperature field variations affect accuracy in measuring the distance to underwater objects

The paper presents the experimental testing results for an acoustic method that increases the accuracy of measuring underwater object positioning systems; the method is based on application of temperature field measurement data in a water area where an underwater object functions. Measurements conducted in September 2011 in Vityaz Bay of Possiet Bay have shown that application of the method permits a two- to threefold reduction in the positioning error related to the change in the sound propagation conditions.

Acoustic-hydrophysical testing of a shallow site in coastal waters of the Korean Strait

The paper describes the results of testing experiments for solving problems of thermometry and positioning of an autonomous underwater vehicle (AUV) in the Korean Strait in a shallow sea with less than 10 m of water. The studies were conducted on acoustic tracks up to 615 m long, sensed with complex phase-shift keyed signals with a centeral frequency of 2500 Hz. Under field experiment conditions, it was shown that the resolution of the structure of pulse responses makes it possible to sense temperature changes less than one degree and to secure positioning of the AUV with an accuracy better than 1 m when operating in the near-bottom layer.

Peculiarities of the Formation of the Interference Structure of Scalar-Vector Acoustic Fields on the Shelf of the Sea of Japan

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.

Experimental Testing of High-Accuracy Underwater Range-Finding Technology

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.

Propagation of pulse pseudorandom signals from a shelf into shallow water in winter hydrological conditions of the Sea of Japan

The paper discusses the results of an experiment conducted in the Sea of Japan in March 2016 on an acoustic track 194 km long under winter hydrological conditions. We have studied the most complex case of propagation of pulse pseudorandom signals from the shelf into shallow water during vortex generation on the acoustic track. Analysis of the experimentally obtained pulse characteristics have shown that the maximum first approach of acoustic energy recorded at all points agrees well with the calculation. This testifies to the fact that at a given reception depth, the first to arrive are pulses that have passed in the near-surface sound channel over the shortest distance and at small angles close to zero. We propose a technique for calculating the mean sound velocity on the track from satellite monitoring data on the surface temperature, which makes it possible to rely on the successful application of the results obtained in acoustic ranging and navigation problems.

Real-time remote current velocity and direction estimation by means of hydroacoustic reciprocal sound transmission method

This paper presents results from experimental testing of the hardware-software system that was developed to realize real-time remote current velocity and direction estimation by means of a hydroacoustic reciprocal sound transmission method in a very shallow water area with significant tide level (around 4 meters) of Norek island (Korea Republic). The data obtained in the experiment for the current velocity show good correlation with the tide level variation.

Experimental studies of the possibility of remote measuring of the velocity and direction of currents in the shallow water area of the Korean strait

893 Studying the dynamic processes in shallow water areas and the possibility of measuring the hydrophysi cal parameters of the water environment are important in the development of the coastal shelf, which is a pri ority goal for economics and various applied spheres. In 2010, the Institute of Science and Technology (city of Gwangju, Republic of Korea) and Ilyichev Pacific Oceanological Institute, Far East Branch, Russian Academy of Sciences, established the Center for Marine and Information Technologies as the base for complex studies aimed at designing and testing techni cal means under in situ conditions for developing and studying the shallow–water areas in the Sea of Japan. The Center is located on Norek Island in the southern part of the Korean Peninsula. The shelf zone of the island features shallow depths of the adjacent water areas (down to 10 m) and high (up to 3 m) tidal amplitudes. In 2010 the experiments on acoustic ther mometry showed the possibility to monitor the tem perature variations in this area with an accuracy up to tenths of a degree [1]. It was also recorded that the time resolution for the structure of the pulse responses makes it possible to measure successfully the velocities of sea currents in the future using the method of counter sensing [2, 3]. This area requires estimating the variations in a field of currents, since it is actively used for fishing. In November 2013, there was an experiment to evaluate the possibility of measuring the velocity and direction of the current in this water area by the method of counter sensing. The purpose of the experiment was to measure the current velocity by the difference between the times of signal propagation in the direct and opposite directions along a path that was chosen arbitrarily, using two zero overlapped sources and receivers of acoustic signals (transceivers). In this case, it was meant that a positive result of measure ments along this path could be used for solving the full scale problem of measuring a field of currents (the amplitudes of velocities and directions as functions of coordinates) in the water area by placing additional transceivers.

Experimental testing of a hardware and software complex for remote measurement of current velocities and temperatures in shallow sea water areas

We describe a technique and hardware-software implementation for remote monitoring of sea currents and temperature using data from pulsed hydroacoustic sounding on stationary horizontal tracks in shallow sea water areas. As sounding signals, we used complex phase-manipulated signals based on pseudorandom M-sequences. The complex was tested in Posiet Bay in the Korea Strait in the Sea of Japan.

Examination of the complex signals distribution conditions influence

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.

Acoustic-hydrophysical experiments in the coastal zone of the Korean Peninsula

This paper presents the results of a pilot experiment on determination of the possibility for effective application of the navigational systems of autonomous robots and remote tools of water structure and dynamics monitoring in shallow water areas. The experiment was based on investigation of the regularities of formation and interaction between hydroacoustic and hydrophysical fields when sounded by complex phase-shift keyed signals with the central frequency of 2500 Hz. The possibility of monitoring of temperature and current fields by acoustic tomography methods in the water area of several square kilometers in size and no more than 10 m in depth, at depth changes up to several meters due to tidal effects, was studied. Additionally, the possibility and precision of solution of navigational problems for underwater objects at such shallow depths was studied. For this purpose a hardware-software complex, equipped with two sources of navigational signals and an imitator of the submersible receiver path, was used.