Acoustic tomography for monitoring the Sea of Japan: a pilot experiment

A pilot experiment was conducted in the Sea of Japan (also called the East Sea) in September-October 1999, to assess the possibility of using acoustic tomographic techniques for monitoring water mass structure and dynamics. Acoustic m-sequence signals at various frequencies between 250 and 634 Hz were transmitted from bottom-mounted acoustic sources in shallow water off the coast of Vladivostok to vertical-array receiving systems deployed off the north coast of Ulleung-Do island (S. Korea), 558 km to the south. The data are analyzed for temporal correlation, time spread, and transmission loss and are interpreted in terms of a tomographic system for monitoring the East Sea.     

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.

     

Application of complex acoustic signals in communication systems and navigation of submersible units

Doklady Earth Sciences -     

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.     

Features of the Formation of the Pulse Characteristics of Waveguides by the Long-Range Propagation of Acoustic Signals in Underwater Sound Channels

Doklady Earth Sciences - 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...