Studies of Spatiotemporal Structure of the Acoustic Field Formed in Deep Water by a Broadband Pulsed Signal Source on the Shelf of the Sea of Japan

The article discusses the results of experiments conducted in September 2017 to prove the applicability of positioning underwater objects during their operation at depths substantially exceeding the depth of the underwater sound channel axis. The authors present results of experimental studies and numerical analysis of the effect of focusing of the acoustic energy in the near-bottom layer on the shelf and its transition into deep-water (up to 500 m) layers of the Sea of Japan for summer-autumn hydrological conditions. Experiments on reception of broadband pulsed signals with a center frequency of 400 Hz were carried out at various distances (20, 68, 86, 90, and 198 km) from a source of navigation signals moored at a depth of 35 m at the shoreline near Cape Schulz. The receiving of acoustic signals was performed by a system of distributed over depth up to 500 meters hydrophones, with the possibility of long-term signal recording at fixed depths and during submergence. The experimental results allowed to study the impulse responses of acoustic waveguides, and estimate the effective propagation velocities of navigation signals received at different depths, and to draw conclusions about the possibility of solving positioning problems for autonomous underwater vehicles at depths up to 500 m and distances up to 200 km from the source of navigation signals. Mathematical modeling of acoustic wave propagation in a waveguide reproducing the experimental conditions by the normal mode technique was also carried out.