Study of Arrival Times of Pulse Signals in the Case of Shallow-to-Deep Propagation in Waveguides of the Sea of Japan

The paper presents a description of the results of a full-scale experiment conducted in August 2023 in the Sea of Japan on the transmission and reception of pulsed acoustic signals for the “shallow-to deep” scenario. A feature of the experimental waveguide is its division into shallow and deep-water parts, approximately equal in length. The results of mathematical modeling of the propagation of pulsed acoustic signals from the shelf zone to the deep sea for this track are discussed. The modal structure of the field in the waveguide is described, theoretical estimates of the arrival times of the modal components of the acoustic signal are obtained. The formation of a dense group of modal components of small numbers, which is not typical for this class of problems, is discovered and theoretically explained. This phenomenon is associated with both the configuration of the waveguide, divided in approximately equal parts into deep-water and shallow-water parts, and with the orientation of the acoustic path at an acute angle relative to the depth gradient, which creates conditions for the occurrence of the phenomenon of horizontal refraction. A comparison of the experimental impulse responses of the waveguide and the estimates of the arrival times gives reason to believe that a distinctive feature of acoustic paths of this type is the formation of two maxima of the impulse response function.