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

The study presents the results of a field experiment conducted in August 2023 in the Sea of Japan on the transmission and reception of pulsed acoustic signals in a “shallow-to-deep” scenario. The experimental track consists of the shallow-water and the deep-sea parts of nearly equal length. The results of mathematical modeling of pulsed signal propagation along the track are discussed, the modal structure of the field in the waveguide is described, and theoretical estimates of the arrival times of the modal components of the acoustic signal are obtained. The formation of two separated in time beams of low-order mode components is observed and explained. This phenomenon is related both to the configuration of the waveguide divided into approximately equal shallow and deep parts, and to the acoustic track orientation at an acute angle to the depth gradient, which creates conditions for the occurrence of horizontal refraction. The comparison of the impulse response functions obtained during the experiment and the theoretical arrival-time estimates indicates that a distinctive feature of acoustic tracks of this type is the splitting of the main peak of the waveguide pulse response, and the appearance of two separate maxima.