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This paper discusses the results of an experimental study of the spatial structure of a scalar-vector sound field formed during towing of a low-frequency acoustic source on the continental shelf of the Sea of Japan. Methodologically, the experiment was carried out by towing the acoustic source emitting a 134 Hz tone signal at a depth of 20 m on various acoustic paths at distances of up to 10 km from the combined receiving system, which consisted of a sound pressure receiver and three orthogonal sound pressure gradient components. Particular attention was paid to the investigation of the interference structure of scalar and vector fields in controlled hydrological conditions. The quantitative characteristics and features of the formation of signal interference at several depths along the tracks are discussed. The most interesting are the unique results of comparing horizontal and vertical field components, which make it possible to identify the presence of vortex structures in the acoustic source field on several tracks. The possibility of practical application of current research results is analyzed.

Nowadays, more and more complex methods of signal modulating and processing are actively used for organizing underwater acoustic communication with and between submerged mobile vehicles due to harsh underwater conditions. In this research, the method that is based on multi-frequency signals forming (OFDM) with the constant envelope is applied to the problem. It is based on multi-frequency FM-OFDM signals forming with Quadrature Phase Shift Keying (QPSK) modulated subcarriers and FM spectrum spreading coefficients of 1, 2, 4, and 10. The proposed solution was modeled in a software simulator, which implements a noisy underwater acoustic multipath channel, changing the bit error rate (BER) from 0.15 to 10 −3 . In addition, it was tested during the full-scale data transmission experiments at 25 km distance using a low frequency (400 Hz) underwater acoustic apparatus under conditions of strong impulse noises and quasi-non-stationary channel. The results of in-situ experiments were similar to the ones that were obtained during the simulation.