Peculiarities in the formation of the sound field structure of a point source in the Black Sea underwater sound channel

This paper studies unique (characteristic only of the Black Sea) peculiarities of the underwater sound channel (USC). Changes in the sound velocity of at depths of 50–250 m, forming the lower boundary of the Black Sea USC, differ fundamentally from the corresponding areas of the profile c(z) in other regions of the world ocean. With lowering from 40–50 m (by 5–10 m lower than the level of the channel axis) to 200–250 m, the sound velocity gradient decreases monotonically from 0.08–0.22 to 0.02 1/s (and does not increase like in the majority of regions of the world ocean). The end portion of an explosion signal received in the Black Sea USC at a distance of 200 km or more from the source represents a quasi-harmonic signal with a gradually changing frequency. Moreover, the end portion of the signal has an explicitly block structure, which agrees well with the block structure of the spectrum of an explosion signal element. In the truncated τ(R) diagram, there is no sharp bend characteristic of the majority of regions of the world ocean. At comparatively small depths of the Black Sea, a sufficiently rapid increase in the complete duration of a multiray signal with distance is observed. A comparative analysis is conducted of experimental materials obtained with a difference of seven years on virtually the same long-range propagation path of explosion signals. The main reasons for the interannual variability in the conditions of sound channel propagation in the Black Sea are explained.