Sound convergence zones formed by reflection from the sea bottom in an incomplete sound channel

The seafloor has a significant influence on sound propagation in deep water in the context of an incomplete sound channel. Using data collected during an experiment in the South China Sea, we study seafloor reflection effects on sound propagation in a range dependent environment. The experiment phenomenon is different from the convergence phenomenon in the deep sound channel, also referred to as the SOFAR channel. We observe that the spatial variation of bathymetry contributes to the formation of the seafloor reflection convergence zone in advance, and the sound intensity in some areas of the shadow zone is significantly increased. Due to seafloor reflection, there are two seafloor reflection convergence zone within 60 km of the propagation track, in which the gains of the acoustic energy can exceed 10 dB. High sound intensity areas are also observed in the shadow zone near 11 km and 51 km at some depths. In addition, the gain of the second convergence zone is higher than that of the first convergence zone when the receiving depth is the same as the source depth. In the first convergence zone, as the receiving depth increases, the arrival structure tends to become complicated, and the multipath effect becomes more obvious. Numerical analysis based on the parabolic equation and ray theory is carried out to explain the physical mechanism of the seafloor reflection convergence zone. The study result is meaningful for the performance analysis of sonar in complex deep-water environments.*