Effects of Sound Velocity Perturbations in the Upper Layer on the Position of Sound Convergence Zones in Deep Water

Sound velocity profiles (SVPs) data of deep water is measured by an underwater glider in South China Sea. The measured data show that the SVP in the upper layer has a small perturbation at the experiment site. The maximum fluctuation of Sound velocity occurs at 110 m and the standard deviation of the fluctuation is 2.8 m/s. The standard deviation of fluctuations is 1.5 m/s at 200 m, which is the source depth of acoustic experiment. And the measured data of a temperature chain at a fixed place shows that there are no strong internal waves during the experiment. The numerical simulations show that the fluctuations of upper layer SVPs during the experiment have a great effect on the convergence zone (CZ) span of acoustic field in the deep water. This results in that CZ position of deep-water acoustic field has a certain deviation and this deviation value increases with propagation distance. The propagation paths of the sound ray with a grazing angle of 0° is calculated under different SVPs fluctuation, and we analyze the reasons for the influence of SVP perturbations on CZs position of acoustic field in deep water. The average SVP is used to calculate acoustic propagation loss at experiment site. The simulated acoustic propagation loss and measured results are consistent with each other, which indicate that using average SVP can effectively reduce influence of the upper layer sound velocity perturbations on predicting CZs position of acoustic field in deep water.