An improved positioning model of deep-seafloor datum point at large incidence angle

The inhomogeneous sound speed in seawater causes refraction of sound waves, and the elimination of the refraction effect is essential to the accuracy of underwater acoustic positioning. The ray-tracing method is an indispensable tool for effectively handling problems. However, this method has a conflict between localization accuracy and computational quantity. The equivalent sound speed profile (ESSP) method uses a simple sound speed profile (SSP) instead of the actual complex SSP, which can improve positioning precision but with residual error. The residual error is especially non-negligible in deep water and at large beam incidence angles. By analyzing the residual error of the ESSP method through a simulation, an empirical formula of error is presented. The data collected in the sailing circle mode (large incidence angle) of the South China Sea are used for verification. The experiments show that compared to the ESSP method, the improved algorithm has higher positioning precision and is more efficient than the ray-tracing method.