Algorithms for Rapid and Accurate Depth Localization of Targets for Mine Avoidance

This work proposes to develop an efficient algorithm for rapid and accurate depth localization of mine-like targets in shallow water environments where both direct and multi-path wave propagation exists. The proposed algorithm is an extension of an existing table look-up approach for direct path refraction correction, which has been implemented in real time software at the Atlantic Undersea Test and Evaluation Center (AUTEC) for improved depth localization of targets on range. In this approach, the major computational effort associated with the time-consuming, trial-and-error ray tracing to determine the actual refracted path for each eigen ray (either direct or multi-path) between the emitted pulse from the ship's sonar and the target's reflected position, is conducted prior to implementing the real-time localization based on sound velocity and travel time. The result of this a priori computation is termed the effective sound velocity between two positions for the specific ocean environment (SVP and bathymetry) and is stored in tables in terms of various depths and depression/elevation angles. During the real-time localization process, only simple interpolations are required to obtain the effective sound velocity (which is significantly different from the true sound velocity at various depth locations) between the ship and target positions.