A Target Localization Method Based on Surface Duct Leakage Signals

Due to factors such as wind, waves, and temperature, a waveguide layer with a positive sound speed gradient forms near the sea surface, known as the surface duct. When sound waves approach the bottom of the surface duct at an incidence angle close to 0°, some energy leaks downward due to boundary effects, a phenomenon referred to as surface duct leakage (SDL). The signals generated from the leaked energy are called SDL signals, and the propagation paths of these signals is known as the SDL paths. The propagation process of surface duct signals can be explained by the Segmented Propagation Model (SPM). SDL signals exhibit multipath characteristics, and their multipath delay differences can be used to estimate the depth of sound sources in the shadow zone. Furthermore, the propagation time of SDL signals is sensitive to horizontal distance, demonstrating excellent performance in distance estimation. Based on these, this paper proposes a method for localizing shadow zone targets based on the arrival structure of SDL signals. By simultaneously calculating the propagation time and multipath delay differences of SDL signals using SPM, two-dimensional spatial searches can be conducted to locate sound sources in the shadow zone. Simulation results validate the feasibility of the method.