Passive localization of moving targets based on the energy leakage from ocean surface duct

Target localization using passive azimuth-only measurements obtained by a circular array is difficult. Specifically, when the target and the array travel at constant velocities, there are multiple possible trajectories of the targets. In this condition, the target is unobservable. This paper presents a method to solve this problem in the ocean environment with surface duct. When the sound frequency is below the cut-off frequency, the sound energy in the duct or outside the duct quickly attenuates with the horizontal range at a constant rate. Therefore, the energy difference between two observations of the array implies the horizontal range difference of the target relative to the array. By utilizing this extra measurement, the moving target becomes observable.