Waveguide-Invariant-Based Target Motion Estimation Using Dual Hydrophones in Shallow Water

This paper presents a passive dual-hydrophone method for estimating target motion parameters, including the closest point of approach range and source speed. The proposed approach exploits broadband time-frequency striation patterns that embed target motion information, whose structure is governed by the waveguide-invariant parameter beta. Time-frequency striation information extracted from two horizontally separated hydrophones is incorporated into a joint nonlinear least-squares framework. This framework reduces the unbounded ambiguity inherent in single-hydrophone striation-based estimation to a finite set of geometrically ambiguous solutions. We further show that four geometrically distinct solutions persist within this reduced solution set and present an in-depth analysis of the associated residual ambiguity. The proposed method is validated using both numerical simulations and experimental data obtained from a surface ship radiating broadband noise in approximately 100m deep shallow water, recorded by two bottom-moored hydrophones with a separation of 5.6km.