Passive Underwater Event and Object Detection Based on Time Difference of Arrival

Underwater event/object detection is an enabling technique for many marine applications. for the surveillance of target water areas, the future underwater network can serve as a backbone system, and every sensor in this network is an agent. When the target moves into the target area or when an event happens, the agents will detect acoustic signals from the target or event. The acoustic waves arrive at different agents at different time. Based on the correlation of the received signals between two agents, the time difference of arrival (TDoA) can be estimated, which locks the target/event's position on one branch of a hyperbola, represented by a nonlinear equation. With three or more agents, the target/event's position can be uniquely decided. To make this system universally applicable, the average underwater acoustic velocity is also assumed to be unavailable, and a two-phase linear algorithm is proposed. A coarse estimation is obtained in Phase I, and the result is further refined in the Phase II. Extensive simulations are provided to verify the effectiveness of the proposed system.