SMALL BOAT LOCALIZATION USING TIME DIFFERENCE OF MULTIPATH ARRIVALS FROM TWO BOTTOM MOUNTED HYDROPHONES

摘要

Modern day harbors face a multitude of security threats ranging from smuggling of illicit materials to terrorism. In this regard, small surface vessels are of particular concern due to their speed and agility. A key capability of any harbor security implementation is the ability to track the movement of small surface vessels. While shore-based systems use RADAR, infrared sensing, or optical techniques, passive acoustic methods are attractive due to their minimal impact on the environment, inconspicuousness, and robustness to weather. A passive acoustic system consisting of two or more hydrophones placed within a few meters of each other on the seabed will record the noise emitted by passing small boats. Since small boats typically have wideband noise signature characteristics, cross-correlating the recorded signals will yield an estimate of the time-difference of arrival (TDOA) allowing the target's bearing to be estimated. Emitted noise is often loud enough that the bottom-surface image is also detectable. This paper investigates the use of the TDOA between the bottom-surface image and the direct path to additionally estimate the range to the target. Projection of the cross-correlation time-series onto the ocean surface facilitates visualization of target location ambiguity. Use of bathymetric data also increases the accuracy of localization and breaks the left-right ambiguity typically associated with line arrays. Experimental data collected using a hydrophone array deployed in shallow water near Honolulu Harbor, Hawai'i, USA, is compared with GPS data of a small boat, which provides ground truth for the target position.