At-Sea Evaluation of an Underwater Vehicle Behavior for Passive Target Tracking

In this paper, we describe an unmanned underwater vehicle (UUV) behavior designed to track nearby vessels using bearing-only measurements obtained from a rigidly mounted planar hydrophone array—one that was originally designed for active sonar use but is repurposed for passive sonar use. Upon detecting a target, a maneuver is executed to resolve the port/starboard bearing ambiguity. The maneuver is heuristically designed with the aim of reducing the effects of end-fire, self-noise during maneuvers, and other noise/spurious measurements on the bearing ambiguity decision. After resolving the bearing ambiguity, the vehicle continuously adjusts its heading to track the target by keeping it broadside to the array. The performance of this behavior, as well as that of the passive sonar itself, is evaluated through field trials in the approaches to Boston Harbor using a Bluefin-21 UUV. In total, 19 successful behavior tests are described where the UUV resolves the bearing ambiguity and tracks either a static source emitting a predefined waveform or the platform noise of a medium-sized catamaran underway.