Two-stage diver tracking in a high-clutter harbor environment.

Abstract

One approach to detecting swimmers with active sonar is to deploy a larger number of relatively simple nodes and network them together. Instead of using a complex multi-element phased array with electronic beamforming, this system uses air-backed parabolic reflectors, each with an omni-directional transducer. To avoid performance degrading acoustic interactions, the available operating frequency band is managed at the channel level. The physical configuration of this sonar system presents challenges for tracking through and across beams, and between nodes. Swimmers can exhibit low target strength and the acoustic clutter fields can be dense and highly dynamic. To detect and track swimmers in this environment, we employ a windowed Hough-transform (HT) tracker at the beam level. The HT has received wide use for track initiation. However, because of the processing gain required to continually track a weak target in such a significant clutter field, the HT is used in this case to maintain as well as to initiate tracks. The single- and multi-node tracker is a Kalman-based, multi-object tracker capable of tracking any number of stationary, constant-velocity and/or maneuvering targets. The multi-node tracker receives fused observations as inputs and creates accurate estimates based on the target position, velocity, and acceleration.