Estimation of passive acoustic threat detection distances in estuarine environments

Abstract

The Maritime Secure Laboratory (MSL) at Stevens Institute of Technology supports research in a range of areas relevant to harbor security, including passive acoustic detection of underwater threats. The difficulties in using passive detection in an urban estuarine environment include intensive and highly irregular ambient noise and the complexity of sound propagation in shallow water. MSL measured the main parameters defining the detection distance of a threat: source level of a scuba diver, transmission loss of acoustic signals, and ambient noise. The source level of the diver was measured by comparing the divers sound with a reference signal from a calibrated emitter placed on his path. Transmission loss was measured using the transmission of a sweep signal (1–100 kHz) from the calibrated emitter. The passive sonar equation was then applied to estimate the range of detection. Estimations were done for various recorded noise levels, demonstrating how fluctuations in noise level and the mobility of the diver influence the effective range of detection. Finally, analytic estimates of how a hydrophone array improves upon the detection distance calculated by a single hydrophone are shown. [This work was supported by ONR project No. N00014-05-1-0632: Navy Force Protection Technology Assessment Project.]