The Maritime Security 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 conducted a set of tests in the Hudson River near Manhattan in order to
measure 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 diver's sound with
a reference signal from a calibrated emitter placed on his path. Transmission loss was measured by comparing noise
levels of passing ships at various points along their routes, where their distance from the hydrophone was calculated with
the help of cameras and custom software. The ambient noise in the Hudson River was recorded under varying
environmental conditions and amounts of water traffic. The passive sonar equation was then applied to estimate the
range of detection. Estimations were done for a subset of the recorded noise levels, and we demonstrated how variations
in the noise level, attenuation, and the diver's source level influence the effective range of detection. Finally, we
provided analytic estimates of how an array improves upon the detection distance calculated by a single hydrophone.
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