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.
Stevens Institute of Technology has established a research laboratory environment in support of the U.S. Navy in the
area of Anti-Terrorism and Force Protection. Called the Maritime Security Laboratory, or MSL, it provides the
capabilities of experimental research to enable development of novel methods of threat detection in the realistic
environment of the Hudson River Estuary. In MSL, this is done through a multi-modal interdisciplinary approach. In
this paper, underwater acoustic measurements and video surveillance are combined. Stevens' researchers have developed
a specialized prototype video system to identify, video-capture, and map surface ships in a sector of the estuary. The
combination of acoustic noise with video data for different kinds of ships in Hudson River enabled estimation of sound
attenuation in a wide frequency band. Also, it enabled the collection of a noise library of various ships that can be used
for ship classification by passive acoustic methods. Acoustics and video can be used to determine a ship's position. This
knowledge can be used for ship noise suppression in hydrophone arrays in underwater threat detection. Preliminary
experimental results of position determination are presented in the paper.
KEYWORDS: Acoustics, Video, Sensors, Signal attenuation, Data modeling, Homeland security, Visualization, Data centers, Interference (communication), Global Positioning System
Stevens Institute of Technology has established a new Maritime Security Laboratory (MSL) to facilitate advances in
methods and technologies relevant to maritime security. MSL is designed to enable system-level experiments and data-driven
modeling in the complex environment of an urban tidal estuary. The initial focus of the laboratory is on the
threats posed by divers and small craft with hostile intent. The laboratory is, however, evolvable to future threats as yet
unidentified. Initially, the laboratory utilizes acoustic, environmental, and video sensors deployed in and around the
Hudson River estuary. Experimental data associated with boats and SCUBA divers are collected on a computer
deployed on board a boat specifically designed and equipped for these experiments and are remotely transferred to a
Visualization Center on campus. Early experiments utilizing this laboratory have gathered data to characterize the
relevant parameters of the estuary, acoustic signals produced by divers, and water and air traffic. Hydrophones were
deployed to collect data to enable the development of passive acoustic methodologies for maximizing SCUBA diver
detection distance. Initial results involving characteristics of the estuary, acoustic signatures of divers, ambient acoustic
noise in an urban estuary, and transmission loss of acoustic signals in a wide frequency band are presented. These
results can also be used for the characterization of abnormal traffic and improvement of underwater communication in a
shallow water estuary.
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