Stevens Passive Acoustic System for underwater surveillance

Abstract

The Stevens Passive Acoustic System allows the detection, tracking and classification of various surface and underwater sources of sound including surface vessels, swimmers, various types of divers, and unmanned underwater vehicles. This system was developed by Stevens in its Maritime Security Laboratory, which was established to support research in the area of Anti-Terrorism and Force Protection. The focus of this lab has been the persistent detection and classification of threats posed by surface and subsurface intruders utilizing a multiplicity of technologies. Using these capabilities, we have investigated the set of acoustic parameters fundamental to underwater acoustic threat detection, including diver acoustic signatures, acoustic transmission loss, and acoustic environmental noise. The Stevens Passive Acoustic System has successfully demonstrated surface ship detection and classification. The system provides simultaneous acquisition and analysis of acoustical signals using 4 hydrophones. The analysis functions includes arbitrary digital filtering, spectral analysis and cross-correlation for simultaneous processing of signals from several hydrophones, acoustical source separation, and determination of bearing for different targets relative to the central underwater mooring. The system also records and stores the complete raw acoustical data set, enabling further research and analysis of the acoustic signals. Novel acoustic methods of signal processing used in the system include: 1. Method of precise hydrophone localization. 2. Cross-correlation method for target bearing determination 3. Cross-correlation methods for extraction of target signatures from numerous sources. 4. Feature-based automated diver detection algorithm. 5. Measurements of the ship noise modulation spectrum that is related to propeller and shaft rotation (Detection of Envelope Modulation on Noise - DEMON method). The Stevens Passive Acoustic System has been used in tests in the Hudson River and NY Harbor where a large library of ship acoustic signatures has been collected. Several US Navy sponsored trials demonstrated the ability of the Stevens system for effective diver detection at distances up to 700m.