Passive Acoustic Array Harbor Security Applications

Abstract

Harbor security and protection of maritime assets are issues of increasing concern. Outstanding research questions exist in terms of the optimal protection methodology needed for the wide variety of surface and submerged threats and diverse geographical locations. Economic costs and environmental concerns are also significant overriding issues. Acoustic methods have the advantage of being amenable to tracking and detecting targets both above and below the ocean surface. Moreover, passive acoustic methods are nonintrusive and capable of covering extensive ranges. Acoustic arrays offer significant advantages in terms of gain and signal processing capabilities over discrete, single hydrophones. We investigate the use of horizontal and vertical arrays for the detection and tracking of a remote environment monitoring system (REMUS) autonomous underwater vehicle as well as open-circuit divers in a noisy, shallow water environment. Using conventional beamforming techniques, we obtain positive preliminary results for detection and tracking, which highlight the overall merits of an acoustic array implementation.

A two-hydrophone range and bearing localization algorithm with performance analysis

“…Passive acoustic signals were collected in August 2011 by a moored horizontal line array (HLA) at the Kilo Nalu Nearshore Reef Observatory (Gebbie et al, 2011). The observatory provided power and ethernet connectivity via an undersea cable running approximately 0.4 km from shore to a fixed underwater station deployed in roughly 12 m of water.…”

Demonstration of passive acoustic detection and tracking of unmanned underwater vehicles

“…Since the cold war, passive sonar tracking has been the main technique for submarines to track surrounding targets but remain stealth. Passive sonar is also advantageous for not disrupting marine life, avoiding multipath propagation and interference, and driving down costs [49]. Passive sonar tracking has also been integrated onto UUVs for the purpose of ASW.…”

“…However, with new capabilities come new threats. In terms of national security, UUVs are now useful tools for tracking submarines [57], invading harbors [49], and collecting oceanographic data in restricted areas [13]. They are desirable for their covertness, ability to navigate shallow waters, and multiplication of force.…”

Partial dereverberation used to characterize open circuit scuba diver signatures

“…Several active acoustic systems are available for port security applications (Shaw et al, 2005;Folegot et al, 2008;Suchman and Meurling, 2010), which have the ability to detect low signal-to-noise ratio (SNR) sources, such as divers. In favorable multipath environments, SCUBA divers were detected at about 500 m (Suchman and Meurling, 2010) and intercepted at 350 m. However, the use of active systems can be limited in reverberant, nearshore environments (Gebbie et al, 2011). An active system may falsely classify sources with similar scattering characteristics, it requires an operator and has a higher up front cost than a passive system.…”

“…Detection distances for the port of Gothenburg (Sweden) were on the order of 30 m for a single hydrophone. Nearshore reef environments (Kilo Nalu, Island of Oahu, Hawai'i) were analyzed (Gebbie et al, 2011) using two 24element L-shaped hydrophone arrays, with resulting detection ranges of about 20-30 m. Integrated passive detection systems to detect underwater sources have been investigated, as have systems to deter swimmers (Sutin and Sinelnikov, 2010).…”