On the Advantage of Wideband Data Acquisition for Passive Diver Detection

Situation awareness is an important component of security that justifies the equipment of sites with monitoring systems. For shore/harbour security, these systems are mostly composed of camera and radar, to monitor the land and the water surface, and of active sonar(s) when the underwater situation is monitored.
An alternate approach for underwater monitoring is to use a network of passive sonars that detect targets by the sound they radiate. Unlike active sonar, a single passive sonar element cannot estimate the range of a target in the far field, only its direction; but it can characterize the sound radiated by a target, with obvious applications to target tracking and classification. Passive sonars, with frequency characteristics suitable for the target type of interest, have to be deployed as a network so that the source location can be estimated by appropriately crossing the estimated directions.
TNO and the Stevens Institute of Technology are investigating this approach for diver detection and have conducted in 2010 a trial with the support of the Royal Netherlands Navy. A system involved in the trial presented a wide sampling dynamic and frequency range, making it suitable not only for diver detection but also for other forms of processing. Experimental results demonstrate that the deployed system can be used for diver detection and that its larger-than-required dynamic range enables other applications such as boat tracking and sound speed estimation, that can not only augment but improve the initial diver detection capability.