Multi-platform sonar-based systems for submerged threats operating in littorals

A key clement in maritime security is the protection of littorals against underwater threats. Protecting the littorals requires a surveillance system to detect under water platforms attempting to penetrate into the protected harbor. Surveillance systems comprised of fixed detection systems have been previously proposed. The large number of platforms and sensors required to search the entire coastal region of most countries makes fixed systems cost-prohibitive. A highly mobile surveillance system containing an affordable number of platforms and sensors that can quickly deploy to an area offers a viable alternative. The surveillance system concepts analyzed in this paper fall into the category of responsive mobile sonar systems. More specifically, the platforms considered include helicopters and high-speed surface craft, either manned or unmanned. Sensors include dipping sonar and lightweight variable depth sonars (VDS). The threat platforms are quiet underwater vehicles, either modern diesel-electric submarines or small high-capability mini-subs. The acoustic environments considered are littorals that contain shallow water and sloping bottoms extending to deep water. The objectives of the surveillance system are (1) to search a semicircular area having a radius of 200 nautical miles centered at the entrance to a harbor and (2) to establish a barrier at the entrance to the harbor. The performance predictions presented in the paper show that systems synthesized from currently available technologies are effective. Measures of effectiveness include the number of platforms required to search the area in a time less than the time required for the threat to transit the area. Multi-platform systems of one to four helicopters and four to eight, manned high-speed surface craft (RHIB) meet surveillance system requirements. Since the multi-platform systems are based on available technologies, the estimated time required to integrate these technologies to create the systems considered in the paper is less than six months.