The threat of asymmetric attacks against ships and harbours has led to the development and launch of a new diver detection sonar by QinetiQ.
The attack on the USS Cole in Yemen, which claimed the lives of 17 American sailors and caused severe damage to the destroyer in October 2000, alerted governments to threats posed by small explosives-laden speedboats, as well as from divers or small underwater vehicles.
QinetiQ’s sonar unit, named Cerberus, was unveiled at UDT (Undersea Defence Technology) 2003 and reportedly provides diver detection at a range of around 700 metres.
Cerberus can be deployed as a single unit to provide 360-degree cover for ship protection by being slung from the side of the vessel. Alternatively, a number of units can be attached to the seabed in a cordon to provide harbour security and channel protection. Deployed in this manner, the detection range is extended to one kilometre and beyond.
The main technical challenge in safeguarding ships and harbours from such threats has been the difficulty in locating a human diver because of the lack of a strong sonar target return. Extremely limited underwater visibility greatly reduces the effect of underwater surveillance techniques relying on cameras operating in the visible band.
The units carry sonar arrays and signal processing electronics that are linked by cable to a shore station. The systems provide alerts, location confirmation and multiple target tracking and are tuned to deal with the complex environmental conditions that may arise in individual harbours. Cerberus utilises high definition sonar imaging techniques together with a high-resolution 100kHz-wideband active search sonar. This can be complimented with a 300kHz active imaging sonar and a 2-8kHz passive capability, which allows threat detection at sufficient range to allow an effective counter-threat response.
According to QinetiQ, swimmers have been successfully detected at ranges of 700 metres by a single Cerberus unit during open, shallow water trials. This range can be extended to one kilometre and beyond with carefully placement of a cordon of units. Target classification is also provided, enabling operators to decide on an appropriate response.
The sonar return provided by the target when using Cerberus is said to be detailed enough to allow the identification of the distinctive human chest cavity at distances approaching 500 metres. The operator can therefore distinguish between the potential terrorist human diver and similar sized sea mammals.