Offshore barges fitted with a long-range radar system originally designed for oceanography could be used to protect ships and ports from seaborne terrorists.
Following boat attacks on the French tanker Limburg in October and the USS Cole in 2000, business and the military are nervous about so-called ‘asymmetric’ threats to shipping.
The system, developed by US defence and electronics company Raytheon, has concluded trials to demonstrate its functions against small boats. Design work has also been completed for the 100m barges that could carry the radar to survey ‘threat areas’ such as Yemen. For long-term power needs the barges would be fitted with solar cells.
Known as the High-Frequency Surface Wave Radar (HFSWR), the sensor is adapted from technology normally used to monitor ocean currents. Most GHz (or millimetre-wave) radars can only find objects in their ‘line of sight’, meaning they can’t ‘see’ beyond the curvature of the earth. So low-flying aircraft or small boats may move undetected under the radar. Range is also limited to about 150km, though a typical coastal radar might only be effective up to 25km.
However, HF radar falls between 3 and 30MHz. Conducted by the water surface, the radar waves can follow the contours of the earth. This means that HF can work over the horizon out to about 400km, but only recently have engineers been able to tune it for surveillance applications.
Raytheon business development manager Jim Bunnell explained that in the past 90 days an HFSWR system based on prototypes built in Canada was demonstrated to the US Navy. The trials involved 10m boats, skidoos and jet-skis, he said, but the system may also be able to detect ballistic missiles or light aircraft.
The beauty of the system, said Bunnell, was that it could see all these simultaneously, as tests in the Bahamas during September illustrated. It could also compare its readings against a database of boat cross-sections to help spot unwelcome vessels. For search-and-rescue applications, he added, radar tracks from the past 24 hours could be quickly played back on a computer to help coastguards find the last known position of a stricken vessel.