The flying detectors

The US military is to use helicopter-mounted metal detection systems to sweep Iraq in its search for concealed weapons of mass destruction.

The newly-developed device from the Oak Ridge National Laboratory in Tennessee, uses three separate technologies to identify the location and type of objects buried up to 11m below ground.

3D maps can be generated within 24 hours, helping to locate unexploded mines and certain types of cluster bombs that can then be diffused by engineers, said David Bell, ORNL’s director of advanced environmental technology and assessment.

‘We are in discussion with the US Army Corps of Engineers for deploying this in Iraq and are talking about the logistics of getting it over there and manning it in what is still a dangerous area. This will be the primary system for screening areas to detect the extent of contamination. We will be able to detect caches of weapons as well as drums containing documents or even chemical agents.’

The technology is capable of scanning areas of between 400 and 800 acres a day using a 12m-long structure fixed to the base of a helicopter, protruding from both sides and to the front, and allowing the system to scan a 12m-wide area.

The structure’s three scanning technologies operate as the plane flies at between 46 to 69 mph and around 3m above the ground. This produces images as clear as those gathered by bomb disposal experts when manually inspecting areas on the ground, but in a fraction of the time.

Ferrous metals such as stainless steel, or iron used as casings for weapons or oil drums, are identified using magnetic signals from eight caesium vapour magnetometers spaced at even intervals along the array. These are capable of detecting even slight changes in the Earth’s magnetic field.

Another electromagnetic imaging system consisting of a transmitter coil around the edge of the array transmits electronic signals into the ground, which are then bounced back and picked up by sensors.

Differences between the signal sent out and that received allow identification of non-ferrous metals such as brass and aluminium, distinguishing between bombs and waste. This second system will be useful in areas where the magnetometer may confuse minerals in the ground with hidden weapons.

Last, the array contains pairs of highly-sensitive magnetometers deployed in pods at the far edges of the boom, away from interference caused by rotor noise.

Their position allows them to measure vertical magnetic gradient, producing a 3D image. The pods create a clearer picture at greater heights and help to distribute weight to maintain helicopter flight stability.