There is a worldwide need for improved methods for the
screening of air cargo for contraband. The main objectives
are the detection of contraband such as illicit drugs,
explosives, weapons and nuclear materials and the
verification of declared manifests.
Air cargo is usually packaged into lightweight aluminium
containers called unit load devices (ULDs). The most
common ULDs have a width of about 1.6 m and gross
weight of up to 1.6 tonnes. However, pallet ULDs are
significantly larger, with widths up to 2.4 m and maximum
gross weights of up to 6.8 tonnes. For comparison, the
most common sea container is the 40 ft container of
dimensions 12.2 m (length) 2.4 m (width) 2.6 m (height)
and maximum gross weight of 32.5 tonnes. The air cargo
ULD content is commonly limited by its mass, not its