ABSTRACT
Prior to the tragic events of September 2001, aviation detection technology incorporated walk-through metal detection systems, cabinet X-ray systems, and limited use of computed tomography (CT) and trace explosive detectors (Connelly et al. 1998). Metal detectors can be set for various thresholds of alarm, but were generally set to interdict concealed ‡rearms. Cabinet X-rays image the contents of containers and can dižerentiate between organic and inorganic substances, but, depending on the power and energy pro‡le of the X-ray, cannot penetrate high-atomic-weight substances, such as lead. Cabinet X-rays are also dependent on operation by a trained security o²cer who can discern an improvised explosive device (IED) in a ‡eld of clutter in the container. In the late 1990s, there was limited piloting of automated explosive detection systems (EDSs; ‡rst-generation CT X-ray systems) for detection of explosive masses concealed in checked luggage as well as explosive trace detection systems (ETDs; mainly based on detection via ion mobility spectrometry, or IMS). EDSs have the advantage of automatically detecting explosives by matching average density and the average atomic number of a threat to a library of explosives without manual intervention. Alarms can be resolved by a visual examination of the potential threat article by the screener. If additional veri‡cation is warranted, the article can be further analyzed by performing an analysis for trace residues with an ETD. Trace explosive detection devices work by collecting residues ož of surfaces and performing a chemical analysis.
