Imaging alone does not give a complete identification of explosives. It is clearly a major advantage to combine an image with a measurement of the specific explosive composition. Many composition detection techniques only identify an anomalous nitrogen content, and do not provide conclusive evidence of the presence of an explosive device. A combined image, showing wires or a dielectric shape in the form of an explosive device and an anomalously large nitrogen concentration, would enhance the decision-making task. An example of a portal scenario with combined imaging and nitrogen concentration is a backscatter X-ray image of a truck along with a neutron scattering signal showing anomalously high nitrogen concentrations. Another example is a suicide bomber imaged by a terahertz scan paired with an indication of explosive molecules by a LIDAR signal from the plume of vapors arising from the bomber.
Recommendation: Research is needed on new spectroscopic and imaging methods employable at a distance (passive and active). Examples include terahertz and microwave imaging and spectroscopy and X-ray backscattering.