A review of standoff detection technologies for explosives has been made. The review is focused on trace detection methods (methods aiming to detect traces from handling explosives or the vapours surrounding an explosive charge due to the vapour pressure of the explosive) rather than bulk detection methods (methods aiming to detect the bulk explosive charge). The requirements for standoff detection technologies are discussed. The technologies discussed are mostly laser-based trace detection technologies, such as laser-induced-breakdown spectroscopy, Raman spectroscopy, laser-induced-fluorescence spectroscopy and IR spectroscopy but the bulk detection technologies millimetre wave imaging and terahertz spectroscopy are also discussed as a complement to the laser-based methods. The review includes novel techniques, not yet tested in realistic environments, more mature technologies which have been tested outdoors in realistic environments as well as the most mature millimetre wave imaging technique.

Standoff identification of explosives at distances of up to 55 m has been performed by applying spontaneous Raman spectroscopy. This work has been focused on detection in a realistic environment, using an outdoors test field and performing experiments under varying weather conditions such as rain‐ or snowfall or bright sunshine. The instrumentation, based on a 532 nm pulsed laser source combined with gated detection, proved the performance insensitive to weather variations. Investigated HMEs and precursors were TATP, HMTD, HP, MEKP, NM, NB, and IPN; all in bulk quantities. The time needed for acquiring spectra was typically between single pulse (5 ns) and 10 s. Detection through green and brown glass bottles and PET bottles were tried and found viable.

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