Chapter 7 - Longwave infrared spectral reflectance techniques for measuring explosives

Abstract

Longwave infrared (LWIR) reflectance spectroscopy probes fundamental molecular vibrations of explosive materials and therefore provides a spectral fingerprint that can be used for identification. Measurements are made from standoff (10s of m) to proximal (~1m) distances using active illumination (quantum cascade, supercontinuum lasers, or thermal sources) and sensitive LWIR detectors. Spectral resolution is obtained by spectrally tuning the illumination source in time or by employing a spectrally selective detector such as an interferometer or imaging spectrometer. Automated identification is performed by advanced algorithms tailored to isolate the explosive materials’ spectral signatures in the presence of scene clutter. The following chapter provides a survey of LWIR spectral sensor architectures that have been reported for the detection of explosive material on surfaces. Physical models of spectral signatures of explosive materials in thin film, bulk and particulate form are presented.