Detection of Explosives by Hyper-Spectral Differential Reflectometry
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Detection of Explosives by Hyper-Spectral Differential Reflectometry Thierry Dubroca1 and Rolf E. Hummel1 1
Department of Material Science and Engineering, University of Florida, Rhines Hall, Gainesville, Florida 32611-6400 ABSTRACT In the wake of the recent terrorist attacks, such as the 2008 Mumbai hotel explosion or the December 25th 2009 “underwear bomber”, our group has developed a technique (US patent #7368292) to apply differential reflective spectroscopy to the problem of detecting explosives in order to detect terrorist threats. Briefly, light (200-500 nm) is shone on a surface such as a piece of luggage at an airport or a parcel at a courier distribution center. Upon reflection, the light is collected with a spectrometer combined with a camera. A computer processes the data and produces in turn a differential reflection spectrum taken between two adjacent areas of the surface. This differential technique is highly sensitive and provides spectroscopic data of explosives. As an example, 2,4,6, trinitrotoluene (TNT) displays strong and distinct features in differential reflectograms near 420 nm. Similar, but distinctly different features are observed for other explosives such as RDX, PETN or ANFO. Our detection system uses a two dimension detector (CCD camera) which provide spatial and spectroscopic information in each of the two dimensions. By scanning (involving fixed optical equipment and scanning moving bags or parcels on a conveyor belt), the surface to be surveyed the system provide the spatial location of the potential threat. We present in this paper how our detector works and how it is applied to the problem of explosive screening for explosives at airports and mail sorting centers. Additionally, we will present the effect of the explosives morphology on the detection response. In particular we will evaluate the implication on the limit of detection of the instrument as well as discuss the sample morphology with respect to a realistic threat scenario. INTRODUCTION Differential reflectometry is a powerful optical technique, which is capable of detecting small amounts (that is, traces) of explosive materials[1-6]. This standoff technique can be used at airport baggage checking areas, mass transit facilities, and parcel screening centers at commercial shipping companies. One of our thrust areas is to investigate which parameters have an influence on the differential reflectograms of explosives, such as the electron configurations of the molecules, environmental influences, reproducibility, contamination of the substances, possible influences of taggants, differentiation between explosives and harmless substances, distinction between different types of explosives, possible common features of various explosives, sensitivity of the technique, possible variations of mixtures of different explosives, and influences of substrates (plastics, metals, canvas etc.). Moreover, one of our goals is to understand the mechanisms which cause the differential reflectograms of explosives by applying molecular model calc
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