3 June 2011 The ChemSight: an open-path, multichemical detector for security applications
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The performance of an open-path, multi-chemical detector designed for continuous, long line-of-sight monitoring is described. The detector system is comprised of an infrared source that projects a collimated broad-spectrum beam towards a detector, which can be located up to 45 m away from the source. The detector spectrally analyzes the beam with an array of room-temperature pyroelectric detectors integrated with bandpass filters. When chemicals intercept the beam, they are detected and identified by a non-linear Mahalnobis distance based detection and identification algorithm, which matches each newly recorded IR absorption spectrum against chemical signatures stored in the detector's onboard, remotely updatable database. Using this algorithm, multiple chemicals can be detected and identified under high humidity conditions and in the presence of interfering chemicals. The sensor and algorithm were tested in the laboratory and field deployments, including continuous operation trials at public transportation centers, office buildings, and chemical storage facilities. In laboratory tests, the detector was presented with various chemicals at known optical densities in a gas containment cell. Different environmental conditions were simulated by varying the relative humidity of the air in the cell and introducing interferent gases. The laboratory tests were used to establish minimum detection sensitivities under varying conditions. Field test data were used to evaluate false negative and false positive rates, and field operation characteristics. These tests demonstrated below IDLH concentration sensitivity for the chemicals tested, no false positive identifications, and no false negatives to field test challenges.
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S. Keith Holland, S. Keith Holland, Gabriel Laufer, Gabriel Laufer, } "The ChemSight: an open-path, multichemical detector for security applications", Proc. SPIE 8018, Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XII, 80181R (3 June 2011); doi: 10.1117/12.883861; https://doi.org/10.1117/12.883861


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