The ChemSight: an open-path, multichemical detector for security applications
2011
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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