<title>LWIR multispectral imaging chemical sensor</title>

Abstract

Physical Sciences Inc. (PSI) has developed an Adaptive IR Imaging Spectroradiometer, comprised of a low-order tunable Fabry-Perot etalon coupled to an HgCdTe detector array, for passive, stand-off detection of chemical vapor plumes. The tunable etalon allows coverage of the 9.5 to 14 micrometers spectral region with a resolution of approximately 7 cm^-1 and provides the capability to obtain monochromatic images of a scene at only those wavelengths needed for chemical species identification and quantification. The adaptive sampling capability of the etalon allows suppression of background clutter and minimization of data volume. The tuning time between transmission wavelengths is typically approximately 10 ms, however the mirror tuning system may be operated to obtain tuning times as short as 1.3 ms. We present results using a brassboard imaging system for stand-off detection and visualization of chemical vapor plumes against near ambient temperature backgrounds. This data shows detections limits of 22 ppmv m and 0.6 ppmv m for DMMP and SF₆ respectively against a (Delta) T of 6 K. The reported detection limits are consistent with the measured system noise-equivalent spectral radiance, approximately 2 (mu) W cm^-2 sr^-1 micrometers ^-1.