Abstract

Imaging spectrometry enables passive, stand-off detection and analysis of the chemical composition of gas plumes and surfaces over wide geographic areas. We describe the use of a long-wavelength infrared imaging spectroradiometer, comprised of a low-order tunable Fabry–Perot etalon coupled to a HgCdTe detector array, to perform multispectral detection of chemical vapor plumes. The tunable Fabry–Perot etalon used in this research provides coverage of the 9.5–14-µm spectral region with a resolution of 7–9 cm-1. The etalon-based imaging system provides the opportunity to image a scene at only those wavelengths needed for chemical species identification and quantification and thereby minimize the data volume necessary for selective species detection. We present initial results using a brassboard imaging system for stand-off detection and quantification of chemical vapor plumes against near-ambient-temperature backgrounds. These data show detection limits of 22 parts per million by volume times meter (ppmv × m) and 0.6 ppmv × m for dimethyl methyphosphonate and SF6, respectively, for a gas/background ΔT of 6 K. The system noise-equivalent spectral radiance is approximately 2 µW cm-2 sr-1 µm-1. Model calculations are presented comparing the measured sensitivity of the sensor to the anticipated signal levels for two chemical release scenarios.

© 1999 Optical Society of America

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