Prediction of the limits of detection of hazardous vapors by passive infrared with the use of modtran.
Passive infrared remote detection of hazardous gases, vapors, and aerosols is based on the difference, Δ T, between the air temperature of the threat vapor cloud and the effective radiative temperature of the background. In this paper I address the problem of detection with a low-angle-sky background. I used Modtran to predict Δ T and atmospheric transmittance for standard atmospheric models. The detection limits, at 2-cm(-1) resolution, are discussed for sulfur hexafluoride, Sarin, trichloroethylene, methyl isocyanate, mustard gas, methyl chloride, and sulfur dioxide for selected cases with the U.S. Standard, the Subarctic Winter, and the Tropical models. I used a particularly interesting case of Sarin detection with the Subarctic Winter atmospheric model to illustrate the power of Modtran to predict subtle changes in Δ T with angle of elevation (AOE).
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Flanigan