An Analysis of Atmospheric Aerosol Scattering for Mid-Infrared Systems

Report No. ARL-TR-3938
Authors: Richard C. Shirkey; Sean G. O?Brien
Date/Pages: September 2006; 48 pages
Abstract: Electro-optical sensors that operate in the mid-infrared region of the electromagnetic spectrum (from 3?5 ?m) in the planetary boundary layer can detect atmospheric radiance from a number of source mechanisms, including scattering of direct solar radiation, thermal emission radiance, and secondary scattered thermal radiance from all aerosols and gases. While scattered radiation is of little consequence in the farinfrared region, in the mid-infrared it can reduce a sensor?s ability to detect targets by reducing their contrast. In order to determine under what atmospheric conditions scattering in the mid-infrared is significant, we present an analysis of the scattering and emission of some typical aerosols under varying atmospheric conditions. To further delineate whether or not scattering is significant, we present contrast calculations, define a ?scattering fraction,? and present examples of hypothetical sensor curves for determination of optimal spectral placement in the midinfrared. In general, we find that for most aerosols and atmospheric conditions, scattering in the mid-infrared cannot be ignored and greatly reduces the contrast available for target detection.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2006