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Proceedings Paper

Differences in concentration lengths computed using band-averaged mass extinction coefficients and band-averaged transmittance
Author(s): W. Michael Farmer
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Paper Abstract

An understanding of how broad-band transmittance is affected by the atmosphere is crucial to accurately predicting how broad-band sensors such as FLIRs will perform. This is particularly true for sensors required to function in an environment where countermeasures such as smokes/obscurants have been used to limit sensor performance. A common method of estimating the attenuation capabilities of smokes/obscurants released in the atmosphere to defeat broad-band sensors is to use a band averaged extinction coefficient with concentration length values in the Beer-Bouguer transmission law. This approach ignores the effects of source spectra, sensor response, and normal atmospheric attenuation, and can lead to results for band averages of the relative transmittance that are significantly different from those obtained using the source spectra, sensor response, and normal atmospheric transmission. In this paper we discuss the differences that occur in predicting relative transmittance as a function of concentration length using band-averaged mass extinction coefficients or computing the band-averaged transmittance as a function of source spectra. Two examples are provided to illustrate the differences in results. The first example is applicable to 8- to l4-um band transmission through natural fogs. The second example considers 3- to 5-um transmission through phosphorus smoke produced at 17% and 90% relative humidity. The results show major differences in the prediction of concentration length values by the two methods when the relative transmittance falls below about 20%.

Paper Details

Date Published: 1 September 1990
PDF: 12 pages
Proc. SPIE 1312, Propagation Engineering: Third in a Series, (1 September 1990); doi: 10.1117/12.21884
Show Author Affiliations
W. Michael Farmer, Bionetics Corp. (United States)

Published in SPIE Proceedings Vol. 1312:
Propagation Engineering: Third in a Series
Luc R. Bissonnette; Walter B. Miller, Editor(s)

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