Prediction of broad band attenuation computed using band-averaged mass extinction coefficients and band-averaged transmittance

W. Michael Farmer

doi:10.1117/12.55948

1 September 1991 Prediction of broad band attenuation computed using band-averaged mass extinction coefficients and band-averaged transmittance

W. Michael Farmer

Author Affiliations +

Optical Engineering, Vol. 30, Issue 9, (September 1991). https://doi.org/10.1117/12.55948

Abstract

A common method of estimating the attenuation capabilities of military smokes/obscurants is to use a band-averaged mass 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 on broadband transmittance characteristics, which can significantly affect broadband transmittance. The differences that can occur in predicting relative transmittance as a function of concentration length by using band-averaged mass extinction coefficients as opposed to more properly computing the bandaveraged transmittance are discussed in this paper. Two examples are provided to illustrate the differences in results. The first example considers 3- to 5-μm and 8- to 14-μm band transmission through natural fogs. The second example considers 3- to 5-μm and 8-to 12-μm transmission through phosphorus-derived smoke (a common military obscurant) produced at 17% and at 90% relative humidity. Major differences are found in the values of concentration lengths predicted by the two methods when the transmittance relative to an unobscured atmosphere falls below about 20%. These results can affect conclusions concerning the detection of targets in smoke screens, smoke concentration lengths required to obscure a target, and radiative transport through polluted atmospheres.

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W. Michael Farmer "Prediction of broad band attenuation computed using band-averaged mass extinction coefficients and band-averaged transmittance," Optical Engineering 30(9), (1 September 1991). https://doi.org/10.1117/12.55948

Published: 1 September 1991

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