Extinction Coefficient

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Extinction Coefficient

In meteorology, a measure of the space rate of diminution, or extinction, of any transmitted light; thus, it is the attenuation coefficient applied to visible radiation. The extinction coefficient Missing Image:img src="SP7-e_files/epsilonsm.gif" is identified as

dI = -Missing Image:img src="SP7-e_files/epsilonsm.gif"I dx
I = I0 e-Missing Image:img src="SP7-e_files/epsilonsm.gif"x
where I is the

illuminance (luminous flux density) at the selected point in space, I0 is the illuminance at the light source; and x is the distance from the source. </dd>
When so used, the extinction coefficient equals the sum of the medium's absorption coefficient and scattering coefficient, each computed as a weighted average over all wavelengths in the visible spectrum. As long as scattering effects are primary, as in the lower atmosphere, the value of the extinction coefficient is a function of the particle size of atmospheric suspensoids. It varies in order of magnitude from 10 per kilometer with very low visibility to 0.01 per kilometer in very clear air. </dd>


This article is based on NASA's Dictionary of Technical Terms for Aerospace Use