Equivalent Width
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Equivalent Width
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In spectrography, a measure of the total absorption
of radiant energy as indicated by an absorption
line or absorption
band. Compare line width.
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The formula for equivalent width W is
A is the fraction of incident radiation which is absorbed at any wavelength,
and Missing Image:img src="SP7-e_files/lambdasm.gif"1 and Missing Image:img src="SP7-e_files/lambdasm.gif"2 are wavelengths, on opposite sides of
the line or band, where the absorption has dropped to zero.
Thus, in a
plot of A against Missing Image:img src="SP7-e_files/lambdasm.gif", the equivalent width
represents the area under the curve, or the width of a fictitious line or band
which absorbs completely throughout its extent but which absorbs the same
total amount of energy as the actual line or band.
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References
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use
