# Extinction coefficients

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## extinction coefficient

(

*Also called*attenuation coefficient, especially in reference to radar frequencies.) For radiation propagating through a medium, the fractional depletion of radiance per unit path length.The volume extinction coefficient is defined through Beer's law as where

*L*is the monochromatic radiance at a given wavelength, γ is the volume extinction coefficient, and*ds*is an increment of path length. The mass extinction coefficient equals the volume extinction coefficient divided by the density of the medium. Thus, in SI units, the volume extinction coefficient has units of inverse meters and the mass extinction coefficient has units of square meters per kilogram. In general, extinction of radiant energy is caused by absorption and scattering. The extinction coefficient is the sum of the absorption coefficient and the scattering coefficient, and generally depends on wavelength and temperature.*Compare*specific attenuation.