Attenuation coefficient

attenuation coefficient

(Also called extinction coefficient, especially in reference to optical frequencies.) For radiation propagating through a medium, the fractional depletion of radiance per unit pathlength, or in radar usage, of the power density of plane-wave radiation per unit pathlength.

The attenuation coefficient is defined through Bouguer's law as

where L is the monochromatic radiance at a given wavelength, γ is the attenuation coefficient, and ds is a differential increment of pathlength. So defined, the attenuation coefficient is the same as the volume extinction coefficient and has dimensions of inverse length. In radar, the usual convention is to measure the depletion of power on a decibel scale in terms of the specific attenuation Y, which is related to attenuation coefficient by

where Y is in decibels per kilometer when γ is in inverse kilometers. The numerical factor in this equation is 10 log₁₀e.

A radiometric term for the rate at which radiant energy in a set of directions confined to a unit solid angle around a particular direction is transferred across unit area of a surface (real or imaginary) projected onto this direction.

(Coined word for radio detection and ranging.) An electronic instrument used for the detection and ranging of distant objects of such composition that they scatter or reflect radio energy.

1. Regular markings on an instrument used to allow the reading of the measured quantity or setting.