Topics in Particle and Dispersion Science

Attenuation coefficient

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Attenuation coefficient of light in a medium, customarily denoted by c [length^-1], is defined by the following equation:

dΦ(z) = -cΦ(z) dz

(1)

where Φ [power] is the power of light flowing only in the positive direction of the z-axis, z [length] is the distance. This equation leads to the Lambert law of attenuation of light in a medium. Note that the attenuation coefficient may depend on position in the scattering medium. In the medical optics literature, the attenuation coefficient is frequently denoted by symbol µ_t.

The inverse of the attenuation coefficient is referred to as the attenuation length. It is the average distance between photon attenuation events (scattering and/or absorption):

zc = 1 / c

(2)

The attenuation coefficient represents the combined losses due to light absorption and scattering of light power propagating in a turbid medium. Hence, it is a sum of the absorption coefficient, a, and the scattering coefficient, b:

c = a + b

(3)

In the oceanographic literature, the attenuation coefficient is also referred to as the beam attenuation coefficient (for example, Voss KJ 1992). The attenuation coefficient is sometimes referred to as the extinction coefficient. The latter name is also used in referring to the imaginary part of the refractive index and to the molar absorption coefficient (Braslavsky SE 2007, p. 338). The use of the qualifier "extinction" should probably be discouraged because extinction of light implies the complete removal of light power rather than its gradual reduction (see also Braslavsky SE 2007, p. 338).

See also single scattering albedo.

CITATION: Jonasz M. 2006. Attenuation coefficient (www.tpdsci.com/Tpc/AtnCf.php). In: Top. Part. Disp. Sci. (www.tpdsci.com).

HISTORY: Published: 17-Jan-2006 Modified: 16-Nov-2009 Peer-reviewed: 19-Feb-2007

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