# Hemispherical attenuation coefficient

## Description

Attenuation coefficient or narrow beam attenuation coefficient of the volume of a material characterizes how easily it can be penetrated by a beam of light, sound, particles, or other energy or matter. A large attenuation coefficient means that the beam is quickly “attenuated” (weakened) as it passes through the medium, and a small attenuation coefficient means that the medium is relatively transparent to the beam. The SI unit of attenuation coefficient is the reciprocal metre (m−1). Extinction coefficient is an old term for this quantity, but still used in meteorology and climatology.

Hemispherical attenuation coefficient of a volume, denoted μ, is defined as shown here.

Related formulas## Variables

μ | hemispherical attenuation coefficient (m^{-1}) |

Φ_{e} | radiant flux (watt) |

dΦ_{e} | radiant flux rate (watt) |

dz | path length of the beam (m) |