<!-- Deleted image removed: thumb|240px|Diagram of Beer-Lambert Law of transmittance of a beam of light as it travels through a [[cuvette of width l.]] -->

thumb|Earth's atmospheric transmittance over 1 nautical mile sea level path (infrared region). Because of the natural radiation of the hot atmosphere, the intensity of radiation is different from the transmitted part.

thumb|240px|Transmittance of ruby in optical and near-IR spectra. Note the two broad blue and green absorption bands and one narrow absorption band on the wavelength of 694 nm, which is the wavelength of the [[ruby laser.]]

Electromagnetic radiation can be affected in several ways by the medium in which it propagates.  It can be scattered, absorbed, and reflected and refracted at discontinuities in the medium.  This page is an overview of the last 3. The transmittance of a material and any surfaces is its effectiveness in transmitting radiant energy; the fraction of the initial (incident) radiation which propagates to a location of interest (often an observation location). This may be described by the transmission coefficient.

Surface transmittance

Hemispherical transmittance

Hemispherical transmittance of a surface, denoted T, is defined as

:<math>T = \frac{\Phi_\mathrm{e}^\mathrm{t{\Phi_\mathrm{e}^\mathrm{i,</math>

where

  • Φ<sub>e</sub><sup>t</sup> is the radiant flux transmitted by that surface into the hemisphere on the opposite side from the incident radiation;
  • Φ<sub>e</sub><sup>i</sup> is the radiant flux received by that surface.

Hemispheric transmittance may be calculated as an integral over the directional transmittance described below.

Spectral hemispherical transmittance

Spectral hemispherical transmittance in frequency and spectral hemispherical transmittance in wavelength of a surface, denoted T<sub>ν</sub> and T<sub>λ</sub> respectively, are defined as

:<math>\tau = \sum_{i = 1}^N \sigma_i n_i\ell,</math>

:<math>A = \sum_{i = 1}^N \varepsilon_i c_i\ell.</math>

Cases of non-uniform attenuation occur in atmospheric science applications and radiation shielding theory for instance.

Other radiometric coefficients

See also

  • Opacity (optics)
  • Photometry (optics)
  • Radiometry

References