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An **Equation Of Radiative Transfer** (or
**Radiative Transfer Equation** or **RTE** or **Transfer Equation**)
is an equation that describes Radiative Transfer, the transfer
of energy by EMR through a gas or Plasma, taking into account factors
that can remove Photons (Absorption) and can
insert them (Emission). One form:

1 ∂ ^ — ——I+ Ω˙∇_{ν}I+ (_{ν}k+_{ν,s}k)_{ν,a}I=_{ν}j+ 1/(4π)_{ν}k∫_{ν,s}Ic ∂_{ν}dΩt

- c - speed of light
- t - time
*I*- Intensity_{ν}*ν*- Frequency*k*- Absorption Coefficient*k*- scattering Opacity_{ν,s}*k*- absorption opacity_{ν,a}*j*- Emission Coefficient_{ν}- Ω - Solid Angle

Variants of the equation assume equilibrium (no change over time), an approximation of the composite of all Wavelengths (Gray Atmosphere, using the Rosseland Mean Opacity), a directional component (Eddington Approximation) and/or that variation in the medium is in a single direction (Plane-parallel Atmosphere). These are used in models of Stellar Structure.

http://www.met.reading.ac.uk/~ross/Science/RadTrans.pdf

Radiative Transfer (RT)

Source Function (S)