radiative transfer

The process by which the energy associated with electromagnetic radiation is transferred as the radiation interacts with matter. In radiative transfer, photons are continually being absorbed and re-emitted by matter. In simple terms, the law of conservation of energy requires that the energy emerging from a medium is equal to the amount entering it, plus any energy emitted by the medium itself but minus any energy absorbed. This can be expressed mathematically, but real solutions are difficult because of the complexity of the way in which matter and radiation interact in practice.