RadiativeTransferAnsätzen

Radiative transfer is the study of how electromagnetic radiation propagates through a medium, taking into account absorption, emission, and scattering by matter. It provides a quantitative framework for predicting how light is attenuated and modified as it moves through atmospheres, interstellar dust, stellar interiors, or planetary surfaces.

The core of the theory is the radiative transfer equation, which describes the change of the specific intensity Iν along a path s. In its simplest form, dIν/ds = -κν Iν + jν, where κν is the absorption coefficient and jν is the emission coefficient. When scattering is important, additional terms describe in-scattered light, and the equation is often expressed in terms of optical depth τ and a source function Sν such that dIν/dτν = Iν - Sν. Solving these equations requires specifying geometry, boundary conditions, and the radiative properties of the medium.

Solutions commonly rely on numerical methods for complex systems. Techniques include the discrete-ordinate and Feautrier methods for deterministic solutions and Monte Carlo simulations for probabilistic transport, with adaptations for isotropic or anisotropic scattering and for nonlocal thermodynamic equilibrium conditions in plasmas and stellar atmospheres.

Applications span astrophysics, atmospheric and climate science, and remote sensing. In astronomy, radiative transfer models explain stellar spectra and the appearance of galaxies and exoplanets. In Earth's atmosphere, they underpin climate forcing, weather forecasting, and satellite retrievals of temperature, humidity, and aerosol content.

Historically, radiative transfer emerged in the early 20th century and has been developed through work by Eddington, Milne, Chandrasekhar, and others. It remains a foundational tool in interpreting observed radiation across many disciplines.