The generalized Eddington approximation in radiative transfer

The anisotropy of the radiation field, which causes the flux, is directly related to the geometry of the system. The angular parameters characterizing the anisotropy are introduced for the general and axially symmetric systems. The mean intensity, three components of the flux vector, and five angular parameters constitute nine independent variables and the corresponding nine transfer equations are formulated for the general case. The number of independent variables (or quantities) is reduced to six for the axially symmetric case. Further specification of the geometry reduces the treatment to the case of Unno and Kondo (1976) for the spherically symmetric system and to the usual Eddington approximation for the plane-parallel system. (author)