Modelling radiative mean absorption coefficients

We define and compute mean absorption coefficients for the macroscopic models of radiative transfer. These coefficients take into account the anisotropic form of the photon emission and lead to a better computation of a photonic flow far from the radiative equilibrium. They are deduced by averaging a specific radiative intensity on the space of frequency and are generalized versions of the Planck means. This intensity is obtained by minimizing the mathematical entropy with the constraint of the reconstruction of radiative moments and constitutes the closure of the M ₁ radiative model. We discuss the influence of these coefficients, extend them to the case of multi-frequency problems and perform a numerical comparison with the former Planck mean.