Four-flux model for a multilayer, plane absorbing and scattering medium: application to the optical degradation of white paint in a space environment.

We generalize the four-flux radiative transfer model to the case of a multilayer medium. A concrete application, that of the study of the optical degradation of white paint in a simulated space environment, is presented. The degraded material is decomposed in a damaged layer and in an unaffected layer, and we assume that the degradation is due to a variation Dkappa of the imaginary part of the refractive index in the damaged layer. Then we find an empirical law for variation Dkappa with dose, taking into account possible saturation.