A model for the radiative properties of opaque rough surfaces

We present a theoretical and numerical study of the directional spectral emissivity of an opaque rough surface, when the roughness is in the submicronic range. We establish the equivalence between an approach based on the use of the emissivity at small length scale and an approach based on the Kirchhoff approximation in the framework of electromagnetism. Corrections accounting for shadowing and multiple scattering are included in the model. The result is compared to rigorous numerical simulations using a Monte-Carlo algorithm. The influence of the polarization is put forward. Finally, we discuss the validity of local emissivity at submicronic scale.