In this work is described a hybrid numerical code aiming to retrieve the thermal radiative properties of opaque heterogeneous coatings. The code is based on the combination of a Monte Carlo Ray Tracing (MCRT) program and of the use of the Effective Medium Approximation (EMA). This hybrid code is able to takes account for the surface roughness, the internal porosity and the chemical composition of a given layer. The solid part of a coating is composed of a conducting oxide which contents excess oxygen (δ ∼ 0.1–0.2). Due to δ and to their thicknesses (> 2 μm), the coatings are opaque for the spectral range going from the far infrared range to the visible range. For each layers, their normal spectral emissivity have been measured by infrared spectrometry (T ∼1000K). The comparison of the numerical spectra to the experimental ones permits the discussion of the effects of both the surface roughness, and the internal porosity on the emissivity spectra.

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