A Monte-Carlo radiative transfer model to simulate thermal infrared emission spectra from planetary surfaces: Mineralogical mixtures and thermal gradients

Thermal IR spectroscopy has been widely used in the exploration of the Solar System to characterize the mineralogical composition of planetary surfaces. Beyond the identification of the different compounds, estimating their abundances presents significant challenges, hence the usual application of simplified models that generally assume linear mixtures for example. These approaches, relatively easy to use, might however lead to important biases. Here we present a novel model based on a Monte-Carlo approach to compute the radiative transfer within a granular medium where the grains are resolved. A critical aspect of our model is that it can more directly accept data acquired from lab experiments to simulate various types of mixtures (linear, intimate, layered) in a realistic manner. Variable thermal profiles can also be simulated in the sample. Such a model can be used to better constrain the abundances of mineral compounds in natural planetary surfaces. We present some first applications, in particular estimating potential biases when neglecting multiple scattering in the models. We also evaluate the effect of porosity and thermal gradients in a few limited cases to prove the feasibility for future applications.