Characterization of the multiscale roughness of natural volcanic surfaces: effects on their photometric behavior

Surface roughness is a key physical parameter of soils that controls many surface processes and that influences the scattering of incident electromagnetic waves at a wide range of scales. B. Hapke formalized a photometric model providing an approximate analytical solution of the Bidirectional Reflectance Distribution Function (BRDF) of a particulate medium: he introduced the effect of surface roughness as a correction factor for the BRDF of a smooth surface. This work aims to better understand the relative influence of multiscale roughness on soil BRDF and to test the ability of the Hapke model to retrieve a roughness parameter that depicts well the ground truth using very high resolution topographic data of volcanic surfaces of the Piton de la Fournaise and ray-tracing simulations.