Experimental Determination of the Hapke Shadowing Function Parameter for Planetary Regolith Surface Analogs

Introduction: The physics of the process that controls the interaction of light with planetary regolith surfaces is complex and only partially understood. In the past years, a number of semi-empirical models have been developed for analyzing the bidirectional reflectance data of particulate surfaces based on the scattering and absorption properties of minerals and rocks (e.g. [1], [2], [3], [4]). In particular, using the radiative transfer equation describing the scattering of light from soils, Hapke [1] developed an approximate analytical solution, which is widely used for studying reflectance data from planetary surfaces (e.g. [5], [6], [7]). This model is generally difficult to handle because it requires the knowledge of six physical parameters, linked with multiple scattering, phase function, opposition effect, and roughness. This work presents a method for a determination of the global set of parameters involved in Hapke’s model for planetary surface analogs when considering a set of angular conditions representative of the usual range from spaceborne observation in planetary exploration. We focus on the physical meaning of the shadowing function parameter (θ).