Light scattering from graphite powders - an experimental investigation

The light scattering behavior of powdered surfaces is of fundamental importance in planetary science, remote sensing, aerosol physics, and optical material characterization. Airless planetary bodies such as asteroids and the Moon are covered with regolith, a layer of unconsolidated particulate material whose optical response carries information about surface composition and physical properties. In this work, laboratory-based light scattering measurements are reported for two well-characterized graphite powder samples of different particle size ranges. Graphite is a relevant analog material due to its presence in carbonaceous (B- and C-type) asteroids and its strong optical absorption. Angular-dependent bidirectional reflectance measurements were performed using a goniometric setup described in (Deb 2020) with monochromatic illumination at 535 n m $535~nm$ . The samples were independently characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and particle size analysis (PSA). The resulting scattering phase curves reveal a non-trivial dependence on particle size, a crossover behavior is observed in the reflectance curves, consistent with Kamei and Nakamura (2002) for their graphite samples. at intermediate phase angles. These experimental datasets provide reliable ground-truth inputs for theoretical modeling of light scattering from irregular, absorbing particulate surfaces and are relevant for the interpretation of remote sensing and in-situ spacecraft observations.