On the eve of a new era of human exploration, the promise of new Lunar surface observations (Chang’e and other robotic missions) begs for a thorough review of our understanding of how reflectance and polarization phenomena are related to the microproperties of regolith. During the Apollo era, remotely-sensed reflectance and polarization observations of the Moon were compared with laboratory measurements. Ultimately such efforts led to new understandings of physical processes of electromagnetic radiation as it is scattered in particulate media. Specifically, two distinct radiative scattering processes called ‘shadow hiding’ (SH) and ‘coherent backscattering’ (CB) (Hapke et al., 1993) have been shown to rely upon the size, sorting, and shapes of materials comprising planetary regolith.
Because the shapes of the reflectance and polarization phase curves are influenced by the microproperties of the regolith material, we might better understand the surface characteristics of distant solar system objects by measuring their near-opposition reflectance and polarization behavior from Earth or near-Earth orbit (Nelson et al., 2018). Profound advances in laboratory techniques have occurred since these original 1993 measurements. Foremost among these is the utilization of the reciprocity principle, established by Helmholtz in 1856, which significantly improves signal-to-noise as demonstrated in our advanced Goniometic Photopolarimeter (GPP) design (Nelson et al., 2018).
Hapke et al. (1993) measured the photometric properties of eight Apollo samples. We have been approved by NASA to re-measure the same samples with our modernized GPP. This additional foundational basis will enhance the value of the samples and data returned by the Chang’e and other missions. It also opens the possibility of understanding regolith microtextures from remote-sensing data.
Hapke, B, W. et al., Science, 260, 509, 1993.
Nelson, R. M. et al., Icarus, 302, 483, 2018.