Investigating Lunar Surface Photometric Properties in the Near-Infrared with LOLA

The photometric properties of the Moon can reveal important clues to geological and space weathering processes operating on the lunar surface and airless planetary bodies, in general. Such processes can affect the surface reflectance behavior with wavelength and viewing/illumination geometry by altering the scattering properties of the regolith particles and the structure of the regolith surface. Here we present new results investigating the spatially-resolved near-infrared phase function behavior over the lunar surface as measured by the Lunar Orbiter Laser Altimeter (LOLA) aboard the Lunar Reconnaissance Orbiter (LRO). Since December 2013, LOLA has been collecting photometric measurements of reflected sunlight at a wavelength of 1064-nm making it the longest-running narrow-band near-infrared passive radiometer ever to orbit the Moon. Incorporating the zero-phase, actively-derived, normal albedo measured by LOLA reveals phase function trends and photometric anomalies, which we interpret in the context of space weathering and geological effects on the micro-structure of the surface and scattering particles. The LOLA 1064-nm passive radiometry can also probe permanently shadowed regions (PSRs) with scattered light from nearby illuminated terrain, potentially offering a new tool to search for differences in albedo between PSRs and non-PSRs. As LRO's orbit evolves, the phase angle and spatial coverage of LOLA's passive radiometry will continue to expand allowing even more detailed and comprehensive photometric studies with this unique dataset.