In situ optical measurements of Chang'E-3 landing site in Mare Imbrium: 2. Photometric properties of the regolith

The panorama cameras onboard the Yutu Rover of the Chang'E-3 lunar mission acquired hundreds of high-resolution color images of the lunar surface and captured the first in situ lunar opposition effect (OE) since the Apollo era. We extracted the phase curve and the color ratio in three bands with the phase angle range from 2 degrees to 141 degrees. Photometric inversions using the Hapke model reveal that submicroscopic dusts are present in the landing area and both the coherent backscattering and the shadow hiding are responsible for the strong OE. Compared with spaceborne measurements, the grains in the landing site are brighter, more transparent, and appear to be better crystallized than the average maria basaltic grains. The results show that the phase-reddening effect appears to be present in the in situ phase curves. The current phase curve can be used as the ground-truth validations of any future spaceborne phase curve measurement over the landing site region.