Sunlight incident parallel to the moon is reflected by the surface material and enters Visible and Near-infrared Imaging Spectrometer (VNIS) of Chang’e-4. The raw data undergoes a series of preprocessing procedures to generate VNIS 2B radiance data. However, the obtained radiance also varies with viewing geometry (the incidence angle, emission angle and phase angle), resulting in difference in reflectivity conversion, identification inversion of mineral composition and so on, which is not conducive to the scientific interpretation of the mineral composition on the lunar farside. In order to eliminate the influence of solar illumination-observation geometry, a photometric model describing the changes of the lunar surface radiance with the angle of incidence, emission and phase angle must be established. Chang'E-4 is the first visible and near-infrared in-situ exploration on the lunar farside, the establishment of its photometric model could provide an opportunity for in-depth research on the photometric properties of the lunar farside.

In this study, the Lommel-Seeliger (LS) model and Hapke radiative transfer (Hapke) model was used, combing with the photometric experiment conducted on the 10th lunar day of Chang'E-4. Photometric models’ parameters of each band were fitted respectively. The research results show that after photometric correction, the spectrum of the same target exhibits good consistency. What’s more, linear relationship between the number of shadow pixels and reflectance is observed, revealing the influence of surface roughness on visible and near-infrared detection.

Research published in the 51st Lunar and Planetary Science Conference "Lunar and Planetary Science Conferences"

Link: https://www.hou.usra.edu/meetings/lpsc2020/pdf/1921.pdf

Qi, X. B., Zhang, J., Ling, Z. C., Chen, J., Liu, C. Q., Liu, L., ... & Xu, R. (2020). Photometric Correction of the Chang'E 4 Visible and Near-Infrared Imaging Spectrometer (VNIS) Data. LPI, (2326), 1921.