In Situ Photometric Experiment of Lunar Regolith With Visible and Near-Infrared Imaging Spectrometer On Board the Yutu-2 Lunar Rover

Abstract

China's Chang'E-4 (CE-4) mission successfully landed in Von Kármán crater within South Pole-Aitken basin of the Moon. The Visible and Near-Infrared Imaging Spectrometer (VNIS) on board Yutu-2 rover investigated the photometric properties of lunar regolith. Seven VNIS measurements were conducted on a small lunar surface with a diameter <5 m by the rover rotating at the center, with the phase angles from 39.6 to 97.1° obtained in the similar observational geometry of solar altitude and observation angle. The phase function, which varies in different wavelength, is derived using a third-order polynomial fitting, in combination with the calibration and comparison of orbital/in situ VNIS data at the Chang'E-4 landing site and the same regions. After the photometrical correction of the spectra with the phase function, the derived FeO contents and optical maturity parameters of the regolith reduce much of their deviations, which is consistent with the homogeneity of the regolith and hence demonstrates the significance of the photometric correction on the VNIS spectra.