The photometric properties of the uppermost lunar regolith are used in the spectroscopic study. China's Chang’E‐5 (CE‐5) mission successfully landed in the Northern Oceanus Procellarum of the Moon, carrying the scientific payload lunar mineralogical spectrometer (LMS). LMS performed full‐view scanning and obtained the reflectance spectra in various geometric configurations. The photometric properties, including the single‐scattering albedo ω and two parameters of the Henyey‐Greenstein phase function (b, c), were derived. Our modeling results showed weak backward scattering and strong forward scattering properties of the regolith at the CE‐5 landing site. Meanwhile, the asymmetry parameter indicates that CE‐5 regolith has weaker forward scattering than the Apollo lunar soil samples and the regolith at the Chang’E‐4 landing site. The derived Hapke parameters can be used for comparison with that of the returned lunar sample, supporting further studies of lunar spectroscopy, and can be the ground truth of the CE‐5 landing area.

In-situ measurements of the spectral information on the lunar surface are of significance to study the geological evolution of the Moon. China’s Chang’E-4 (CE-4) Yutu-2 rover has conducted several in-situ spectral explorations on the Moon. The visible and near-infrared imaging spectrometer (VNIS) onboard the rover has acquired a series of in-situ spectra of the regolith at the landing site. In general, the mineralogical research of the lunar surface relies on the accuracy of the in-situ data. However, the spectral measurements of the Yutu-2 rover may be affected by shadows and stray illumination. In this study, we analyzed 106 CE-4 VNIS spectra acquired in the first 24 lunar days of the mission and noted that six of these spectra were affected by the shadows of the rover. Therefore, a method was established to correct the effects of the rover shadow on the spectral measurements. After shadow correction, the FeO content in the affected area is corrected to 14.46 wt.%, which was similar to the result calculated in the normal regolith. Furthermore, according to the visible images, certain areas of the explored sites were noted to be unusually bright. Considering the reflectance, geometric information, and shining patterns of the multi-layer insulation (MLI), we examined the influence of the specular reflection of the MLI on the bright spot regionsd, and found that the five sets of data were likely not affected by the specular reflection of the MLI. The results indicated that the complex illumination considerably influences the in situ spectral data. This study can provide a basis to analyze the VNIS scientific data and help enhance the accuracy of interpretation of the composition at CE-4 landing sites.

The Visible and Near-infrared Imaging Spectrometer (VNIS) is one of the scientific payloads onboard the Yutu-2 lunar rover of the Chang’E-4 mission. Based on Acousto-Optic Tunable Filter (AOTF) dispersion, a moving platform and a calibration unit, the VNIS was designed for lunar surface observations of the far side of the Moon for composition exploration and spectral experiments in the wavelength range of 0.45–2.4μm. Large differences in radiance caused by the discrepancy between the laboratory and lunar environment could affect the spectral shape and features. Therefore, in-flight calibration of the VNIS is critical for the interpretation of the acquired spectra. To precisely map the digital output to the spectral radiance, a calibration unit was installed on the VNIS to facilitate radiometric calibration measurements on the lunar surface. After the elimination of stray light and the shadow effect, the measured radiance of the calibration unit was derived by digital multiplication of the pre-flight coefficients. Considering the observation geometry, Moon-Sun distance, and the bi-directional reflectance factor (BRF) of the calibration panel, the theoretical radiance at the entrance pupil of VNIS was calculated. Using linear regression, in-flight calibration of the coefficients was performed and used to correct the spectral data. The performance of the spectrometer was evaluated using 12 lunar-day data. It was determined that the coefficients gradually converged and the variation was less than 1%, indicating that the in-flight calibration was robust. The proposed in-flight calibration method facilitated the acquisition of reliable data for lunar composition interpretation.