Abstract
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.
Highlights
Based on the laboratory test data and in-situ geometric angle and spectral data, we investigated the effect of the multi-layer insulation (MLI) specularly reflected solar radiation and rover shadow on the visible and near-infrared imaging spectrometer (VNIS) data
It was noted that the VNIS will be affected by the MLI and shadow at a specific angle, owing to which, the reflectance of the affected area is significantly different from that of the normal area
We performed laboratory tests and in-flight data validation to demonstrate that the complex illumination in the lunar environment, including the shadows of the rover, affect the spectra data of the VNIS
Summary
Researchers have focused on CE-3 VNIS data that in-situ detection can be constrained by the observation angles and surface roughness and unevenness, resulting in significant small-area shadow effects [10]. (b) Light paths of bright spots introduced by MLI specular reflection Considering these aspects, in this study, the data obtained by the VNIS and method to calculate the reflectance factor (RADF) [12] were considered. We proposed a method to determine whether the bright spot areas were affected by stray illumination introduced by the specular reflection of the MLI by considering the reflectance, geometric information, and shining patterns of the MLI
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