Effect of Lunar Complex Illumination on In Situ Measurements Obtained Using Visible and Near-Infrared Imaging Spectrometer of Chang’E-4

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.

In‐Situ Photometric Properties of Lunar Regolith Revealed by Lunar Mineralogical Spectrometer on Board Chang’E‐5 Lander

“…Some bright spots that were probably produced by stray light were also observed (Figure 1d). Shadows and stray light affect the spectral data to a certain extent (J. Xu et al., 2021). The areas with rocks, shadows, and bright spots were excluded when performing photometric model fitting.…”

“…Shadows and stray light affect the spectral data to a certain extent (J. Xu et al, 2021). The areas with rocks, shadows, and bright spots were excluded when performing photometric model fitting.…”

Dark blue-green: Cave-inhabiting cyanobacteria as a model for astrobiology

“…That could be compatible with cyanobacterial life. Due to the fact, that materials such as regolith and basalts show an increased reflectivity in the red/IR region (Anbazhagan and Arivazhagan, 2009;Gaier et al, 2012;Xu et al, 2021), a FR enrichment analogous to Earth caves could be expected. Similar features (Sauro et al, 2020) and materials (Mandon et al, 2022) can be found on Mars, whose caves might also present a more hospitable environment than the surface (Léveillé and Datta, 2010;Irwin and Schulze-Makuch, 2020).…”

Radiative Transfer Modeling of Chang’e-4 Spectroscopic Observations and Interpretation of the South Pole-Aitken Compositional Anomaly

“…An artifact absorption around 820 nm (Figure A2) is noticed in VNIS spectra and is probably caused by the F46 films in the multilayer insulation (Xu et al 2021) on the body and/or aluminum metal in the wheels of the Yutu-2 rover. This artifact is more obvious in VNIS spectra of darker pixels where the sunlight is shielded by local topography while the reflected and/or scattered sunlight with 820 nm absorption from the rover serves as a dominant light source.…”