Fig. 1. Solar elevation angle distributions. (a) Variation of solar elevation angle over time in polar regions; (b) comparison of solar elevation angles at landing sites of the Chang'e mission series

Fig. 2. Average illumination distributions at the lunar south pole^[13]. (a) Image of the lunar south pole captured by LRO camera; (b) illumination rate distribution

Fig. 3. Seasonal thermal radiation temperature distributions above 80°S at the lunar south pole^[14]. (a)(b) Nighttime local time (00:00—01:00); (c)(d) daytime local time (12:00—13:00)

Fig. 4. Comparison of spectral irradiance at the landing zones of the Chang'e-4 and Chang'e-8 missions. (a) Solar spectral irradiance AM0 curve at the Earth's exoatmosphere; (b) emitted spectral radiance curves; (c) total spectral radiance curves; (d) ratio of total spectral radiance between Chang'e-4 and Chang'e-8 landers

Fig. 5. Comparison of spectral radiance among different targets

Fig. 6. VNIS dual-channel signal-to-noise ratio curves

Fig. 7. Infrared spectrometer detection chain and physical component schematics^[8]. (a) Schematic of signal transmission chain; (b) Chang'e-5 lunar mineral spectrometer physical prototype and 3D model diagram

Fig. 8. Comparison of signal-to-noise ratio before and after optimization