Selection of base spectra from small mare craters adjacent to the CE6 landing site. We specifically utilized the relatively immature crater C4—located in close proximity to the CE6 landing site—for our analysis. This spectral dataset was derived in previous studies and sourced from X. Lu et al. (2025). (a) Relative positions of the C4 crater and the CE6 landing site, both situated within the western mare region south of the Apollo basin. The background is an M³ 750 nm reflectance base map (image ID: M3G20090717T211502). (b) The spectra of craters (M³) and the CE6 landing region (LMS, see Table A1). In this figure, we can clearly see that as the regolith on the lunar surface gradually matures, the spectral reflectance continuously decreases, and the overall spectrum tends to flatten.