Phase function parameter c against b. The parameter values of the four datasets are the mean values with a standard variation values across all points, after excluding abnormal points. The upper and lower limits constrain the reasonable parameter space (Hapke 2012a). The orbital research results of highland immature ejecta, highland mature soil, and mare mature soil are from Sato et al. (2014). The laboratory research results of Apollo 16 and 11 soil samples are from Johnson et al. (2013). The in situ research result of the CE-5 Lunar Mineralogical Spectrometer (LMS) is from Xu et al. (2022a), and that of the CE-3 and CE-4 PCAM inverted by the five-parameter Hapke model are from Jin et al. (2015) and Jiang et al. (2021), respectively.