Chang'E‐5 In Situ Spectra Reveal Photometric Properties of the Lunar Surface

Abstract

The Chang’E‐5 (CE‐5) lunar mineralogical spectrometer (LMS) obtained an in situ multiangular spectral data set, with which this work aims to study the photometric properties of the lunar surface in the CE‐5 sampling area. We first converted the LMS Level 2B radiance data to reflectance, and then spliced it and processed thermal correction. We also used a millimeter‐scale digital elevation model (DEM) to re‐calculate local illumination and observation conditions considering the high‐resolution topography at the landing site. We analyzed the multiangular reflectance data set with a Hapke modeling approach aimed at characterizing the scattering properties of the surface. In particular, we found that the surface exhibits a spectral signature typical of mafic materials and is close to the mature mare lunar soil. The position of the in situ photometric parameters in the hockey stick diagram indicates that CE‐5 lunar soil particles are forward scattering, irregular and with a low density of internal scatters. Furthermore, we found that all the in situ data (including CE‐3/4/5) and laboratory measurements exhibit forward scattering properties, but the orbiter remote sensing measurements are backward scattering. We attribute this discrepancy to the different resolution of the two data sets: the in situ analysis focuses on the individual particles, whereas remote sensing approach is sensitive to the particle complex. The Hapke parameters we derived can provide a reference for the further comprehensive analysis of remote sensing and in situ spectral data, especially, caution is advised when applying the photometric parameters derived from in situ or laboratory spectra to the remote sensing data.