Mineral abundance and particle size distribution derived from in situ spectra measurements of the Chang’E-3 Yutu rover

Abstract

An important issue in planetary exploration and sciences is the determination of mineral abundances and particle size distributions from visible – near-infrared spectra. Such analyses can help elucidate which geological processes have been active on the surfaces of the Moon and planets. The imaging spectrometer on board the Yutu rover of the Chang’E-3 mission measured the reflectance spectra of lunar soil at a height of approximately 1 m, providing new insights into the lunar surface. A new method combining a Hapke radiative transfer model and the sparse unmixing algorithm was proposed to retrieve the mineral abundance and particle size distribution and applied to the in-situ measurements from the Yutu rover. The imaginary part of the refractive index of each endmember was first calculated by solving the Hapke model. The single-scattering albedos of each endmember with different particle sizes were then obtained based on the Hapke slab model, allowing the construction of an endmember library. The single-scattering albedos of mineral mixtures, which were computed using the Hapke bidirectional equation, were then unmixed using the sparse unmixing algorithm with the aid of the endmember library. Laboratory measurements obtained from the Reflectance Experiment Laboratory were used to validate the proposed methodology. The results revealed that the methodology exhibits a good performance in retrieving the mineral abundances and particle sizes from mixtures. Finally, the methodology was applied to the Yutu rover measurements. At one of the locations, Node E, the agglutinate abundance was 71% and the abundances of both clinopyroxene and olivine were approximately 10%. The particle size distributions of each mineral exhibited almost normal distributions with different mean particle sizes and variance, possibly indicating the distinct responses of each of the components at this site to space weathering.