A method to assess the applicability and accuracy of the Modified Gaussian Model (MGM) on the rock samples’ spectral interpretation.

Abstract

Abstract The Chang'e-4 mission obtained spectral data of multiple rock targets on lunar surface. The MGM is usually applied to the spectral interpretation of powder samples, its applicability and accuracy on the rock targets remain to be further evaluated. The rock slice of lunar meteorite NWA4734 is used to conduct comprehensive analysis of the petrography, mineralogy and laboratory spectroscopy, which will provide important ground truth for the MGM interpretation of lunar in-situ spectra of rock samples. Firstly, Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometer (EDS), and Electron Probe Micro-Analyzer (EPMA) analysis results indicate that: (1) almost all plagioclase in NWA4734 have been converted to maskelynites, which indicate that the meteorite has undergone severe impact metamorphism; (2) the chemical composition of pyroxene and olivine is significantly heterogeneous, showing a distribution characteristic of magnesium-rich core and iron-rich rim, further indicating that NWA4734 has undergone multiple crystallization and differentiation. Secondly, this article focuses on the rcok slice of NWA4734’s greyscale image of the Back Scattering Electron (BSE), and obtains the proportion of High Calcium Pyroxene (HCP) in the total pyroxenes of this sample by calculating the area percentage using pixels counting method. The result shows that the proportion of HCP is 72% ± 5.4%, which can be used as a ground truth to evaluate the interpretation applicability and accuracy of MGM. A Field Spectrometer (ASD) is used to measure the visible and near-infrared reflectance spectra (450-2500nm) of the rock slice from NWA4734 in the same area as the BSE image obtained by SEM, and MGM is used to deconvolve the ASD spectra, and the average proportion of HCP is estimated to be 71%±10.1%. The results between the MGM and the pixels counting are comparable within the error range, which proved the applicability of MGM on interpretation of the rock samples on lunar surface.