基于嫦娥四号就位光谱探测数据的月球背面巡视区矿物丰度反演研究

The Chinese lunar mission Chang’E-4 (CE-4) has been successfully explored the far-side South Pole-Aitken (SPA) basin and obtained Visible and Near-Infrared spectra of lunar soil, providing a new insight to understand the mineral compositions of far-side lunar soil and the possible compositions of lower crust and upper mantle. However, it is a challenge to retrieve the mineral abundance of lunar surface based on the in-situ measured spectra data because of the problems including the severe mixture of mare basalts and ejecta in the landing area, the complicated spectral response mechanism of minerals on lunar surface and the great effects of space weathering. This project will study the selection method of endmember spectra based on sparse expression and the nonlinear spectral unmixing model and algorithm to retrieve the mineral types and abundance at the exploration area of Chang’E-4 rover. We will also study the geological setting of study area and analyze the origin of the materials together with the results of Chang’E-4. At last, we will discuss the possible composition of lower crust or upper mantle. This project could provide key clues and evidences for revealing the history of impact and/or volcanic activity on lunar far-side, deepening our understanding of the Moon's internal composition and early evolution processes.

我国嫦娥四号探测器成功实现在月球背面的南极-艾肯盆地巡视，并近距离获取了月表的红外成像光谱数据，为了解月球背面物质成分及可能的下月壳/上月幔成分提供了新的视角。但是由于巡视区月海玄武岩与撞击溅射物混杂严重、月表矿物光谱响应机制复杂、月壤太空风化严重等问题，使得基于就位光谱探测数据反演月表矿物丰度存在端元光谱难以确定、反演模型构建及求解复杂等挑战。本项目将研究基于稀疏表达的端元光谱选择方法及非线性光谱解混模型和算法，反演嫦娥四号巡视区矿物类型和丰度，并结合对巡视区地质背景的研究，分析物质成分来源，探讨可能的下月壳/上月幔成分，为了解月球背面撞击活动和/或火山活动历史、深化对月球内部成分和早期演化过程的认识提供关键线索和证据。

2019年1月3日，我国“嫦娥四号”探测器在月球南极-艾肯盆地的冯·卡门撞击坑成功着陆，并进行巡视探测，实现了人类首次在月球背面的就位探测。月球车上搭载了红外成像光谱仪、全景相机等有效载荷，获取了大量月表原位观测数据。本课题对嫦娥四号光谱数据进行了细致标定和处理，首次推导出了覆盖可见光-近红外全谱段的原位关键光度参数，厘清了月壤的光度特性；研究了光照和观测角度对光谱的影响并提出校正模型，且定量评估了测量噪声对光谱数据的影响，为后续数据分析打下坚实基础；基于校正后光谱数据通过解混反演出了着陆区物质是含橄榄石的苏长岩，结合地质背景分析，提出着陆区物质来自于月球的深部，很可能是在撞击形成的岩浆湖中经分异结晶而形成，这是首次对月球深部物质组成进行了限定，对理解月球的形成与演化至关重要；通过对全景相机和光谱数据的全面分析，首次原位发现较为纯净的撞击玻璃，并揭示出了月壤形成机制中的关键过程，拓展了对月球表面过程与演化的认识；利用同一月昼对月表同一目标的连续观测数据建立了月表原位光谱数据的热校正模型，并基于此校正了嫦娥五号原位光谱，进而首次提供了月表水存在的原位证据。研究成果在National Science Review、Science Advances、Geophysical Research Letters、Astronomy & Astrophysics、Journal of Geophysical Research: Planets等行星科学领域SCI期刊发表论文8篇。