矿物的种类与含量可限定其形成时特定的地质环境，因此火星表面矿物识别和丰度反演研究对了解火星的地质构造及历史演变过程具有重要意义。Eberswalde撞击坑具有复杂的水文系统，是火星探测的热点地区，而对该地区大范围矿物反演则鲜有研究。基于紧凑型侦查成像光谱仪（CRISM）目标探测模式数据和CRISM光谱库，首先，通过高光谱数据子空间识别算法（Hysime）分析CRISM数据信号子空间，并将光谱库所有矿物光谱投影到子空间上，保留投影误差较小的光谱作为约简后的端元光谱库；然后，使用协同稀疏解混对Eberswalde撞击坑西北部三角洲地区的矿物丰度进行定量反演，得到5种原生矿物：辉石、橄榄石、斜长石、菱铁矿、硬水铝石和1种蚀变矿物透闪石，并从矿物光谱、分布分别对反演结果进行验证；最后，从矿物学的角度对可能成因做出解释，推测该区域存在接触变质作用。

The type and content of minerals can constrain the specifically geological environment where they form. Therefore, studying the identification and abundance retrieval of minerals on Martian surface is essential in understanding the geological structure and historical evolution of Mars. Eberswalde Crater, a hotspot of Mars exploration, possesses a complex hydrological system. However, the large-scale mineral retrieval in this region has rarely been studied. Hence, we used hyperspectral technology to quantitatively retrieve the mineral abundances in the delta region of Eberswalde. Furthermore, we analyzed the geological environment that possibly existed at that time on the basis of the distribution and content of minerals.
This study adopted a sparse unmixing algorithm to quantitatively retrieve mineral abundances by using Targeted Reduced Data Records (TRDR), which are obtained by Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), together with the CRISM spectral library. However, the high mutual coherence of spectral libraries limits the performance of sparse unmixing because the equation to be solved is ill conditioned and time consuming. Therefore, we used the hyperspectral signal identification by minimum error (Hysime) algorithm to analyze the signal subspace of CRISM data. All the mineral spectra of the spectral library were projected onto the subspace. The spectrum with small projection error was then retained as the endmember, which truly contributed to the observed mixtures. Finally, a collaborative sparse unmixing algorithm was applied to CRISM to retrieve the mineral abundances of the delta region in Eberswalde.
The abundance maps show five types of primary minerals (pyroxene, olivine, plagioclase, siderite, diaspore) and one type of alteration minerals (tremolite). Pyroxene is mainly distributed in front of the alluvial fan. Olivine is distributed (east-west) in the central area. Plagioclase is mainly distributed in the western delta region and a small crater edge in the northeastern corner. Siderite, with relatively less content, is mainly distributed along the edge of the alluvial fan. Diaspore is mainly distributed along the river valley, and the relatively enriched diaspore in the northeastern corner was probably caused by the transportation of liquid water in the past. Tremolite is distributed in the northeastern corner of the delta region. We identified a similar trend in both curves by comparing mineral spectra obtained from images with correspondent spectra in the spectral library. The result of the unmixing was consistent with the mineral distribution in the spectral index map, as shown by the comparison of the abundance maps of the three main minerals, namely, plagioclase, pyroxene, and olivine, and the correspondent spectral index map, thereby showing the effectiveness of the inversion results in this study.
A collaborative sparse unmixing algorithm was used to quantitatively retrieve the mineral abundances of the delta region in Eberswalde. Six types of minerals were found, namely, pyroxene, olivine, plagioclase, siderite, diaspore, and tremolite. From the perspective of mineralogy, the instability of pyroxene and olivine indicated that the area where they are distributed is close to provenance and the original provenance is ultrabasic rock (e.g., peridotite) and basic rock (e.g., gabbro), respectively. The existence of tremolite and siderite indicated metasomatism between the rich water and the carbon dioxide fluid in this area. The minerals in the area of the alluvial fan were distributed outside the alluvial fan by fluid transportation. The presence of tremolite in the northeastern corner of delta region reflected the existence of contact metamorphism before the alluvial fan.