Mineral Spectra Extraction and Analysis of the Surface Mineralogy of Mars with Hyperspectral Remote Sensing

The images acquired by the Observatoire pour la Mineralogie, l’Eau, les Glaces et l’Activite (OMEGA) hyperspectral spectrometer on Mars Express of the surface of Mars are affected by noise and large pixel sizes. The stability of the spectra used to identify mineralogy with OMEGA has not been studied in detail across different scenes and spatial resolutions. A modified image processing method and an analysis of correlation between spectra is proposed to evaluate how selected image spectra of key rock-forming minerals relate across different OMEGA image resolutions and to laboratory measurements of mineralogical spectra. The Nili Fossae region at the western edge of the Isidis impact basin on Mars was the area chosen to be studied due to the diverse mineralogy that has been associated with it. Here, spectra were extracted from regions identified with spectral parameters or summary products where groups of rock-forming minerals occurred. Image-extracted spectra were used as endmembers to produce a spectral library with which the statistical method of spectral angle mapping was applied to map the mineralogical distribution in OMEGA images of different resolutions. The extracted spectra were also compared to laboratory spectra via their spectral angles. Results showed low angles and high correlation between the extracted spectra in different resolutions, and relatively low correlation between the extracted spectra and the laboratory spectra. Spectral angle mapping of the images revealed that some spatial coherence of the mapped mineralogy existed, but spectra from the maps were highly correlated for all endmembers. A cross-validation between processed images from OMEGA and the higher resolution Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on NASA’s Mars Reconnaissance Orbiter showed relatively low correlation between their corresponding mineral spectra. Visual identification of mineralogical spectra was more precise at identifying mineral species than summary products were. Extracted spectra were stable across different resolutions but were not identifying precise minerals based on their spectral properties because the chosen summary products are not effective at identifying precise mineralogical spectra. These summary products should therefore be used with care in future mineralogical analysis of Mars’ surface with remote sensing. Spectra behaves stably enough across different resolutions, but with OMEGA, it would be best to use spectral angles to map with a library of minerals confirmed to be present by rovers, the direct sensors on the surface.