Reflectance Spectra of Andesitic Rocks: Comparison between Chemical and Mineralogical Information.

Abstract

The knowledge of the mineralogical and chemical composition of planetary surfaces is essential for evaluating differentiation and alteration processes. For this purpose, the most useful remote sensing technique is spectrophotometry in the visible and near infrared. Spectrophotometric analyzing techniques are based on laboratory spectra. Quantitative methods require statistical procedures like principal component analysis. Most studies so far have focused on the determination of the mineralogy. Recently the spectrophotometric analysis of lunar data is used for a quantitative estimation of chemical parameters. Proceeding from these results we performed laboratory measurements from 0.5-2.5 ym in order to compare the relation between reflectance spectra and chemical and mineralogical components, respectively. Andesitic rocks are considered as a probable analogue for martian material. The spectral signatures are dominated by absorption features due to Fe2+, Fe3+, and the OH--ion. For comparison, the spectra were fitted as a multiple linear regression of the chemical and mineralogical composition. The chemical influence dominates at 0.7-1.6 and 0.6 ym. At longer wavelengths the minaralogy becomes more prominent. PCA analysis was performed for different wavelength ranges. The spectral characteristic of eigenvectors for higher order eigenvalues can be attributed to compositional constituents. The relation of principal components with chemical and mineralogical constituents is tested.