Near‐infrared spectral reflectance of mineral mixtures: Systematic combinations of pyroxenes, olivine, and iron oxides

Abstract

Near‐infrared spectral reflectance data are presented for systematic variations in weight percent of two component mixtures of ferromagnesian and iron oxide minerals. Mixtures were chosen for application to the study of the dark materials on Mars, but the results are equally applicable to mafic and ultramafic assemblages elsewhere in the solar system. Olivine spectral features are greatly reduced in contrast by admixture of other phases but remain distinctive even for low olivine contents. Clinopyroxene and orthopyroxene mixtures show resolved pyroxene absorptions near 2 μm. The addition of limonite greatly modifies pyroxene and olivine reflectance but does not fully eliminate distinctive spectral characteristics. Using only spectral data in the 1‐μm region, it is difficult to differentiate orthopyroxene and limonite (goethite) in a mixture. Additional spectral coverage or other evidence may be required for a unique interpretation. All composite mineral absorptions observed in this study are either weaker than or intermediate in strength to the end‐member absorptions and have bandwidths greater than or equal to those for the end‐members. In general, spectral properties in an intimate mixture combine in a complex, nonadditive manner, with features demonstrating a regular but usually nonlinear variation as a function of end‐member phase proportions.

Calibrations of phase abundance, composition, and particle size distribution for olivine‐orthopyroxene mixtures from reflectance spectra

“…An additional 12 spectra of olivine-orthopyroxene, olivine-clinopyroxene, and orthopyroxene-clinopyroxene mixtures and their end-members, which formed the basis for an earlier study [Singer, 1981], were used in a qualitative fashion to indicate the effects of clinopyroxene in the spectra but otherwise were not used in our development of calibrations. All spectra were obtained with the spectrogoniometer of the Planetary Geosciences Division at the University of Hawaii with a halon reflectance standard [Singer, 1981]. In all cases, samples were measured at a phase angle of 15 ø.…”

“…The band I and band II areas were measured using a planimeter and the resulting values were ratioed. The band area ratios, the derived phase abundances, and the stated phase abundances [Singer, 1981] are listed in Table 3.…”

“…The steep drop-off in reflectance shortward of about 0.55 /tm due to charge transfer absorptions [Tossell et al, 1975;Adams, 1975 Singer [1981] have shown that there are consistent variations in spectral properties with phase abundance. In the present paper, we have undertaken a detailed study of the spectral variations of olivine-orthopyroxene mixtures in order to define the systematics of their spectral behavior and to establish interpretive calibrations.…”

Does Independent Component Analysis Play a~Role in Unmixing Hyperspectral Data?

“…ICA finds a separating matrix , such that (13) where is a vector of independent components, and and are permutation and scale matrices, respectively.…”

“…The linear mixing model holds when the mixing scale is macroscopic [12]. The nonlinear model holds when the mixing scale is microscopic (or intimate mixtures) [13], [14]. The linear model assumes negligible interaction among distinct endmembers [15], [16].…”