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Titel |
Mixing of surface materials investigated by spectral mixture analysis with the Moon Mineralogy Mapper |
VerfasserIn |
Jean-Philippe Combe, Thomas B. McCord, Georgiana Y. Kramer, Carle M. Pieters, Lawrence A. Taylor, Joseph W. Boardman, John F. Mustard, Jessica M. Sunshine, Stephanie Tompkins, Robert O. Green |
Konferenz |
EGU General Assembly 2010
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 12 (2010) |
Datensatznummer |
250038007
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Zusammenfassung |
Mapping of surface units on the Moon, as well as identification and quantification of
mineralogical components is the main task of the imaging spectrometer Moon Mineralogy
Mapper (M3) [1] onboard Chandrayaan-1. In spectral analysis, mixing of surface materials
need to be considered because they may have implications for the interpretation of the
lithology. Materials that are juxtaposed within the field of view result on linear combinations
of reflectance spectra [2]. Lateral contamination by remote components [e.g. 3,4], minerals in
a rock [5,6], coatings [e.g. 7-9] and adjacency effects due to scattered light [10], are
non-linear processes. In the present study, we perform linear Spectral Mixture Analysis
(SMA) [11] using the Multiple-Endmember Linear Spectral-Unmixing Model (MELSUM,
[12,13]) that allows limiting the number of components used in a model and guarantees
positive mixing coefficients, and the sum of the mixing coefficients constrained to
one. We use MELSUM both for spectral endmembers selection and to produce
corresponding image fractions. This method is convenient for an initial assessment of large
data sets [13] prior to using more quantitative methods for compositional analysis
[5,6].
We have used a mosaic of all M3 images that cover ~80% of the surface and 10-20 nm
spectral sampling. In order to avoid the effects of thermal emission, the analysis is performed
in the range 0.4-2.18 μm (65 channels). A sphere-based Lommel-Seeliger photometric
correction has been performed to standardize the effects of the geometry of illumination at
large scale [14].
From a global scale, resulting spectral endmembers describe the most abundant
components at the surface of the Moon: Anorthosite, high-calcium pyroxene (HCP),
low calcium pyroxene (LCP) and olivine. Plagioclase-rich soils (anorthosite) are
detected in the highlands, especially in the south hemisphere, with few spots in fresh
impact craters (e.g. Copernicus). HCP and olivine are highly correlated with the mare
basalts. However, spots are found also in fresh impact craters (e.g. Aristillus for HCP,
Tycho, for LCP, Aristarchus for olivine) where exposed materials are likely crustal.
Olivine fraction is weak but it defines a homogenous unit in Oceanus Procellarum
and Mare Imbrium, around Aristarchus. Low fractions of mature soils indicate the
locations of fresh impact craters. Overall, these spatial distributions are similar
to the mineralogical maps obtained by [15] using a radiative transfer model on
Clementine data, although image fractions are simply indicators of relative detections of
minerals.
Further development will be focused on more detailed descriptions of the lithology,
mixing processes, and quantitative estimate of the surface maturity of the various lunar soils.
In theory, image fractions represent areal mixtures of materials. A step forward will be the
use of a radiative transfer model to calculate more accurate abundances of minerals
from the spectral endmembers, and then to derive mineral maps from the image
fractions.
References: [1] Pieters et al., 2009, LPICo # 6002. [2] Singer and McCord,
1979, 10th LPSC 1835-1848. [3] Shoemaker 1962, Phys Astron Moon 283-380. [4]
Pieters et al., 1985, JGR, 90. [5] Hapke 1981, JGR 86. [6] Shkuratov et al., Icarus
137. [7] Adams 1973, Science 171. [8] Cassidy and Hapke, 1975, Icarus 25. [9]
Lucey et al. 2000, JGR 105. [10] Sanders et al., 2001, RSE, 78. [11] Adams et al.,
1986, JGR, 91. [12] Combe et al., 2008, PSS 56. [13] Combe et al., 2008, 39th
LPSC 2247. [14] Hapke and Van Horn, 1963, JGR 68. [15] Lucey 2004, GRL 31. |
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