Discrimination between maturity and composition of lunar soils from integrated Clementine UV-visible/near-infrared data: Application to the Aristarchus Plateau

Research areas:
APR 25
The reflectance spectrum of a lunar soil is mainly dominated by the
composition and the degree of exposure to space weathering processes
such as micrometeorite bombardment and solar wind implantation. The
spectral alteration effects of space weathering should be removed for
accurately investigating the composition of the lunar surface using
remote sensing data. In this paper we show that the integration of the
Clementine UV-visible (UVVIS) and near-infrared (NIR) channels provides
an improved evaluation of the spectral alteration. The depth of the
mafic absorption feature at 0.95 mu m is also better defined by
combining the UVVIS and NIR data. Laboratory spectra of lunar soil
samples indicate that the continuum slope derived from the 1500/750 nm
ratio is closely related to the concentration of fine-grained
submicroscopic iron (Is). The continuum slope therefore provides an
evaluation of the spectral alteration of the surface, which can be
subtracted from the 1 or 2 mu m absorption band depths to retrieve
compositional information. This method has been applied to the
Aristarchus plateau, which exhibits a broad range of mineralogical
composition and maturity. A nine-channel multispectral mosaic of 680
Clementine images of the Aristarchus plateau has been processed. Eight
telescopic spectra have been used to check the validity of the reduction
process for the near infrared bands. The 1 mu m absorption band, once
corrected for spectral alteration, provides an evaluation of the initial
FeO content in mafic silicates (mafic iron). Lunar soil samples show
that it is possible to quantitatively map mafic iron with this
technique. Our results are in good agreement with those obtained using
the algorithm of Lucey et al. {[}1995, 1998a], which is based on UVVIS
bands alone. The mafic iron content and total iron content which can be
derived from the combined UVVIS and NIR data sets are less sensitive to
local slopes than that derived from Lucey et al.'s method. This new
method could therefore be useful for investigating areas at middle to
high latitudes. Removing spectral alteration from the 2000/1500 nm ratio
also makes possible a better discrimination between olivine and pyroxene
within identified mare basalts on the Aristarchus plateau.