Lunar iron abundance determination using the 2-μm absorption band parameters

In this work we report the first employment of the 2-μm absorption band parameters to estimate FeO weight percentage (wt.%) abundances from high-resolution Near-Infrared (NIR) lunar data, as measured by the SIR-2 instrument on board Chandrayaan-1. Our method is based on the algorithm originally developed by Le Mouélic et al. (Le Mouélic, S., Langevin, Y., Erard, S., Pinet, P., Chevrel, S., Daydou, Y. [2000]. J. Geophys. Res. 105, 9445–9456) for assessing FeO wt.% in lunar surface materials analyzing Clementine UVVIS and NIR data. A small fresh-looking crater was selected as a test bench to understand the detrimental effect on spectral parameters caused by the prolonged exposure of surface materials to space weather. Using both 1-μm and 2-μm absorption band parameters we found a correlation of about 90% between iron abundances estimated by our method and actual laboratory-measured values (from Apollo and Luna data-sets). Also, Moon Mineralogy Mapper (M3) data collected at the same Coordinated Universal Time (UTC) were used to verify the SIR-2 data-set. Iron abundance estimations based on these instruments were compared with the Clementine iron abundance map produced by the algorithm developed by Lucey et al. (Lucey, P.G., Blewett, D.T., Hawke, B.R. [1998]. J. Geophys. Res. 103, 3679–3699). We selected crater Tycho as a case study for comparing our FeO wt.% estimates against published ones based on Clementine data and found them in good agreement. This study confirms that the 2-μm absorption band can be interrogated effectively to estimate the FeO wt.% content of exposed lunar surface materials through their NIR reflectance characteristics. Applications of this method would potentially be of great interest to those missions to the Moon and other planetary bodies carrying spectrometers ranging above the 0.9 μm point.