Calculating iron contents of lunar highland materials surrounding Tycho crater from integrated Clementine UV‐visible and near‐infrared data

Abstract

Optical properties of lunar surface materials are modified by exposure to the space environment, including bombardment by solar wind particles and micrometeorites. One of the main problems in the interpretation of lunar spectral observations is to separate the effects of exposure (“space weathering”) and those due to the composition of the soils (mainly iron and titanium content). Here we use Clementine near‐infrared (NIR) data to investigate this problem for highland‐type soils in the Tycho crater area. Our approach is based on the methods developed for an analysis of a mare region near Aristarchus Plateau [Le Mouélic et al., 2000]. We show that the systematic relationships between spectral parameters (1‐μm band depth and continuum slope), which were previously observed in a mare area with varying maturity degree, are also valid for highland‐type soils. This technique aimed at evaluating the iron content of the surface materials from Clementine UV‐visible (UVVIS) and near‐infrared data can therefore be applied globally. This approach complements the widely used method of Lucey and coworkers, which relies on the UV‐visible bands only. The proposed method relies mostly on band ratios. The iron map produced from this method is therefore less dependent on topography than the iron estimates obtained with UV‐visible data alone, where brightness is one of the controlling parameters. Therefore the proposed approach should be particularly useful at middle to high latitudes, where local topography generates large variations in brightness and therefore hampers the interpretation of iron maps produced from UV‐visible bands only.