Spectral characteristics of Apollo landing sites in the VIS to NIR wavelength range

Abstract

Observations in the visible and near-infrared wavelength range have been used to characterize the spectral behaviour of the lunar nearside. Special emphasis was given to the investigation of the Apollo landing sites which give the possibility to compare remotely sensed data and spectral analyzing techniques with the compositional ground-truth provided by the lunar sample record. Two independent obervational data sets were used for this study with (1) earth-based multispectral CCD measurements in 12 colors obtained at the Mauna Kea observatory and (2) Galileo SSI images in six colors obtained during the second Earth-Moon encounter. Both data sets cover the same spectral range from 0.4 to 1.0 muem and have a comparable spatial resolution of <&#61 2 km/pixel. The analysis of the lunar soil samples shows a strong correlation between the concentrations of the main chemical constituents and spectral variations as measured in thelaboratory. In order to apply this spectral-chemical correlation to the remotely sensed data of the lunar surface, seperate correlation models were developed for each remote instrument, respectively, by folding the optical properties of the cameras with the laboratory spectra of the samples. The reliability of the modelswere tested for the observational multispectral data of the Apollo landing sites. The main chemical constituents like Fe, Ti, Ca and Al could be determined to an accuracy of a few percent and confirm the applicability of the analyzing technique to the remotely sensed data sets. Hence, the spectral-chemical correlation models allow to map the distribution of these elements in the lunar soil and to define geological surface units in terms of their composition.