Application of remote spectral reflectance measurements to lunar geology classification and determination of titanium content of lunar soils

Plots of reflectance slope between 0.402 and 0.564 μm versus the intensity ratio between 0.564 and 0.948 μm are used to quantitatively define the mare, mare crater, upland, and bright upland crater spectral types previously presented by McCord et al. (1972a). An additional spectral type, dark mantling material, has also been found. Quantification of lunar spectral types allows direct comparison of the spectral units with geologic units established by the U.S. Geological Survey, including the dark mantling material unit. Unit age-color relationships are observed in the upland and mare crater spectral types. However, explicit correlation in the maria between stratigraphy and color measurements is not apparent. An empirical relationship is derived relating TiO2 content of the bulk lunar soils to the slope of the spectral curve between 0.402 and 0.564 μm. The relationship is noted in both laboratory and telescopic measurements and is governed by optical absorption in the glassy material of the soils. Hence the slope of the spectral curves (0.402–0.564 μm) may be useful as a new basis for establishing mappable geologic units on the moon. Examples are presented for the mare regions.