Lunar spectral types

The spectral reflectance properties (0.3–1.1 μ) of a number of lunar mare, upland, and bright crater areas were observed with the use of ground-based telescopes. These new data are discussed in view of earlier studies in an attempt to provide a basis for more detailed interpretation. The spectral reflectivity curves (0.3–1.1 μ) for all lunar areas studied consist of a positive sloping continuum with a superimposed symmetric absorption band centered at 0.95 μ. Upland, mare, and bright crater materials can be identified by their spectral curves. The curves for upland and mare regions show a range of shapes from fresh, bright craters to progressively darker background material that correlates with the apparent age of the surface features. The observed upland material has uniform spectral properties, but the mare material shows some variety, probably due to Ti3+ dispersed in lunar-soil glass. Copernicus and Aristarchus appear to have exposed upland material from beneath the mare but Kepler has not. This observation suggests that the mare is no deeper than about 15 km in the Copernicus area and about 6 km deep in the Aristarchus area, but in the Kepler area the mare must be at least about 5 km deep.