THE EFFECT OF SURFACE-ROUGHNESS ON LUNAR THERMAL EMISSION-SPECTRA

Although attempts have been made to interpret mid-infrared spectra of the Moon and other atmosphereless bodies in terms of surface composition, we show that surface roughness plays an equally important role when interpreting low to moderate resolution mid-infrared spectra of the Moon. In order to understand this influence, we model surface roughness as a distribution of paraboloidal craters parameterized by fractional coverage and depth-to-diameter ratio. This model explains, to first order, the differences in spectral radiance seen in ratios of one lunar spectrum to another which have been attributed to differences in composition by some authors. We have also developed a technique by which surface roughness can be measured with infrared colors, in such a way that the result is insensitive to compositional effects.