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 compositi on, we show that surface roughness plays an equally important role whe n interpreting low to moderate resolution mid-infrared spectra of the Moon. In order to understand this influence, we model surface roughnes s as a distribution of paraboloidal craters parameterized by fractiona l coverage and depth-to-diameter ratio. This model explains, to first order, the differences in spectral radiance seen in ratios of one luna r spectrum to another which have been attributed to differences in com position 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.