Photometric studies of complex surfaces, with applications to the Moon

The reflection laws of a wide variety of surfaces have been measured. The factors that govern the optical scattering characteristics of complex surfaces are discussed, and the properties of surfaces that scatter light like the moon are specified. Surfaces of solid rocks, volcanic slags, or coarsely ground rock powders do not have the intricate structure necessary for backscattering light strongly, but finely pulverized dielectric particles can build extremely complex surfaces that can reproduce the lunar scattering law. It is concluded that the surface of the moon is covered with a layer of fine rock dust composed of particles of the order of 10-micron average diameter and that 90 per cent of the volume of the surface layer is voids.