Limited-interval definitions of the photometric functions of lunar crater walls by photography from orbiting Apollo

By the use of only relative photometry (intraframe) it is shown that the photometric functions of material reposed on the inner walls of some of the ypunger lunar craters photographed on the far side of the Moon from the Apollo 11 Command Module are not of a form which can be reduced to a dependence on phase angle and brightness-longitude (g, α) alone. Some other dependence on the completely general degrees of freedom described by phase angle, angle of incidence, and angle of emergence (g, i, ϵ) seems to be required. In addition, however, it has been found that a dependence of g and α is more closely approached for the crater, in the group observed, which is obviously the oldest by virtue of the roundedness of the rim crest and the mass-wasting which has occured on its inner walls. The possibility thus arises of crater age-dating by making a brightness ratio measurement together with some image geometry measurements. It is at least evident that more than one type of geologic material has been encountered.