Reradiation and thermal emission from illuminated craters on the lunar surface

A model of the moon consisting of a large number of millimeter-size craters distributed over the surface is proposed to account for several of the anomalous results of infrared observations. These observations have shown that the apparent temperature of the subsolar point depends on the angle of observation. In addition, the full moon exhibits an unusual amount of infrared limb brightening. Such anomalous observations are interpreted as indicating the presence of small craters. In calculating the effect of the small-scale cratering on observations of the illuminated moon, a number of physical processes are considered. A detailed calculation of the effect of radiation interchange within the crater is made. Curves are plotted of the infrared brightness of the illuminated crater as a function of the angle of the observer, taking into account the effects of reradiation, local incidence and emission angles, and shadowing. These curves are shown to be similar to those observed for the moon. By interpreting the anomalous radiation curves as the result of small craters a relative crater density of 0.5 and a depth-to-diameter ratio of approximately 0.5 are obtained for the millimeter-scale cratering and roughness on lunar surface.