Directional characteristics of infrared emission from the moon

Infrared surveys of the illuminated Moon have shown that the lunar surface does not radiate like a Lambert emitter. A detailed description is presented of directional emission from the equatorial region of the Moon, based on brightness temperature measurements by Saari and Shorthill (1967a, b). In general, the measurements indicate that the illuminated lunar surface is anomalously warm (cool) when the Sun is behind (in front of) the observer. It is plausible to attribute such directional effects to negative surface relief. A thermal model of a cratered lunar soil is developed to examine these effects both qualitatively and quantitatively. The results of the study indicate that centimeter-and meter-scale craters, with a variety of forms, both sharp and subdued, can account for measured directional emission characteristics over a wide range of Sun and observer angles.