LUNAR THERMAL EMISSION AND REMOTE DETERMINATION OF SURFACE-PROPERTIES

Grain size, bull; density (or porosity), thermal conductivity, and roc k abundance all play an important role in the thermal behavior of the lunar surface. Direct investigation of these properties of the lunar s urface layer is not presently possible, with the exception of the samp les returned from the Apollo landing sites. An indirect measurement of lunar surface properties may be possible using remote thermal infrare d observations. In order to better understand the interplay between th ese properties, a diurnal thermal model for the lunar surface and near subsurface with temperature-dependent specific heat and thermal condu ctivity was developed. The inclusion of the temperature dependence of thermal conductivity and specific heat was found to be essential when attempting to derive regolith properties of the Moon due to the large difference in surface temperatures between day and night. Although par ticle size, bulk density, and thermal conductivity cannot he investiga ted completely independently, a clear relationship between these param eters, and their effects on lunar surface temperatures, is determined. An increase in the bulk density of the regolith is found to correspon d to an increase in the nighttime temperature of the surface. Similarl y an increase in the rock fraction also raises the predicted nighttime temperatures. Increasing grain sizes correspond to decreasing nightti me temperatures. No unique set of surface properties can be determined from thermal remote sensing measurements alone. Grain size is the mos t difficult regolith property to determine remotely, and. rod; abundan ce is by far the strongest contributor to the derived thermal inertia of the bulk surface.