New Constraints on Thermal and Dielectric Properties of Lunar Regolith from LRO Diviner and CE-2 Microwave Radiometer

We derive a new constraint on the thermal and dielectric properties of the lunar regolith layer by reconciling data from the Lunar Reconnaissance Orbiter (LRO) Diviner infrared radiometer and Chang'E-2 (CE-2) microwave radiometer (MRM). The bolometric Bond albedo of the lunar surface, which characterizes the ability of the lunar surface to reflect visible radiation, is a function of incidence angle. We determined the Bond albedo by using the Lunar Orbiter Laser Altimeter 1,064-nm normal albedo and the surface temperature at noon as a function of latitude. The results suggest a modification to existing regolith thermal conductivity models based on a fit to the diurnal variation of Diviner data. Based on the thermal model, a 1-D radiative transfer and dielectric properties model is developed to fit MRM data for the global Moon. With a new dielectric loss tangent equation for highland regolith applied, our model matches MRM data well at 19.35 and 37 GHz, which are generally accepted to be well calibrated. A global map of loss tangent of the Moon at these frequencies is also obtained by fitting the diurnal amplitude of microwave brightness temperature (TB) of each location on the Moon. We find that the loss tangent of highlands regolith has a slight frequency dependence and is larger than previous studies. We also identify a large discrepancy between our theoretical model and TB obtained by CE-2 MRM at low frequencies, which is attributed to issues caused by contamination on calibration horn.