Inversion of Dielectric Properties of the Lunar Regolith Media With Temperature Profiles Using Chang'e Microwave Radiometer Observations

As ground truth to utilize the surface temperature measurements from the Diviner Lunar IR Radiometer and the subsurface thermal properties from the Apollo heat-flow probes, we create a forward model to predict brightness temperatures (Tbs) from lunar regolith media in the microwave (MW) spectrum. These models can be then directly compared with and matched to the data from the MW radiometers flown aboard the Chang'e 1 and 2 (CE-1 and CE-2) missions. Based on an MW radiative transfer model and the least-mean-square method, the effective surface reflectivity and absorption coefficient of the lunar regolith are retrieved from multichannel MW Tbs. The effective complex dielectric constant of the lunar regolith as a function of the depth at different frequency channels is derived. Meanwhile, we find that the maximum penetration depth of the MW radiation at the Apollo 15 site ranges from about 30 cm at 37.0 GHz to 230 cm at 3.0 GHz and from 30 cm at 37.0 GHz to 560 cm at 3.0 GHz in the equatorial highlands, which are much lower than the previous results that were simply derived from FeO and TiO2 abundance.