A New Method to Evaluate and Modify Chang'E-2 Microwave Radiometer Low-Frequency Data Constrained from Diviner Thermal Measurements

Microwave emission is influenced by regolith thermophysical properties that can reveal the geological evolution of the Moon. Lunar near-surface microwave emission has been systematically investigated by the microwave radiometer (MRM) onboard Chinese Chang'E-2 (CE-2) lunar satellite. However, recent work showed that global calibration issues were causing discrepancies between CE-2 observations and theoretical simulations at 3.0-and 7.8-GHz channels, which influences data interpretations and applications. In this study, we use a new method to improve thermal models by employing the bolometric brightness temperature and thermophysical property of subsurface structure derived from high quality and repeated coverage Diviner data. The derived subsurface temperatures make it possible for us to improve the accuracy of microwave brightness temperature (TB) simulation within 70°N/S latitudes. We evaluate the MRM data quantitatively by comparing the global TB between modeled values and CE-2 observations (i.e., offset values) at different local times (LTs) and latitudes. The results show that offset values of the two channels vary significantly with LT, especially near 06:00 and 18:00. However, the 7.8-GHz channel presents greater (12k in average) calibration uncertainties than the 3.0-GHz channel. In addition, the offset of both the two channels becomes complex at high latitudes but presents an obvious north-south asymmetry. Finally, we modify the MRM data according to different offsets at different LTs and latitudes. The modified global TB maps provide us a new view to characterize the lunar near-surface thermal environment, especially for low-TB spots that are related to the elevated rock abundance and crater degradation.