Definition of Effective Brightness Temperature Difference and its Geological Significance

Brightness temperature difference (TBD) derived from microwave radiometers (MRMs) onboard the Chang’e (CE)-1/2 satellites has been widely used to characterize basaltic flows on the lunar surface. However, the physical attributes of TBD and their geological correlations are not yet fully constrained. Based on the radiative transfer equation and the heat equation, a new TB model of the regolith is produced by considering parameters such as location, regolith composition, slope, and lunation hour. Subsequently, a TBD model is constructed from the difference in simulated TB at two different lunation hours. The simulation results show that regolith composition controls the TBD, with contributions also from latitude or surface temperature variations. To mitigate the variations with latitude or surface temperature, the TBD supplement (supTBD) model is proposed to generate the effective TBD (TBD ${}_{\mathrm {eff}}$ ) by calculating the difference in simulated TB between the target location and its equivalent value at the equator. The results show that: 1) the TBDeff effectively weakens the influence of latitude change; 2) TBDeff better distinguishes variations in subsurface deposits, particularly concerning TiO2 abundance and the mare basaltic units; and 3) in lunar highlands, TBDeff demonstrates a positive correlation between microwave propagation and rocks, presenting an inhomogeneous distribution in both lateral and vertical directions. These findings are instrumental for evaluating subsurface deposits and the evolution of impact craters on the Moon from a new perspective.