Exploring the Lunar Regolith's Thickness and Dielectric Properties Using Band-Limited Impedance at Chang'E-4 Landing Site

The Yutu-2 rover onboard China's Chang'E-4 was the first to land in the Von Karman crater on the lunar farside, where structural and dielectric properties may provide previously unknown clues to lunar formation and evolution. Based on the Lunar Penetrating Radar (LPR) with 500 MHz onboard the Yutu-2 rover, we proposed a band-limited impedance (BLIMP) inversion method to generate continuous dielectric 2-D profiles with the help of dielectric constants retrieved from point reflectors (e.g., buried rocks), which provide low-frequency information that may be lost or distorted in the LPR data pre-processing. The dielectric constants retrieved from point reflectors were transformed from dielectric constant fitting curves, where these discrete dielectric constants were calculated using the hyperbolic fitting method. We estimated that the top fine-grained regolith thickness along the rover path varies from similar to 5.3 to similar to 15.0 m in the first 27 lunar days of operation. The thickness variation could most likely be attributed to changes in ancient surface topography buried underground and ejecta from nearby craters. Compared to methods based on a singular dielectric constant, the estimated 2-D dielectric profile in this study can reduce the uncertainties in lunar regolith thickness estimation, especially in the shallow layers. The BLIMP method and the estimated regolith thickness can improve our understanding of lunar subsurface structure and formation.