Revealing regolith substructure by Chang’E-5 LRPR with optimized cable delay calibration method

The Lunar Regolith Penetrating Radar (LRPR) onboard the Chang’E 5 lander is the first antenna-array radar deployed for the exploration of an extraterrestrial object. It is able to measure the subsurface structure of the moon at a resolution of ∼10 cm. This work presents a method for calibrating the variable cable delay of the LRPR and an imaging method based on synthesis imaging from Radio Astronomy. The cable delay calibration method effectively calibrates the cable delay shift of the LRPR with a nanosecond-level precision. To validate the accuracy of the cable delay method, we use the data obtained from both the ground experiment and the moon-exploration mission of the LRPR. The imaging method is used to visualize the subsurface structure of the Chang’E-5 (CE-5) landing site. Moreover, Finite-Difference Time-Domain (FDTD) simulation is carried out to help interpret the imaging results. The radar images derived from the LRPR observations show consistency with each other and match the bit force record during the drilling process. The results suggest that the rocks interacted with the CE-5 drill feature a size of 15 to 20 cm.