A Novel Approach for Permittivity Estimation of Lunar Regolith Using the Lunar Penetrating Radar Onboard Chang’E-4 Rover

Abstract

Accurate relative permittivity is essential to the further analysis of lunar regolith. The traditional hyperbola fitting method for the relative permittivity estimation using the lunar penetrating radar generally ignored the effect of the position and geometry of antennas. This paper proposed a new approach considering the antenna mounting height and spacing in more detail. The proposed method is verified by numerical simulations of the regolith models. Hence the relative permittivity of the lunar regolith is calculated using the latest high-frequency radar image obtained by the Yutu-2 rover within the first 24 lunar days. The simulation results show that the relative permittivity is underestimated when derived by the traditional method, especially at the shallow depth. The proposed method has improved the accuracy of the estimated lunar regolith relative permittivity at a depth of 0–3 m, 3–6 m, and 6–10 m by 35%, 14%, and 9%, respectively. The thickness of the lunar regolith at the Chang’E 4 landing site is reappraised to be 11.1 m, which improved by ~8% compared with previous studies.

Dielectric Properties of Lunar Materials at the Chang’e-4 Landing Site

“…The model is 10 m in length, and 11 m in depth, and the spatial steps in the X (length) and Y (depth) direction are both 0.005 m. The time window is 150 ns, the time step is 0.0118 ns. The moving steps of both transmitter and receiver antenna are 0.05 m. The average permittivity of background material is 3.5, which is consistent with the result of Lai et al [13] and Wang et al [15]. The relative loss tangent is set as 0.02, which indicates the average conductivity of the model is about 2 × 10 −3 (e.g., Figure 3b).…”

“…Furthermore, Lai et al (2020) used the impact crater ejecta empirical model to estimate the ejecta thickness of the Finsen Crater in the Chang'e-4 landing site to be 7.9 meters, close to the thickness of the lunar regolith based on the radar observation [12]. In summary, recent research showed that there is a 12 m-thick fine regolith layer under the Yutu-2 rover's motion path, and most of surficial materials came from the Finsen Crater [13][14][15][16][17].…”

“…In radargrams, there are continuous horizontal reflectors inside the coarse-grained materials [13][14][15][16][17]. Zhang et al (2020) argued that there are 4-5 layers of impact ejecta blanket coverage between 12 and 40 meters under the motion path of the Yutu-2 rover [16].…”

Moon-Based Ground Penetrating Radar Derivation of the Helium-3 Reservoir in the Regolith at the Chang'E-3 Landing Site

“…In addition, the thickness of the regolith is unevenly distributed over the whole Moon [44]. Two high-precision in-situ radars measurement on the Moon suggest that the thickness of regolith is >10 m, e.g., Chang'E-3 and Chang'E-4 sites [26], [67], [68], [69], indicating that the global thickness of regolith is likely to be underestimated.…”

On the Limitations of Hyperbola Fitting for Estimating the Radius of Cylindrical Targets in Nondestructive Testing and Utility Detection

“…1). Although hyperbola fitting can be modified to address non-flat surfaces [18] and air-coupled antennas [19], nonetheless, the scenario mentioned above is the most typical and mainstream case study under consideration. Hyperbola fitting only utilises the shape of the hyperbola, meaning that it is amplitudeagnostic.…”