Earth-based radar (EBR) is an important type of remote-sensing instrument for planetary observation. EBR takes advantages in large-scale imaging swath, high repeatability, great flexibility,etc. The upcoming 233 MHz-frequency European Incoherent Scatter Scientific Association (EISCAT) 3D radar system will provide important features to lunar observation as introduced in this study. EISCAT_3D (E3D) radar is a powerful multi-static radar system. The 1.3 m-wavelength wave of E3D can penetrate deeper, about 30 m below lunar average surface which can reach the second layer, i.e. layer of ejecta. E3D radar supports dual/quadrature polarimetry, which gives it good flexibility and lower ambiguity in the inference of scatter’s properties. Also, there is less ambiguity in scattering regimes between icy and non-icy scatters for 1.3 m wavelength than for shorter wavelengths as given from the simulation results. Besides, the high topographic resolution (which requires forming interferometric baselines with distant telescope antennas) of E3D radar along with its penetration depth makes it possible for detection of sublunarean cavities by signatures of depression. As a whole, the 1.3 m-wavelength three-dimension (3-D) polarimetric imaging of the Moon by E3D radar, on a spatial resolution of about 200 m, will be valuable for obtaining new information about the geology and subsurface structure of the Moon, and can be used in search of buried water ice and sublunarean cavity,etc. Furthermore, we envision the collaboration of E3D radar with large telescope antennas in China, including Daocheng Solar Radio Telescope (DSRT) and Mingantu spectral radioheliograph (MUSER) for better imaging ability and detectivity.

The lunar surface presents an exceptionally harsh environment, while shallow subsurface cavities offer critical protection against harmful radiation, extreme thermal fluctuations, and meteorite impacts. This study integrates Diviner temperature data, LOLA albedo data, and radar-derived density profiles to perform thermal simulations of the subsurface cavity detected by ground-penetrating radar within five meters beneath the lunar near-side surface at the Chang’E-3 landing site. The primary objective is to assess its feasibility and thermal stability as a natural shelter for lunar base site selection. This paper employs the finite element method to simulate diurnal temperature variations in both intact cavities and excavated cavities with varying opening diameters. The results show that temperature fluctuations within the cavity decrease as the skylight diameter narrows. The internal thermal environment demonstrates relatively high stability, attributable to the cavity’s location in a mid-latitude region with limited solar radiation exposure and to the excellent thermal insulation properties of lunar regolith. Even in cavities with a 2-meter skylight diameter, the internal diurnal temperature variation remains within 20 K. These findings confirm the thermal feasibility of utilizing such cavities in the Chang’E-3 landing area as natural shelters for human habitation and provide valuable insights and recommendations for future lunar base siting.

The radar equipment carried by the Chang’E-3 (CE-3) mission marked the first deployment of rover-mounted ground-penetrating radar (GPR) to observe the lunar surface. This provided an unparalleled opportunity for a high-resolution investigation into the fine structure of the lunar regolith. This paper has revealed the presence of multiple discrete layers within the top 4 meters of the lunar regolith using high-frequency radar data from the CE-3 Yutu rover. Subsequently, we have established realistic models of the lunar regolith to obtain the radar simulation calculated by Finite-difference time-domain (FDTD) technology. Thus, we compare the simulated radar data with actual observational data to comprehensively confirm the existence of multiple discrete layers within the lunar regolith. Taking into consideration the geological context of the CE-3 landing site and the principles of impact crater formation, we infer that the origin of the multiple discrete layers within the top 4 meters of the CE-3 landing site is likely the by-product of multiple depositions of ejecta from nearby small craters. Our findings suggest the possibility of the widespread existence of multiple discrete layers within the lunar regolith and emphasize the significant contribution of ejecta from small impact craters to the accumulation of local lunar regolith thickness on the Moon’s surface.

This article deals with the investigation of the Martian subsurface in the Utopia Planitia region using Zhurong’s ground-penetrating radar. The low-frequency data recorded along the overall path followed by the rover are processed thanks to a customized signal processing pipeline aiming on one side to minimize the artifacts in the radargrams and, on the other one, to obtain images of the subsoil that aid the following analysis and interpretation stage. The images reveal a three-layer structure beneath the landing area up to the depth of ~40 m. The general scattering characteristics indicate the presence of$5~\sim ~8$-m regolith,$2~\sim ~3$-m fine materials, and$15~\sim ~30$m embedded with blocks generating a significant electromagnetic scattering. The existence of an upward decrease in grain size is resulted from long-term weathering and repeated impacts or the occurrence of flood events. The radargrams depict a distinctive local enhancement of the scattering at the end of the rover route from Sol 292 to Sol 325. Analysis of the layout of barchan dunes and the distribution of craters suggests that the resurfacing activity is the result of a complex combination of tectonic activities and impact events.

The Moon-based ground penetrating radar (GPR) onboard the Chang’E-4 (CE-4) Yutu-2 rover has deployed on the far side of the Moon, which provides the Moon’s far side, providing an unprecedented opportunity to study the shallow surface geological process and the history of the volcanic eruption of the Moon. The high-frequency radar observed a buried lens structure ~27 m below the lunar surface, which was interpreted as paleo-regolith by previous studies. In this study, we conducted a quantitative analysis of the dielectric properties of the buried lens structure observed during the CE-4 mission. Our results reveal that the relative permittivity and loss tangent are of the structure is ~10.5 and ~0.037, respectively. Comparing our estimated dielectric properties with those of Apollo samples and radar-observed lava flows shows that the buried lens is neither regolith nor ejecta material but possibly basalt flow. Additionally, we speculate that the buried basalt flow may represent the latest volcanic eruption on the Moon, possibly from the Eratosthenian-aged volcano that occurred approximately 2.5-2.2 billion years ago. Finally, we update the interpretation of the regolith stratigraphic structure observed by the Yutu-2 high-frequency radar at the CE-4 landing site.

This work presents the results of the Lunar Regolith Penetrating Radar (LRPR), installed at the bottom of the Chang’E-5 (CE-5) lander, which is the first antenna-array radar deployed for the investigation of an extraterrestrial body. Radar imaging results unveiled a hyperfine structure for the top 2.5-m-thick lunar regolith with an unprecedented high resolution of 5 cm. The interpretation of the results permitted to state that subsurface regolith is dominated by fine grains with abundant rock fragments. The radar imaging results were also used to drive the drilling process until a fragment jammed the core inlet at about 100-cm underground. Laboratory measurements of the samples returned at Earth allow to estimate the real part of relative permittivity and the loss tangent, which are 3.04 ± 0.02 and 0.014 ± 0.002, respectively.

Buried craters within tens of meters of lunar regolith are rarely studied but are significant for understanding the evolution of surface processes on the Moon. Here, we first report the evidence of an intact buried crater within the layered strata at Chang’E-4 (CE-4) landing site revealed by the lunar penetrating radar (LPR). The time–frequency comparative analysis method based on the variational mode decomposition (VMD) and the rock quantitative analysis method based on the local unit correlation (LUC) are proposed and applied to the processing and analysis of LPR data within 15 lunar days. The results presented by the two methods provide evidence of a buried crater at the CE-4 landing site and simultaneously reveal the rock-concentrated structure within the buried crater. According to the results, it is considered that the filling materials within the buried crater have survived the impaction and gardening during the formation of the overlying fine-grained regolith. Recent works have proposed that the near-surface material at the CE-4 landing site is mainly the lunar mantle materials excavated from the nearby Finsen crater. Therefore, the buried crater probably preserves the initial lunar mantle materials.

Chang'e-3 (CE-3) has been the first spacecraft to soft land on the moon since the Soviet Union's Luna 24 in 1976. The spacecraft arrived at Mare Imbrium on December 14, 2013, and the same day, Yutu lunar rover separated from lander to start its exploration of the surface and the subsurface around the landing site. The rover was equipped, among other instruments, with two lunar penetrating radar systems having a working frequency of 60 and 500 MHz. The radars acquired data for about two weeks while the rover was slowly moving along a path of about 114 m. At navigation point N0209, the rover got stacked into the lunar soil and after that only data at a fixed position could be collected. The low-frequency radar data have been analyzed by different authors and published in two different papers, which reported totally controversial interpretations of the radar cross sections. This paper is devoted to resolve such controversy by carefully analyzing and comparing the data collected on the moon by Yutu rover and on earth by a prototype of LPR mounted onboard a model of the CE-3 lunar rover. Such analysis demonstrates that the deep radar features previously ascribed to the lunar shallow stratigraphy are not real reflectors, rather they are signal artifacts probably generated by the system and its electromagnetic interaction with the metallic rover.