Structure Of Lunar Regolith Research Articles

The Lunar Regolith Structure and Electromagnetic Properties of Chang’E-5 Landing Site

On 1 December 2020, China’s Chang’E-5 (CE-5) probe successfully landed in the northeastern Oceanus Procellarum. This work mainly presents the results of Lunar Regolith Penetrating Radar (LRPR) equipped on the CE-5 Lander. The lunar regolith structure of the landing site from the surface to 3-m depth is unveiled by LRPR, which found that abundant rock fragments are distributed in uniform lunar regolith. The imaging result proved that the drilling and sampling process was prevented by big rocks at about 100 cm depth. On the basis of the response of lunar soil to electromagnetic (EM) wave, the EM properties of the landing site estimate that the relative dielectric constant and the loss tangent are 2.520 ± 0.186 and 0.0133 ± 0.0020, respectively.

Stratification of Lunar Regolith Based on Attribute Analysis

On December 14, 2013, China’s Chang ’e-3 missions landed on the lunar surface, providing valuable information for better study of the moon. LPR (Lunar penetrating radar) is a very important and effective detection method. The lunar surface shallow radar data we obtained through the lunar exploration radar can be used to understand the geological structure of the lunar surface and the thickness of the lunar regolith. This paper analyzes the processed LPR data of “Chang’e-3” by using instantaneous attributes, and obtains the instantaneous amplitude attributes, instantaneous phase attributes, and instantaneous frequency attributes of the radar profile. According to the results of the instantaneous attribute analysis, the lunar regolith structure of the radar profile is divided, and it is found that it can be well matched with the previous research results.

Layering Structures in the Porous Material Beneath the Chang'e‐3 Landing Site

AbstractThe lunar penetrating radar (LPR) onboard the Chinese Chang'e‐3 (CE‐3) mission obtained high‐resolution profile data for the continuous ejecta deposits of the Ziwei crater. Geological background suggests that the continuous ejecta deposits contain few large boulders, and the ejecta deposits were largely originated from the pre‐impact regolith. Using the top ~50 ns of radar data, we estimate the bulk density and porosity for the ejecta deposits based on hyperbolic echo patterns in the radargram that are caused by subsurface boulders. The physical properties are close to those of typical lunar regolith. Numerous subparallel and discontinuous short layers are visible in the radargram of the continuous ejecta deposits. The dielectric coefficients of the layering structures are estimated, and their permittivity is slightly larger than that of typical lunar regolith and less than that of basaltic rocks. Cratering physics together with the geological context of this area suggest that the layering structures are most likely ground gravels and/or melt‐welded breccias that were sheared due to the horizontal momentum of the impact ejecta. This interpretation is indicative of the origin of the enigmatic layering structures in regolith core samples returned by the Apollo and Luna missions. The results also highlight the importance of ejecta emplacement in shaping the structure of lunar regolith.

Estimated Lunar Regolith Structure Based on the Least-Squares Kirchhoff Migration of CE-3 Lunar Penetrating Radar Data

The lunar penetrating radar (LPR) carried on the Chang E-3 Yutu Rover observations at 500 MHz successfully reveals the thickness and geological structure of the shallow lunar regolith. Previous work used the calculated permittivity and the migration image to estimate the layer interface and local target. In this letter, a least-squares Kirchhoff migration (LSM) algorithm is presented to reduce the migration artifacts (i.e., recording footprints) due to incomplete data. Both synthetic and CE-3 LPR data are used to test the effectiveness of the LSM method. The numerical results show that LSM can achieve a much superior image quality than Kirchhoff migration and frequency-wavenumber (F-K) migration results. Based on the LSM result of CE-3 LPR data, we can find evident strata reflection and continuous distinct layers in the shallow lunar subsurface below the CE-3 site. It provides a more reliable and robust way to interpret the lunar regolith structure.

Comparison of Dielectric Properties and Structure of Lunar Regolith at Chang'e‐3 and Chang'e‐4 Landing Sites Revealed by Ground‐Penetrating Radar

AbstractOn 3 January 2019, the Chang'e‐4 (CE‐4) touched down on the Von Karman crater located inside the South Pole‐Aitken Basin, providing for the first time the opportunity for in situ measurements of the lunar regolith at the farside of the Moon. The CE‐4 ground penetrating radar reveals that fine‐grained regolith, coarse impact ejecta, and fractured bedrocks lie beneath the exploration path of the Yutu‐2 rover. The variations of regolith permittivity with depth and the radargrams indicate that the CE‐4 site has a fine‐grained regolith layer thickness of 11.1 m, which is about 1.3–3 times higher than the in situ measurement results at the Apollo and Chang'e‐3 (CE‐3) sites except for Apollo 16, possibly due to a faster weathering rate of ejecta deposits compared with coherent basalt substrates. The penetration depth of CE‐4 is about 2.85 times (in terms of round‐way delay) deeper than CE‐3, probably due to the differences in abundances of ilmenite and rocks in the regolith.

Weak Signal Extraction from Lunar Penetrating Radar Channel 1 Data Based on Local Correlation

Knowledge of the subsurface structure not only provides useful information on lunar geology, but it also can quantify the potential lunar resources for human beings. The dual-frequency lunar penetrating radar (LPR) aboard the Yutu rover offers a Special opportunity to understand the subsurface structure to a depth of several hundreds of meters using a low-frequency channel (channel 1), as well as layer near-surface stratigraphic structure of the regolith using high-frequency observations (channel 2). The channel 1 data of the LPR has a very low signal-to-noise ratio. However, the extraction of weak signals from the data represents a problem worth exploring. In this article, we propose a weak signal extraction method in view of local correlation to analyze the LPR CH-1 data, to facilitate a study of the lunar regolith structure. First, we build a pre-processing workflow to increase the signal-to-noise ratio (SNR). Second, we apply the K-L transform to separate the horizontal signal and then use the seislet transform (ST) to reserve the continuous signal. Then, the local correlation map is calculated using the two denoising results and a time–space dependent weighting operator is constructed to suppress the noise residuals. The weak signal after noise suppression may provide a new reference for subsequent data interpretation. Finally, in combination with the regional geology and previous research, we provide some speculative interpretations of the LPR CH-1 data.

Ground experiments of Chang’e-5 lunar regolith penetrating radar

The Lunar Regolith Penetrating Radar (LRPR) is an Ultra-Wideband (UWB) array-based Ground penetrating radar (GPR) onboard the lander of Chang’e-5 (CE-5) mission. The primary scientific objectives of the LRPR are to probe the thickness and structure of lunar regolith of the landing site, and support the drilling and sampling process. In order to evaluate the performance of the LRPR, a series of ground experiments are performed using the LRPR prototype mounted on a CE-5 lander model. The performance of the LRPR is evaluated by comparing the experimental data with the simulated data. Data processing and imaging method are verified, and the interferences from the lander and other aspects are analyzed. The results of the ground experiments and simulation demonstrate that the LRPR is able to meet the design requirement of 2-m detection depth. They also indicate that the upper and lower interfaces of the stratified structure in the lunar regolith can be well distinguished by the LRPR when the dielectric constant difference is greater than 0.3, and the imaging effect of the location under the dense antennas is better than that of other positions. However, the identification capability of the LRPR to the independent blocky objects is relatively poor mainly due to the clutters caused by the lander, the sparsity of the antenna elements compared to the size of the basalt block, the limited aperture of the antenna array, and the tail of the transmitted waveform.

A Study on Lunar Regolith Quantitative Random Model and Lunar Penetrating Radar Parameter Inversion

Lunar penetrating radar (LPR) is an important way to evaluate the geological structure of the subsurface of the moon. The Chang’E-3 has utilized LPR, which is equipped on the lunar rover named Yutu, to obtain the shallow lunar regolith structure in Mare Imbrium. The previous result provides a unique opportunity to map the subsurface structure and vertical distribution of the lunar regolith with high resolution. In order to evaluate the LPR data, the study of lunar regolith media is of great significance for understanding the material composition of the lunar regolith structure. In this letter, we focus on the lunar regolith quantitative random model and parameter inversion with LPR synthetic data. First, based on the Apollo drilling core data, we build the lunar regolith quantitative random model with clipped Gaussian random field theory. It can be used to model the discrete-valued random field with a given correlation structure. Then, we combine radar wave impedance and stochastic inversion methods to carry out LPR data inversion and parameter estimation. The results mostly provide reliable information on the lunar regolith layer structure and local details with high resolution. This letter presents a further research strategy for lunar probe and deep-space detection with LPR.

Lunar regolith stratigraphy analysis based on the simulation of lunar penetrating radar signals

The thickness of lunar regolith is an important index of evaluating the quantity of lunar resources such as 3He and relative geologic ages. Lunar penetrating radar (LPR) experiment of Chang’E-3 mission provided an opportunity of in situ lunar subsurface structure measurement in the northern mare imbrium area. However, prior work on analyzing LPR data obtained quite different conclusions of lunar regolith structure mainly because of the missing of clear interface reflectors in radar image. In this paper, we utilized finite-difference time-domain (FDTD) method and three models of regolith structures with different rock density, number of layers, shapes of interfaces, and etc. to simulate the LPR signals for the interpretation of radar image. The simulation results demonstrate that the scattering signals caused by numerous buried rocks in the regolith can mask the horizontal reflectors, and the die-out of radar echo does not indicate the bottom of lunar regolith layer and data processing such as migration method could recover some of the subsurface information but also result in fake signals. Based on analysis of simulation results, we conclude that LPR results uncover the subsurface layered structure containing the rework zone with multiple ejecta blankets of small crater, the ejecta blanket of Chang’E-3 crater, and the transition zone and estimate the thickness of the detected layer is about 3.25m.

Parameters and structure of lunar regolith in Chang'E-3 landing area from lunar penetrating radar (LPR) data

Chang'E-3 (CE-3) landed in the northwest Mare Imbrium, a region that has not been explored before. Yutu rover that released by CE-3 lander carried the first lunar surface penetrating radar (LPR) for exploring lunar regolith thickness and subsurface shallow geological structures. In this paper, based on the LPR data and the Panoramic Camera (PC) data, we first calculate the lunar surface regolith parameters in CE-3 landing area including its permittivity, density, conductivity and FeO+TiO2 content. LPR data provides a higher spatial resolution and more accuracy for the lunar regolith parameters comparing to other remote sensing techniques, such as orbit radar sounder and microwave sensing or earth-based powerful radar. We also derived the regolith thickness and its weathered rate with much better accuracy in the landing area. The results indicate that the regolith growth rate is much faster than previous estimation, the regolith parameters are not uniform even in such a small study area and the thickness and growth rate of lunar regolith here are different from other areas in Mare Imbrium. We infer that the main reason should be geological deformation that caused by multiple impacts of meteorites in different sizes.

Echo simulation of lunar penetrating radar: based on a model of inhomogeneous multilayer lunar regolith structure

Lunar Penetrating Radar (LPR) based on the time domain Ultra-Wideband (UWB) technique onboard China's Chang'e-3 (CE-3) rover, has the goal of investigating the lunar subsurface structure and detecting the depth of lunar regolith. An inhomogeneous multi-layer microwave transfer inverse-model is established. The dielectric constant of the lunar regolith, the velocity of propagation, the reflection, refraction and transmission at interfaces, and the resolution are discussed. The model is further used to numerically simulate and analyze temporal variations in the echo obtained from the LPR attached on CE-3's rover, to reveal the location and structure of lunar regolith. The thickness of the lunar regolith is calculated by a comparison between the simulated radar B-scan images based on the model and the detected result taken from the CE-3 lunar mission. The potential scientific return from LPR echoes taken from the landing region is also discussed.

One Moon, many measurements 1: Radiance values

Several modern optical instruments orbited the Moon during 2008 and 2009 onboard the SELENE and Chandrayaan-1 spacecraft and provided a welcomed feast of spectroscopic data to be used for scientific analyses. The different spatial and spectral resolutions of these sensors along with diverse illumination geometry during data acquisition make each set of data unique, and each instrument contributes special value to integrated science analyses. In order to provide the maximum science benefit, we have undertaken a careful cross-validation of radiance data among these orbital instruments and also a set of systematic data acquired using Earth-based telescopes. Most radiance values at 750nm fall between 0 and 100W/(m2μmsr), but a small important fraction can be up to ×2 to ×3 that value, with the largest values occurring at the highest spatial resolution. All instruments are in agreement about overall spectral properties of lunar materials, but small systematic differences are documented between instruments. Lunar radiance values measured with remote sensors for landing sites are all not as high as that estimated from laboratory measurements of returned soil. This is largely because laboratory measurements of lunar soils cannot retain or duplicate the fine structure of lunar regolith found in the natural space environment.

Review on physical models of lunar brightness temperature

Brightness temperature is a main index to reflect the energy of microwave radiation of an object. Using lunar brightness temperature data, physical properties of lunar regolith, such as thickness, heat flow and dielectric permittivity, could be interpreted. There are two methods to study brightness temperature distribution of the moon: the first is used to measure lunar brightness temperature by radio observation or spaceborne microwave radiometers, and the second is used to simulate calculation by the physical model. On the basis of the measurements of lunar brightness temperature in the history, this study analyzed the main physical model of lunar brightness temperature, also including its theory and influence factors. The authors concluded that surface and subsurface temperatures of the moon, dielectric properties and layered structure of lunar regolith were the main factors affecting the global brightness temperature of the moon. These factors should be quantified in detail in the future research.