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11 pages, 17375 KiB

Open AccessCommunication

Pre-Orientale Southwest Peak-Ring Basin: Gravity Structure, Geologic Characteristics, and Influence on Orientale Basin Ring Formation and Ejecta Emplacement

by Jinzhu Ji, James W. Head and Jianzhong Liu

Remote Sens. 2021, 13(13), 2635; https://doi.org/10.3390/rs13132635 - 05 Jul 2021

Cited by 1 | Viewed by 1892

Abstract

The Orientale impact basin is the youngest and most well-preserved of the lunar multi-ring basins. The generally well-preserved ring structures and basin facies are distinctly anomalous in the southwestern quadrant; the outer Cordillera ring extends significantly outward, the Outer and Inner Rook mountain [...] Read more.

The Orientale impact basin is the youngest and most well-preserved of the lunar multi-ring basins. The generally well-preserved ring structures and basin facies are distinctly anomalous in the southwestern quadrant; the outer Cordillera ring extends significantly outward, the Outer and Inner Rook mountain rings are more poorly developed and show anomalous characteristics, and the Montes Rook Formation varies widely from its characteristics elsewhere in the basin interior. Based on the gravity, image, and topography data, we confirmed that the southwest region of the Orientale basin represents the location of a pre-existing ~320 km rim–crest diameter peak–ring basin centered at 108.8°W, 28.4°S, and characterized by an ~170 km peak–ring diameter. We model the structure and morphology of this large pre-Orientale peak–ring basin (about one-third the diameter of Orientale) and show that its presence and negative relief had a distinctive influence on the development of the basin rings (disrupting the otherwise generally circular continuity and causing radial excursions in their locations) and the emplacement of ejecta (causing filling of the low region represented by the peak–ring basin, creating anomalous surface textures, and resulting in late stage ejecta movement in response to the pre-existing peak–ring basin topography. The location and preservation of the peak–ring basin Bouguer anomaly strongly suggest that the rim crest of the Orientale basin excavation cavity lies at or within the Outer Rook Mountain ring. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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14 pages, 17337 KiB

Open AccessArticle

Effect of Lunar Complex Illumination on In Situ Measurements Obtained Using Visible and Near-Infrared Imaging Spectrometer of Chang’E-4

by Jiafei Xu, Meizhu Wang, Honglei Lin, Rong Wang, Qi Feng and Xuesen Xu

Remote Sens. 2021, 13(12), 2359; https://doi.org/10.3390/rs13122359 - 16 Jun 2021

Cited by 6 | Viewed by 1958

Abstract

In-situ measurements of the spectral information on the lunar surface are of significance to study the geological evolution of the Moon. China’s Chang’E-4 (CE-4) Yutu-2 rover has conducted several in-situ spectral explorations on the Moon. The visible and near-infrared imaging spectrometer (VNIS) onboard [...] Read more.

In-situ measurements of the spectral information on the lunar surface are of significance to study the geological evolution of the Moon. China’s Chang’E-4 (CE-4) Yutu-2 rover has conducted several in-situ spectral explorations on the Moon. The visible and near-infrared imaging spectrometer (VNIS) onboard the rover has acquired a series of in-situ spectra of the regolith at the landing site. In general, the mineralogical research of the lunar surface relies on the accuracy of the in-situ data. However, the spectral measurements of the Yutu-2 rover may be affected by shadows and stray illumination. In this study, we analyzed 106 CE-4 VNIS spectra acquired in the first 24 lunar days of the mission and noted that six of these spectra were affected by the shadows of the rover. Therefore, a method was established to correct the effects of the rover shadow on the spectral measurements. After shadow correction, the FeO content in the affected area is corrected to 14.46 wt.%, which was similar to the result calculated in the normal regolith. Furthermore, according to the visible images, certain areas of the explored sites were noted to be unusually bright. Considering the reflectance, geometric information, and shining patterns of the multi-layer insulation (MLI), we examined the influence of the specular reflection of the MLI on the bright spot regionsd, and found that the five sets of data were likely not affected by the specular reflection of the MLI. The results indicated that the complex illumination considerably influences the in situ spectral data. This study can provide a basis to analyze the VNIS scientific data and help enhance the accuracy of interpretation of the composition at CE-4 landing sites. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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19 pages, 6790 KiB

Open AccessArticle

Estimating the Earth’s Outgoing Longwave Radiation Measured from a Moon-Based Platform

by Hanlin Ye, Huadong Guo, Guang Liu, Jinsong Ping, Lu Zhang and Yiwen Zhang

Remote Sens. 2021, 13(11), 2201; https://doi.org/10.3390/rs13112201 - 04 Jun 2021

Cited by 10 | Viewed by 2780

Abstract

Moon-based Earth observations have attracted significant attention across many large-scale phenomena. As the only natural satellite of the Earth, and having a stable lunar surface as well as a particular orbit, Moon-based Earth observations allow the Earth to be viewed as a single [...] Read more.

Moon-based Earth observations have attracted significant attention across many large-scale phenomena. As the only natural satellite of the Earth, and having a stable lunar surface as well as a particular orbit, Moon-based Earth observations allow the Earth to be viewed as a single point. Furthermore, in contrast with artificial satellites, the varied inclination of Moon-based observations can improve angular samplings of specific locations on Earth. However, the potential for estimating the global outgoing longwave radiation (OLR) from the Earth with such a platform has not yet been fully explored. To evaluate the possibility of calculating OLR using specific Earth observation geometry, we constructed a model to estimate Moon-based OLR measurements and investigated the potential of a Moon-based platform to acquire the necessary data to estimate global mean OLR. The primary method of our study is the discretization of the observational scope into various elements and the consequent integration of the OLR of all elements. Our results indicate that a Moon-based platform is suitable for global sampling related to the calculation of global mean OLR. By separating the geometric and anisotropic factors from the measurement calculations, we ensured that measured values include the effects of the Moon-based Earth observation geometry and the anisotropy of the scenes in the observational scope. Although our results indicate that higher measured values can be achieved if the platform is located near the center of the lunar disk, a maximum difference between locations of approximately 9 × 10⁻⁴ W m⁻² indicates that the effect of location is too small to remarkably improve observation performance of the platform. In conclusion, our analysis demonstrates that a Moon-based platform has the potential to provide continuous, adequate, and long-term data for estimating global mean OLR. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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24 pages, 6664 KiB

Open AccessArticle

Investigating the Retention of Solar Wind Implanted Helium-3 on the Moon from the Analysis of Multi-Wavelength Remote Sensing Data

by Shashwat Shukla, Valentyn Tolpekin, Shashi Kumar and Alfred Stein

Remote Sens. 2020, 12(20), 3350; https://doi.org/10.3390/rs12203350 - 14 Oct 2020

Cited by 12 | Viewed by 3936

Abstract

The Moon has a large potential for space exploration and mining valuable resources. In particular, ³He provides rich sources of non-radioactive fusion fuel to fulfill cislunar and Earth’s energy demands, if found economically feasible. The present study focuses on developing advanced techniques [...] Read more.

The Moon has a large potential for space exploration and mining valuable resources. In particular, ³He provides rich sources of non-radioactive fusion fuel to fulfill cislunar and Earth’s energy demands, if found economically feasible. The present study focuses on developing advanced techniques to prospect ³He resources on the Moon from multi-sensor remote sensing perspectives. It characterizes optical changes in regolith materials due to space weathering as a new retention parameter and introduces a novel machine learning inversion model for retrieving the physical properties of the regolith. Our analysis suggests that the reddening of the soil predominantly governs the retention, along with attenuated mafic band depths. Moreover, semi-variograms show that the spatial variability of ³He is aligned with the episodic weathering events at different timescales. We also observed that pyroclastic regoliths with high dielectric constant and increased surface scattering mechanisms exhibited a ³He abundant region. For ejecta cover, the retention was weakly associated with the dielectric contrast and a circular polarization ratio (CPR), mainly because of the ³He-deficient nature of the regolith. Furthermore, cross-variograms revealed inherent cyclicity attributed to the sequential process of weathering effects. Our study provides new insights into the physical nature and near-surface alterations of lunar regoliths that influence the spatial distribution and retention of solar wind implanted ³He. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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28 pages, 7028 KiB

Open AccessArticle

Thermophysical Features of the Rümker Region in Northern Oceanus Procellarum: Insights from CE-2 CELMS Data

by Zhiguo Meng, Jietao Lei, Yuqi Qian, Long Xiao, James W. Head, Shengbo Chen, Weiming Cheng, Jiancheng Shi, Jinsong Ping and Zhizhong Kang

Remote Sens. 2020, 12(19), 3272; https://doi.org/10.3390/rs12193272 - 08 Oct 2020

Cited by 11 | Viewed by 3125

Abstract

The Rümker region is located in the northern Oceanus Procellarum, which has been selected as the landing and sampling region for China’s Chang’e-5 (CE-5) mission. The thermophysical features of the mare units are studied in detail using the brightness temperature (TB) maps (TB, [...] Read more.

The Rümker region is located in the northern Oceanus Procellarum, which has been selected as the landing and sampling region for China’s Chang’e-5 (CE-5) mission. The thermophysical features of the mare units are studied in detail using the brightness temperature (TB) maps (TB, normalized TB, TB difference) derived from the CE-2 microwave radiometer data. The previously interpreted geological boundaries of the Rümker region are revisited in this study according to their TB behaviors: IR1, IR2, and IR3 Rümker plateau units are combined into one single unit (IR); and a hidden unit is found on the Mons Rümker; Mare basaltic units Im1 and Em1 are combined into Em1; and Em2 is more likely the extending of Im2. Each of the previous proposed landing sites and their scientific value are summarized and reevaluated. Based on this, four landing sites are recommended in order to maximize the scientific outcome of the CE-5 mission. We suggest that the Eratosthenian-aged Em4 and Em1 units as the top priority landing site for the CE-5 mission; the age-dating results will provide important clues concerning the thermal evolution of the Moon. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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19 pages, 7968 KiB

Open AccessArticle

Photometric Normalization of Chang’e-4 Visible and Near-Infrared Imaging Spectrometer Datasets: A Combined Study of In-Situ and Laboratory Spectral Measurements

by Xiaobin Qi, Zongcheng Ling, Jiang Zhang, Jian Chen, Haijun Cao, Changqing Liu, Le Qiao, Xiaohui Fu, Zhiping He, Rui Xu, Jianzhong Liu and Yongliao Zou

Remote Sens. 2020, 12(19), 3211; https://doi.org/10.3390/rs12193211 - 01 Oct 2020

Cited by 8 | Viewed by 3480

Abstract

Until 29 May 2020, the Visible and Near-Infrared Imaging Spectrometer (VNIS) onboard the Yutu-2 Rover of the Chang’e-4 (CE-4) has acquired 96 high-resolution surface in-situ imaging spectra. These spectra were acquired under different illumination conditions, thus photometric normalization should be conducted to correct [...] Read more.

Until 29 May 2020, the Visible and Near-Infrared Imaging Spectrometer (VNIS) onboard the Yutu-2 Rover of the Chang’e-4 (CE-4) has acquired 96 high-resolution surface in-situ imaging spectra. These spectra were acquired under different illumination conditions, thus photometric normalization should be conducted to correct the introduced albedo differences before deriving the quantitative mineralogy for accurate geologic interpretations. In this study, a Lommel–Seeliger (LS) model and Hapke radiative transfer (Hapke) model were used and empirical phase functions of the LS model were derived. The values of these derived phase functions exhibit declining trends with the increase in phase angles and the opposition effect and phase reddening effect were observed. Then, we discovered from in-situ and laboratory measurements that the shadows caused by surface roughness have significant impacts on reflectance spectra and proper corrections were introduced. The validations of different phase functions showed that the maximum discrepancy at 1500 nm of spectra corrected by the LS model was less (~3.7%) than that by the Hapke model (~7.4%). This is the first time that empirical phase functions have been derived for a wavelength from 450 to 2395 nm using in-situ visible and near-infrared spectral datasets. Generally, photometrically normalized spectra exhibit smaller spectral slopes, lower FeO contents and larger optical maturity parameter (OMAT) than spectra without correction. In addition, the band centers of the 1 and 2 μm absorption features of spectra after photometric normalization exhibit a more concentrated distribution, indicating the compositional homogeneity of soils at the CE-4 landing site. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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18 pages, 6864 KiB

Open AccessArticle

Spatio-Temporal Characteristics for Moon-Based Earth Observations

by Jing Huang, Huadong Guo, Guang Liu, Guozhuang Shen, Hanlin Ye, Yu Deng and Runbo Dong

Remote Sens. 2020, 12(17), 2848; https://doi.org/10.3390/rs12172848 - 02 Sep 2020

Cited by 13 | Viewed by 3041

Abstract

Spatio-temporal characteristics are the crucial conditions for Moon-based Earth observations. In this study, we established a Moon-based Earth observation geometric model by considering the intervisibility condition between a Moon-based platform and observed points on the Earth, which can analyze the spatio-temporal characteristics of [...] Read more.

Spatio-temporal characteristics are the crucial conditions for Moon-based Earth observations. In this study, we established a Moon-based Earth observation geometric model by considering the intervisibility condition between a Moon-based platform and observed points on the Earth, which can analyze the spatio-temporal characteristics of the observations of Earth’s hemisphere. Furthermore, a formula for the spherical cap of the Earth visibility region on the Moon is analytically derived. The results show that: (1) the observed Earth spherical cap has a diurnal period and varies with the nadir point. (2) All the annual global observation durations in different years show two lines that almost coincide with the Arctic circle and the Antarctic circle. Regions between the two lines remain stable, but the observation duration of the South pole and North pole changes every 18.6 years. (3) With the increase of the line-of-sight minimum observation elevation angle, the area of an intervisible spherical cap on the lunar surface is obviously decreased, and this cap also varies with the distance between the barycenter of the Earth and the barycenter of the Moon. In general, this study reveals the effects of the elevation angle on the spatio-temporal characteristics and additionally determines the change of area where the Earth’s hemisphere can be observed on the lunar surface; this information can provide support for the accurate calculation of Moon-based Earth hemisphere observation times. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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16 pages, 5423 KiB

Open AccessArticle

Estimation of Noise in the In Situ Hyperspectral Data Acquired by Chang’E-4 and Its Effects on Spectral Analysis of Regolith

by Honglei Lin, Yangting Lin, Yong Wei, Rui Xu, Yang Liu, Yazhou Yang, Sen Hu, Wei Yang and Zhiping He

Remote Sens. 2020, 12(10), 1603; https://doi.org/10.3390/rs12101603 - 18 May 2020

Cited by 6 | Viewed by 2969

Abstract

The Chang’E-4 (CE-4) spacecraft landed successfully on the far side of the Moon on 3 January 2019, and the rover Yutu-2 has explored the lunar surface since then. The visible and near-infrared imaging spectrometer (VNIS) onboard the rover has acquired numerous spectra, providing [...] Read more.

The Chang’E-4 (CE-4) spacecraft landed successfully on the far side of the Moon on 3 January 2019, and the rover Yutu-2 has explored the lunar surface since then. The visible and near-infrared imaging spectrometer (VNIS) onboard the rover has acquired numerous spectra, providing unprecedented insight into the composition of the lunar surface. However, the noise in these spectral data and its effects on spectral interpretation are not yet assessed. Here we analyzed repeated measurements over the same area at the lunar surface to estimate the signal–noise ratio (SNR) of the VNIS spectra. Using the results, we assessed the effects of noise on the estimation of band centers, band depths, FeO content, optical maturity (OMAT), mineral abundances, and submicroscopic metallic iron (SMFe). The data observed at solar altitudes <20° exhibit low SNR (25 dB), whereas the data acquired at 20°–35° exhibit higher SNR (35–37 dB). We found differences in band centers due to noise to be ~6.2 and up to 28.6 nm for 1 and 2 μm absorption, respectively. We also found that mineral abundances derived using the Hapke model are affected by noise, with maximum standard deviations of 6.3%, 2.4%, and 7.0% for plagioclase, pyroxene, and olivine, respectively. Our results suggest that noise has significant impacts on the CE-4 spectra, which should be considered in the spectral analysis and geologic interpretation of lunar exploration data. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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20 pages, 6615 KiB

Open AccessArticle

An Empirical Model to Estimate Abundance of Nanophase Metallic Iron (npFe⁰) in Lunar Soils

by Dawei Liu, Yuanzhi Zhang, Guangliang Zhang, Bin Liu, Xin Ren, Rui Xu and Chunlai Li

Remote Sens. 2020, 12(6), 1047; https://doi.org/10.3390/rs12061047 - 24 Mar 2020

Cited by 5 | Viewed by 3082

Abstract

Lunar soils gradually become mature when they are exposed to a space environment, and nanophase metallic iron (npFe⁰) generates within them. npFe⁰ significantly changes the optical properties of lunar soils and affects the interpretation of the remotely sensed data of [...] Read more.

Lunar soils gradually become mature when they are exposed to a space environment, and nanophase metallic iron (npFe⁰) generates within them. npFe⁰ significantly changes the optical properties of lunar soils and affects the interpretation of the remotely sensed data of the lunar surface. In this study, a correlation analysis was conducted between npFe⁰ abundance and reflectance spectra at short wavelengths for lunar soil samples in four size groups based on their spectral and compositional data, collected by the Lunar Soil Characterization Consortium (LSCC). Results show that 540 nm single scattering albedo (SSA) of lunar soils correlates well with their corresponding npFe⁰ abundance for each size group of lunar soil samples. However, it is poorly correlated with npFe⁰ abundance when all size groups were considered because of the strong interference from grain size variation of lunar soils. To minimize the effect of grain size, the correlation of npFe⁰ abundance with the spectral ratio of 540 nm/810 nm SSA of all size groups for LSCC samples was calculated and results show that a higher correlation existed between them (R² = 0.91). This ratio can serve as a simple empirical model for estimating npFe⁰ abundance in lunar soils. However, bias could be introduced to the estimation result when lunar soils possess a high content of agglutinitic glass and ilmenite. Our future work will focus on improving the model’s performance for these lunar soils. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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15 pages, 5409 KiB

Open AccessArticle

Lunar Regolith Temperature Variation in the Rümker Region Based on the Real-Time Illumination

by Zhen Zhong, Jianguo Yan and Zhiyong Xiao

Remote Sens. 2020, 12(4), 731; https://doi.org/10.3390/rs12040731 - 22 Feb 2020

Cited by 7 | Viewed by 3578

Abstract

Chang’E-5 will be China’s first sample−return mission. The proposed landing site is at the late-Eratosthenian-aged Rümker region of the lunar nearside. During this mission, a driller will be sunk into the lunar regolith to collect samples from depths up to two meters. This [...] Read more.

Chang’E-5 will be China’s first sample−return mission. The proposed landing site is at the late-Eratosthenian-aged Rümker region of the lunar nearside. During this mission, a driller will be sunk into the lunar regolith to collect samples from depths up to two meters. This mission provides an ideal opportunity to investigate the lunar regolith temperature variation, which is important to the drilling program. This study focuses on the temperature variation of lunar regolith, especially the subsurface temperature. Such temperature information is crucial to both the engineering needs of the drilling program and interpretation of future heat-flow measurements at the lunar landing site. Based on the real-time illumination, and particularly the terrain obscuration, a one-dimensional heat equation was applied to estimate the temperature variation over the whole landing region. Our results confirm that while solar illumination strongly affects the surface temperature, such effect becomes weak at increasing depths. The skin depth of diurnal temperature variations is restricted to the uppermost ~5 cm, and the temperature of regolith deeper than ~0.6 m is controlled by the interior heat flow. At such a depth, China’s future lunar exploration is adequate to measure the inner heat flow, considering the drilling depth will be close to 2 m. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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22 pages, 4684 KiB

Open AccessArticle

Reevaluating Mare Moscoviense And Its Vicinity Using Chang’e-2 Microwave Sounder Data

by Zhiguo Meng, Shengbo Chen, Yongzhi Wang, Tianxing Wang, Zhanchuan Cai, Yuanzhi Zhang, Yongchun Zheng and Shuo Hu

Remote Sens. 2020, 12(3), 535; https://doi.org/10.3390/rs12030535 - 06 Feb 2020

Cited by 21 | Viewed by 2981

Abstract

Mare Moscoviense (148°E, 27°N) is one of the few large maria on the lunar farside, with the thinnest crust and a positive gravity anomaly. In this paper, the Chang’E-2 Microwave Sounder (CELMS) data was employed to study the microwave thermal emission features of [...] Read more.

Mare Moscoviense (148°E, 27°N) is one of the few large maria on the lunar farside, with the thinnest crust and a positive gravity anomaly. In this paper, the Chang’E-2 Microwave Sounder (CELMS) data was employed to study the microwave thermal emission features of mare basalts in Moscoviense Basin. The time angle and linear interpolation method are used to generate the brightness temperature (T_B) maps at noon and night, as well as the T_B difference (dT_B) map. The obtained important results are as follows. (1) A new geologic map is generated with the T_B and dT_B maps using the maximum likelihood method, which gives a new expression about the basaltic units in Mare Moscoviense compared to the optical results; (2) the substrate temperature of Moscoviense Basin is likely warmer than what we know; (3) unit Ihtm (a Late (?) Imbrian, mid- to high-Ti, high-Fe basalt) is re-understood as two independent volcanic features with their own fissures; (4) the dT_B maps firstly indicate that the depth lunar regolith is homogeneous in the highlands surrounding Mare Moscoviense, at least in the microwave domain, and secondly that there exists a special material bringing about the low dT_B anomaly in the shallow layer of the east highlands. The results will be of great significance to better understand the basaltic volcanism of the Moon. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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21 pages, 11709 KiB

Open AccessArticle

Geometric Quality Assessment of Chang’E-2 Global DEM Product

by Xin Xin, Bin Liu, Kaichang Di, Zongyu Yue and Sheng Gou

Remote Sens. 2020, 12(3), 526; https://doi.org/10.3390/rs12030526 - 06 Feb 2020

Cited by 8 | Viewed by 3038

Abstract

The Chang’E-2 digital elevation model (DEM, named CE2TMap2015), which is the highest resolution DEM product in China, was released with global coverage of the lunar surface. A detailed geometric quality assessment of the product is desirable for wider applications by users. A novel [...] Read more.

The Chang’E-2 digital elevation model (DEM, named CE2TMap2015), which is the highest resolution DEM product in China, was released with global coverage of the lunar surface. A detailed geometric quality assessment of the product is desirable for wider applications by users. A novel procedure for evaluating DEM geometric quality, which investigates both the global geometric uncertainty and local gross errors, is proposed in this paper. First, the DEM was divided into regular blocks and matched with the reference DEM. Then, the characteristics of errors were investigated using the statistical information of the matched tie points. Next, the local outlier factor (LOF) algorithm was performed to locate the gross errors. In our experiment, CE2TMap2015 was evaluated using the proposed method, with SLDEM2015 as the reference DEM. The results show that there were widespread geometric inconsistencies with an area-weighted average of 183.1 m horizontally (with the standard deviation being 101.2 m) and 2.3 m vertically (with the standard deviation being 15.4 m). Gross errors were detected automatically and were excluded in the statistical analysis. The periodic errors were extracted in the frequency domain using a Fourier transform. Our research results provide instructional information for the utilization of CE2TMap2015 by world-wide users. The proposed method can be used in the assessment of other planetary DEMs. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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20 pages, 5686 KiB

Open AccessArticle

Simulation Study of Moon-Based InSAR Observation for Solid Earth Tides

by Kai Wu, Ce Ji, Lei Luo and Xinyuan Wang

Remote Sens. 2020, 12(1), 123; https://doi.org/10.3390/rs12010123 - 01 Jan 2020

Cited by 13 | Viewed by 3563

Abstract

The observation of solid earth tides (SET) provides an important basis for understanding the structure of the earth’s interior, and has long been the focus of research in geoscience. However, actually, there still exist some limitations in capturing its global-scale information only with [...] Read more.

The observation of solid earth tides (SET) provides an important basis for understanding the structure of the earth’s interior, and has long been the focus of research in geoscience. However, actually, there still exist some limitations in capturing its global-scale information only with ground stations. Remote sensing technology can realize large-scale deformation monitoring of high point density constantly. However, it is still difficult for the artificial satellite system to meet the requirements of SET monitoring in terms of field of view and temporal resolution now. In this work, the moon is hypothesized as a new platform for SET observation combined with interferometric synthetic aperture radar (InSAR) technology. Based on the tidal model and lunar ephemeris, the spatial and temporal characteristics of the SET from the lunar view were analyzed. Furthermore, the calculations demonstrate that more abundant SET information can be observed in this view. After comparing various observation modes, the single-station with repeat-pass differential InSAR was selected for this simulation. We mainly considered the restriction of observation geometry on moon-based InSAR under three signal bandwidths, thereby providing a reference for the sensor design. The results demonstrate that the moon-based platform offers the potential to become an optimal SET observation method. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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30 pages, 13419 KiB

Open AccessArticle

A Machine Learning Approach to Crater Classification from Topographic Data

by Qiangyi Liu, Weiming Cheng, Guangjian Yan, Yunliang Zhao and Jianzhong Liu

Remote Sens. 2019, 11(21), 2594; https://doi.org/10.3390/rs11212594 - 05 Nov 2019

Cited by 6 | Viewed by 4028

Abstract

Craters contain important information on geological history and have been widely used for dating absolute age and reconstructing impact history. The impact process results in a lot of ejected fragments and these fragments may form secondary craters. Studies on distinguishing primary craters from [...] Read more.

Craters contain important information on geological history and have been widely used for dating absolute age and reconstructing impact history. The impact process results in a lot of ejected fragments and these fragments may form secondary craters. Studies on distinguishing primary craters from secondary craters are helpful in improving the accuracy of crater dating. However, previous studies about distinguishing primary craters from secondary craters were either conducted by manual identification or used approaches mainly concerning crater spatial distribution, which are time-consuming or have low accuracy. This paper presents a machine learning approach to distinguish primary craters from secondary craters. First, samples used for training and testing were identified and unified. The whole dataset contained 1032 primary craters and 4041 secondary craters. Then, considering the differences between primary and secondary craters, features mainly related to crater shape, depth, and density were calculated. Finally, a random forest classifier was trained and tested. This approach showed a favorable performance. The accuracy and F1-score for fivefold cross-validation were 0.939 and 0.839, respectively. The proposed machine learning approach enables an automated method of distinguishing primary craters from secondary craters, which results in better performance. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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18 pages, 32035 KiB

Open AccessTechnical Note

Self-Organization Characteristics of Lunar Regolith Inferred by Yutu-2 Lunar Penetrating Radar

by Xiang Zhang, Wenmin Lv, Lei Zhang, Jinhai Zhang, Yangting Lin and Zhenxing Yao

Remote Sens. 2021, 13(15), 3017; https://doi.org/10.3390/rs13153017 - 01 Aug 2021

Cited by 5 | Viewed by 2223

Abstract

Most previous studies tend to simplify the lunar regolith as a homogeneous medium. However, the lunar regolith is not completely homogeneous, because there are weak reflections from the lunar regolith layer. In this study, we examined the weak heterogeneity of the lunar regolith [...] Read more.

Most previous studies tend to simplify the lunar regolith as a homogeneous medium. However, the lunar regolith is not completely homogeneous, because there are weak reflections from the lunar regolith layer. In this study, we examined the weak heterogeneity of the lunar regolith layer using a self-organization model by matching the reflection pattern of both the lunar regolith layer and the top of the ejecta layer. After a series of numerical experiments, synthetic results show great consistency with the observed Chang’E-4 lunar penetrating radar data and provide some constraints on the range of controlling parameters of the exponential self-organization model. The root mean square permittivity perturbation is estimated to be about 3% and the correlation distance is about 5–10 cm. Additionally, the upper layer of ejecta has about 1–2 rocks per square meter, and the rock diameter is about 20–30 cm. These parameters are helpful for further study of structural characteristics and the evolution process of the lunar regolith. The relatively small correlation distance and root mean square perturbation in the regolith indicate that the regolith is mature. The weak reflections within the regolith are more likely to be due to structural changes rather than material composition changes. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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18 pages, 12494 KiB

Open AccessTechnical Note

Application of Denoising CNN for Noise Suppression and Weak Signal Extraction of Lunar Penetrating Radar Data

by Haoqiu Zhou, Xuan Feng, Zejun Dong, Cai Liu and Wenjing Liang

Remote Sens. 2021, 13(4), 779; https://doi.org/10.3390/rs13040779 - 20 Feb 2021

Cited by 19 | Viewed by 2455

Abstract

As one of the main payloads mounted on the Yutu-2 rover of Chang’E-4 probe, lunar penetrating radar (LPR) aims to map the subsurface structure in the Von Kármán crater. The field LPR data are generally masked by clutters and noises of large quantities. [...] Read more.

As one of the main payloads mounted on the Yutu-2 rover of Chang’E-4 probe, lunar penetrating radar (LPR) aims to map the subsurface structure in the Von Kármán crater. The field LPR data are generally masked by clutters and noises of large quantities. To solve the noise interference, dozens of filtering methods have been applied to LPR data. However, these methods have their limitations, so noise suppression is still a tough issue worth studying. In this article, the denoising convolutional neural network (CNN) framework is applied to the noise suppression and weak signal extraction of 500 MHz LPR data. The results verify that the low-frequency clutters embedded in the LPR data mainly came from the instrument system of the Yutu rover. Besides, compared with the classic band-pass filter and the mean filter, the CNN filter has better performance when dealing with noise interference and weak signal extraction; compared with Kirchhoff migration, it can provide original high-quality radargram with diffraction information. Based on the high-quality radargram provided by the CNN filter, the subsurface sandwich structure is revealed and the weak signals from three sub-layers within the paleo-regolith are extracted. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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14 pages, 6051 KiB

Open AccessTechnical Note

Rock Location and Property Analysis of Lunar Regolith at Chang’E-4 Landing Site Based on Local Correlation and Semblance Analysis

by Hanjie Song, Chao Li, Jinhai Zhang, Xing Wu, Yang Liu and Yongliao Zou

Remote Sens. 2021, 13(1), 48; https://doi.org/10.3390/rs13010048 - 24 Dec 2020

Cited by 9 | Viewed by 2694

Abstract

The Lunar Penetrating Radar (LPR) onboard the Yutu-2 rover from China’s Chang’E-4 (CE-4) mission is used to probe the subsurface structure and the near-surface stratigraphic structure of the lunar regolith on the farside of the Moon. Structural analysis of regolith could provide abundant [...] Read more.

The Lunar Penetrating Radar (LPR) onboard the Yutu-2 rover from China’s Chang’E-4 (CE-4) mission is used to probe the subsurface structure and the near-surface stratigraphic structure of the lunar regolith on the farside of the Moon. Structural analysis of regolith could provide abundant information on the formation and evolution of the Moon, in which the rock location and property analysis are the key procedures during the interpretation of LPR data. The subsurface velocity of electromagnetic waves is a vital parameter for stratigraphic division, rock location estimates, and calculating the rock properties in the interpretation of LPR data. In this paper, we propose a procedure that combines the regolith rock extraction technique based on local correlation between the two sets of LPR high-frequency channel data and the common offset semblance analysis to determine the velocity from LPR diffraction hyperbola. We consider the heterogeneity of the regolith and derive the relative permittivity distribution based on the rock extraction and semblance analysis. The numerical simulation results show that the procedure is able to obtain the high-precision position and properties of the rock. Furthermore, we apply this procedure to CE-4 LPR data and obtain preferable estimations of the rock locations and the properties of the lunar subsurface regolith. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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12 pages, 3299 KiB

Open AccessTechnical Note

Analyzing the Magnesium (Mg) Number of Olivine on the Lunar Surface and Its Geological Significance

by Chao Zhou, Yuanzhi Zhang, Shengbo Chen and Bingxue Zhu

Remote Sens. 2019, 11(13), 1544; https://doi.org/10.3390/rs11131544 - 28 Jun 2019

Cited by 1 | Viewed by 3589

Abstract

Olivine formation is directly related to Mg/Fe content. It is also significant in estimating the geological evolution of the moon. In this study, an estimation model of relative Mg number (Fo#) for lunar olivine was presented through multiple linear regression statistics. Sinus Iridum, [...] Read more.

Olivine formation is directly related to Mg/Fe content. It is also significant in estimating the geological evolution of the moon. In this study, an estimation model of relative Mg number (Fo#) for lunar olivine was presented through multiple linear regression statistics. Sinus Iridum, the Copernicus Crater, and the pyroclastic deposit in the volcanic vents in the southeast of Orientale Basin were selected as the study areas. Olivine distribution was surveyed, and the relative Fo# calculation of olivine was implemented based on Moon Mineralogy Mapper (M³) data. Results demonstrated that olivine in the crater wall of Sinus Iridum and the Copernicus Crater had relatively high Fo#, which reflected the primitive melt. However, the difference in olivine spectral features between Sinus Iridum and the Copernicus Crater indicated different crystallization modes. The olivine in the pyroclastic deposit in the volcanic vents in the southwest of Orientale Basin also presented high Fo#, which indicated that the olivine was formed via rapid cooling crystallization and was accompanied by volcanic glass substances. As a result, the olivine relative Fo# calculated from the estimation model exhibited an important constraint implication for explanation of its causes. Full article

(This article belongs to the Special Issue Lunar Remote Sensing and Applications)

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