The precise detection of water-ice distributions within the permanently shadowed regions (PSRs) of the lunar south polar region is of paramount importance. We applied a polarimetric method for water-ice detection (PM4W) that utilizes Mini-RF data. The PM4W method incorporates several key radar scattering properties with topographical and environmental characteristics to detect water-ice within the lunar south polar region of 87 degrees S-90 degrees S. The method successfully identified 1578 water-ice containing pixels (each representing a 30 m x 30 m area) in the lunar shallow subsurface (1-3 m) at the south polar region, of which 1445 (similar to 91%) are spatially clustered in 29 PSRs. When comparing Mini-RF with M3 (each point representing a 280 m x 280 m area) using a buffer-based fuzzy assessment method, we found a pixel consistency of 60% and area consistency of 11%, which can be attributed to the differences in spatial resolution, positioning accuracy, and depth sensitivity. Moreover, over 90% of the water-ice pixels detected by Mini-RF are located within PSRs, accounting for 0.025% of their total area. In contrast, only 68% of the pixels detected by M3 are within PSRs, covering 0.760% of the PSRs area, which is approximately 30 times greater than the Mini-RF detections. The finer spatial resolution of the Mini-RF enables it to reveal previously undetectable features that align with the environmental mechanisms of water-ice storage. Our work contributes to assessing the potential presence of water-ice in vital exploration areas, providing pertinent indications for future lunar probes to identify water-ice on the Moon directly.

Detection of water-ice deposits using synthetic aperture radar (SAR) is a cost-effective, and efficient approach to understand lunar water resources. As water is crucial to supporting human-based space exploration, current and near upcoming lunar missions are primary concentrated on mapping and quantification of water ice exposures on surface and subsurface levels. The circular polarization ratio greater than one (CPR >1) derived using the orbital radar observations is considered as an important SAR derived parameter for water-ice detection. This study aims to investigate 14 craters near the lunar poles with high CPR (CPR >1), as identified in previous studies, using the L-band (24 cm) dual frequency synthetic aperture radar (DFSAR) onboard Chandrayaan-2. In addition to CPR, we computed the degree of polarization (DOP) after applying parallax error correction that helps in reducing misinterpretation. Our findings are based on orthorectified DFSAR calibrated data analysis. We found that the CPR of crater interiors is not significantly different from that of their surroundings, and this pattern is consistent throughout all the 14 craters selected. Further, we also found a linear inverse relationship between CPR and DOP for the interior and exteriors of the craters, with R-2 0.99, indicating a strong correlation between these two parameters. We found only 2 % of total pixels are above CPR > 1, which indicates that there is less possibility of homogeneous water-ice but the possibility of water-ice mixed with the subsurface regolith cannot be ruled out.

A remote monitoring system based on the global navigation satellite system was established at the Limin Tunnel portal of a high-speed railway to investigate the damage evolution of silty clay slopes in cold regions. Displacement, temperature, and soil moisture data were collected from four locations susceptible to instability. A discrete element model of the slope was established based on the measured data. Moreover, a coupled expansion method incorporating water-ice particle phase transition was used to analyze the microscopic damage characteristics, including surface displacement, particle interactions, and internal crack development. The results show that displacement variation is most pronounced during rapid freezing and fluctuating thawing phases, with the slope's toe experiencing more significant displacement than its crest. During rapid freezing, soil particle contact failure occurs when the bond strength between clay particles is insufficient to counteract the frost heave pressure. The development of cracks in the silty clay is rapid, with shear cracks accounting for 90.43% of the total.

The frost damage of rock mass poses a serious threat to the safety and stability of tunnels in cold regions, and the related thermo-hydro-mechanical (THM) coupling model under low-temperature conditions has been a key focus of research. This paper proposed a cryogenic THM coupled model (TOUGH-FEMM) to study the frost heave behavior of cold-region tunnels. Key issues including heat transfer, thermal stress, water-ice phase transition, unfrozen water, frost heave deformation, and ice-rock interaction are systematically addressed in the proposed model. Specifically, frost pressure in pores and cracks is derived separately to better simulate the ice expansion effect in rock masses. The proposed model is first validated against an experimental test and then applied to a practical cold-region tunnel to reveal the evolution of temperature, frost pressure and frost heave fields, as well as the tunnel stability. Moreover, the effects of cracks and frost damage on tunnel stability under freeze-thaw cycles are discussed. The work detailed herein provides an efficient tool for the THM coupled process in cold- region tunnels.

This review article provides an overview of various aspects of lunar exploration, including missions to the Moon, collection and analysis of lunar sample data in laboratories, and the processing and analysis of remote sensing data, particularly using radar techniques. Both remote sensing and in-situ methods are critical for advancing our understanding of the lunar surface and its properties. This review article focuses on the identification and quantification of water-ice deposits located in areas such as Permanently shadowed areas (PSRs) and the lunar poles ( Lunar Poles and PSRs: A Special Environment). These volatile resources have the potential to serve as valuable sources of fuel for future missions, making it crucial for the lunar community to determine their abundance and distribution. After thoroughly examining lunar samples using high-precision laboratory techniques, many preconceptions were dispelled which is highlighted in the Laboratory Investigation of Lunar samples. But as in-situ observations are difficult to acquire, especially terrestrial bodies samples, remote sensing techniques allow the global understanding of the surface. The article specifically highlights the importance of understanding the electrical characteristics of the lunar surface and how radar inversion can provide valuable information in this regard. The Conclusion of this review article serves as a key takeaway for readers, underscoring the critical role that both in-situ and remote sensing techniques play in advancing our understanding of the Moon. (c) 2023 COSPAR. Published by Elsevier B.V. All rights reserved.

The mapping of available water-ice is a crucial step in the lunar exploration missions. Ground penetrating radars have the potential to map the subsurface structure and the existence of water-ice in terms of the electromagnetic properties, specifically, the permittivity. Slight differences in permittivity can be significantly important when applied in a dry environment, such as on the Moon and Mars. The capability of detecting a small fraction of putative water-ice depends on the permittivity changes in terms of its dependent parameters, such as the frequency, the temperature, the porosity, and the chemical composition. Our work aims at mitigating false detection or overlooking of water-ce by considering their conditions that previous researches did not cover. We measured the permittivity of different lunar regolith relevant analogue samples with a fixed 40 % porosity in the ultra-high-frequency-super-high-frequency band. We used the coaxial probe method to measure anorthosite, basalt, dunite and ilmenite at 20 C-?, -20 C-? and -60 C-?, and we find that, at -60 C-?, the permittivity decreases about 6-18 % compared with the values at 20 C-?. Within this temperature range, the permittivity is quite similar to the permittivity of water-ice. We find that the conventional calculation would overestimate the permittivity in the low temperature areas, such as the permanently shadowed regions. We also find that each component in the lunar regolith has different temperature-dependent permittivity, which might be important for radar data analysis to detect lunar polar water-ice. Our results also suggest that it should be possible to estimate the water-ice content from radar measurements at different temperatures given an appropriate method.

The Lunar Volatile and Mineralogy Mapping Orbiter (VMMO) comprises a low-cost 12U Cubesat with deployable solar arrays, X-Band/UHF communications, option of electric or chemical propulsion, the Lunar Volatiles and Mineralogy Mapper (LVMM) payload, and an optional GPS receiver technology demonstrator. The LVMM facilitates three operational modes: Active mode using illumination of the lunar surface at 532nm, 1064nm and 1560nm to enable volatiles mapping during the lunar night and within Permanently Shadowed Regions (PSRs); Passive mode during the lunar day with spectral channels at 300nm, 532nm, 690nm, 1064nm and 1560nm for mapping lunar surficial ilmenite (FeTiO3); and a Communications mode for an optical data downlink demonstration at 1560nm. Previous lunar missions have detected the presence of water-ice in the lunar South Pole region. However, there is considerable uncertainty with regards to its distribution within and across the lunar surface. A number of planned future missions will further map water ice deposits, but the spatial resolution of these observations is expected to be on the order of kilometers. The LVMM using single-mode fiber lasers can improve the special resolution of the mapping to 10s of meters. VMMO has completed the Phase A study with ESA. This paper discusses the baseline LVMM payload design and its dual-use applications for both the stand-off mapping of lunar volatiles and a high-speed optical data link demonstration. In particular, the supporting fiber-laser technology readiness was advanced through ground qualification.

Dual-frequency Synthetic Aperture Radar (SAR) operating in L- and S-band frequencies is one of the primary payloads of the Chandrayaan-2 orbiter. This payload with the capability of imaging in dual frequency (L-band: 24 cm wavelength and S-band: 12 cm wavelength) with full polarimetric mode aims for unambiguous detection, characterization and quantitative estimation of water-ice in permanently shadowed regions over the lunar poles. The payload will address the ambiguities in interpreting high values of circular polarization ratio associated with water-ice observed during previous missions to the Moon through imaging in dual-frequency fully polarimetric SAR mode. Various improved system features such as wide range of resolutions and incidence angles, synchronized L-and S-band operations, radiometer mode, are built into the instrument to meet the required science objectives, adhering to stringent mission requirements of low mass, power and data rates. Major scientific objectives of dual-frequency polarimetric SAR payload are: unambiguous detection and quantitative estimation of lunar polar water-ice; estimation of lunar regolith dielectric constant and surface roughness; mapping of lunar geological/morphological features and polar crater floors at high-resolution, and regional-scale mapping of regolith thickness and distribution.

Scientific explorations have shown that the lunar water-ice exists only in the bottom of craters of lunar South and North pole, where is permanently dark and as cold as 40K This paper presents the concept of increase the temperature of water-ice by reflecting the sunlight to a certain area using polar orbit satellite formation, such that the water-ice is more detectable. The orbit of spacecraft is designed and the expected attitude is derived based on the relative motion between the spacecraft and the water-ice. The objective is to keep the reflected light from spacecraft point to the water-ice during the process so that the water-ice can be heated by solar radiation. A nonlinear adaptive controller is developed. Numerical simulations demonstrate the effectiveness of the control algorithm.

Searching for water-ice in the lunar media has been a key issue in the moon explorations. Missions of mini-SAR and mini-RF SAR made compact-pol (polarization) measurements on lunar polar permanent shadowed region (PSR). High circular polarization ratio (CPR) data and a two-layer model were applied to studying if water ice in PSR could be retrieved. However, it has been studied that high CPR is not simply due to the presence of water ice, and the Campbell model is a degenerated half-space model, which confused final inversion. In this letter, using the mini-RF data on the PSR of Hermite-A crater on the north pole, a two-layer model with the Kirchhoff and small perturbation approximations is presented. It takes account of the surface-layering topography, which makes changes of local incidence and polarimetric base rotation. Our results do not support Calla's conclusions based on the half-space model, suggesting that the inversion of mini-RF is not so straightforward in proving water-ice existence in the PSR media. It points out that the double- and high-order scattering of random volumetric scatters on the lunar surface might play a role, and high-resolution measurements and more elaborate modeling are needed for further studies.