This study investigates the detectability of a putative layer of regolith containing water ice in the lunar polar regions using ground penetrating radar (GPR). Numerical simulations include realistic variations in the relative permittivity of the lunar regolith, considering both density and, for the first time, the effects of temperature on permittivity profiles. We follow the case of previous theoretical studies of water migration, which suggest that water ice accumulates at depths ranging from a few centimeters to tens of centimeters, appropriate depths to explore using GPR. In particular, frequency-modulated continuous wave (FMCW) radar is well-suited for this purpose due to its high range resolution and robust signal-to-noise ratio. This study evaluates two scenarios for the presence of lunar water ice: (1) a layer of regolith containing water ice at a depth of 5 cm, with a thickness of 5 cm, and (2) a layer of regolith containing water ice at a depth of 20 cm, with a thickness of 10 cm. Our computational results show that FMCW GPR, equipped with a dynamic range of 90 dB, is capable of detecting reflections from the interfaces of these layers, even under conditions of low water ice content and using antennas with low directivity. In addition, optimized antenna offsets improve the resolution of the upper and lower interfaces, particularly when applied to the surface of ancient crater ejecta. This study highlights the critical importance of understanding subsurface density and temperature structures for the accurate detection of water-ice-bearing regolith layers.

Biopolymers have recently been used as ecofriendly materials for soil improvement in terms of stabilization, compressibility, and engineering parameters. The objective of this study is to assess the effect of biopolymer content in sand mixtures during freeze - thaw repetitive loading cycles. The biopolymers were mixed at weight ratios of 0.0, 0.5, 1.0, 2.0, 5.0, and 10 % (BPC 0.0 - BPC 10), and the relative density and degree of saturation were fixed at 60 % and 20 %, respectively. The measurement system was located in an ice chamber for freeze - thaw, and 100 cycles of repetitive loads were applied. The test results showed that the deformation decreased from BPC 0.0, to BPC 1.0 owing to the cementation effect produced by the biopolymer chain and coating. However, the deformation increased from BPC 1.0 to BPC 5.0 because high -viscosity solutions might separate the sand particles, causing a density reduction and generating more deformation by compaction. The relative permittivity varied with respect to BPC and freeze - thaw repetitive loading stages that were affected by unfrozen water content, volume contraction, and water consumption during dehydration. The shear wave velocity gradually increased from BPC 2.0 to BPC 10 because the effect of fines in coarse - fine mixtures, rather than the cementation effect. Therefore, the module containing the sensors used in this study can be used to understand the role of biopolymers as reinforcing materials in railway subgrades.

The tau -omega model is expanded to properly simulate L -band microwave emission of the soil-snow-vegetation continuum through a closed -form solution of Maxwell's equations, considering the intervening dry snow layer as a loss -less medium. The error standard deviations of a least -squared inversion are 0.1 and 3.5 for VOD and ground permittivity, over moderately dense vegetation and a snow density ranging from 100 to 400 kg m -3 , considering noisy brightness temperatures with a standard deviation of 1 kelvin. Using the Soil Moisture Active Passive (SMAP) satellite observations, new global estimates of VOD and ground permittivity are presented over the Arctic boreal forests and permafrost areas. In the absence of dense in situ observations of ground permittivity and VOD, the retrievals are causally validated using ancillary variables including ground temperature, above -ground biomass, tree height, and net ecosystem exchange of carbon dioxide. Time -series analyses promise that the new data set can expand our understanding of the land-atmosphere interactions and exchange of carbon fluxes over Arctic landscapes.

PROSPECT is a comprehensive payload package developed by the European Space Agency which will support the extraction and analysis of lunar surface and subsurface samples as well as the acquisition of data from additional environmental sensors. The key elements of PROSPECT are the ProSEED drill and the ProSPA analytical laboratory. ProSEED will support the acquisition of cryogenic samples from depths up to 1 m and deliver them to the ProSPA instrument. ProSPA will receive and seal samples in miniaturized ovens, heat them, physically and chemically process the released volatiles, and analyze the obtained constituents via mass spectrometry using two types of spectrometers. Contextual information will be provided by cameras which will generate multi-spectral images of the drill working area and of acquired samples, and via temperature sensors and a permittivity sensor that are integrated in the drill rod. The package is designed for minimizing volatile loss from the sample between acquisition and analysis. Initially developed for a flight on the Russian Luna-27 mission, the payload package design was adapted for a more generic lander accommodation and will be flown on a lunar polar lander mission developed within the NASA Commercial Lunar Payload Services (CLPS) program. PROSPECT targets science and exploration in lunar areas that might harbor deposits of volatiles, and also supports the demonstration of In-Situ Resource Utilization (ISRU) techniques in the lunar environment. PROSPECT operations are designed to be automated to a significant degree but rely on operator monitoring during critical phases. Here, we report the PROSPECT flight design that will be built, tested, and qualified according to European space technology engineering standards before delivery to the lander provider for spacecraft integration. The package is currently in the hardware manufacturing and integration phase with a target delivery to the NASA-selected CLPS lander provider in 2025.

Frozen soil is a complex four-phase porous medium consisting of soil solid/rock, air, unfrozen/liquid water and ice at the subzero temperatures. Freeze-thaw cycles change the magnitude of total soil water content as well as the unfrozen water/ice ratio in frozen soil that affects soil structure and strength, infiltrability/permeability, water availability for microbial activity and chemical reactions, solute concentration and distribution, and thermodynamics. Accurate quantification of unfrozen water content is therefore critical to understand frozen soil hydrological, biogeochemical, thermal and mechanical properties and processes under climate change. Currently a variety of techniques and methods have been applied to obtain unfrozen water content in frozen soils. However, only few studies have attempted to review and synthesize these works. The objective of this study was therefore to review and collate currently available methods determining unfrozen water content in frozen soils. The principles, applications, advantages and limitations of these methods were reviewed and categorized into five categories: a pressure-based method, radioactive-methods, electromagnetic-methods, thermal-methods, and a sound-based method. Models for indirectly estimating unfrozen water content based on empirical temperature relationships, the soil water/moisture retention characteristic, and the vG-Clapeyron model, were also summarized. There is no direct method to estimate ice content but it can be indirectly calculated based on water balance (i.e., difference between total and unfrozen soil water content). The review is closed with a brief review of future needs and perspectives for simultaneous measurement of unfrozen water and ice contents in the laboratory and in the field.

Tree root systems are crucial for providing structural support and stability to trees. However, in urban environments, they can pose challenges due to potential conflicts with the foundations of roads and infrastructure, leading to significant damage. Therefore, there is a pressing need to investigate the subsurface tree root system architecture (RSA). Ground-penetrating radar (GPR) has emerged as a powerful tool for this purpose, offering high-resolution and nondestructive testing (NDT) capabilities. One of the primary challenges in enhancing GPR's ability to detect roots lies in accurately reconstructing the 3-D structure of complex RSAs. This challenge is exacerbated by subsurface heterogeneity and intricate interlacement of root branches, which can result in erroneous stacking of 2-D root points during 3-D reconstruction. This study introduces a novel approach using our developed wheel-based dual-polarized GPR system capable of capturing four polarimetric scattering parameters at each scan point through automated zigzag movements. A dedicated radar signal processing framework analyzes these dual-polarized signals to extract essential root parameters. These parameters are then used in an optimized slice relation clustering (OSRC) algorithm, specifically designed for improving the reconstruction of complex RSA. The efficacy of integrating root parameters derived from dual-polarized GPR signals into the OSRC algorithm is initially evaluated through simulations to assess its capability in RSA reconstruction. Subsequently, the GPR system and processing methodology are validated under real-world conditions using natural Angsana tree root systems. The findings demonstrate a promising methodology for enhancing the accurate reconstruction of intricate 3-D tree RSA structures.

The polar regions of Mars as well as the ice-covered moons such as Saturn's Enceladus and Jupiter's Europa have emerged as significant targets for ongoing and future space missions focused on investigating potentially habitable celestial bodies within our solar system. A key objective of these missions is to explore subglacial water reservoirs lying beneath the ice crusts of moons, such as Europa. The utilization of melting probes shows immense promise for achieving this goal. However, in addition to the capability to melt through the ice body, such a probe must also be able to identify the ice-water interface as well as obstacles in its path, such as cavities or meteoric rocks. To address these challenges, we present a forefield reconnaissance system (FRS) featuring a hybrid sensing approach that combines radar and sonar both integrated into the tip of a melting probe. Furthermore, the system includes an in situ permittivity sensor to ensure accurate radar range assignment and to gather scientific data about the ice body. The system has been integrated into a demonstrator melting probe and tested in a terrestrial analog scenario. Measurements at the Jungfraufirn in Switzerland confirm the potential of the developed system.

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 detection and characterization of lunar resources, including water ice, is a key area of interest for a new generation of lunar missions. The electrical properties of water ice in the extremely low frequency range support its detection by means of in-situ permittivity measurements. A new type of miniaturized subsurface permittivity sensor is presented, which is under development for the PROSPECT package on the Luna-27 lander mission. Here, the sensor concept is described, key design features are presented and possible operations modes are introduced. The expected accuracy for measurements of the relative permittivity along the borehole is similar to 10-15% and depends mainly on the accuracy of borehole geometry models. Laboratory test results from a prototype sensor on a water ice/simulant mixture at cryogenic temperatures are presented, demonstrating the capability to detect water ice at 125 K. The improved capabilities of the flight design are discussed, operational modes are explained and alternative electrode configurations for lunar landers and rovers are proposed.

Knowledge of complex permittivity of lunar soil at lunar pole temperature (-196 degrees C) plays an important role in estimating the presence of water ice in permanently shadowed regions at lunar poles using microwave remote sensing techniques. In this letter, complex permittivity [both real part (epsilon') and imaginary part (epsilon '')] of terrestrial analogue of lunar soil (TALS) has been measured at room temperature (30 degrees C) and lunar pole temperature (-196 degrees C) using liquid nitrogen (LN2) for different percentages of water content. The measurements are carried out at two microwave frequencies, namely, 2.38 GHz (S-Band, 12.6 cm wavelength) and 7.2 GHz (X-band, 4.2 cm wavelength). An increase in both real part (epsilon') and imaginary part (epsilon '') is observed with the corresponding increase in water content at both frequencies and temperatures. However, the observation states that the increase in complex permittivity is much faster for 30 degrees C than at -196 degrees C for both microwave frequencies. These results are unique because such data of complex permittivity of TALS mixed with different percentages of water at 30 degrees C and -196 degrees C, to the best of our knowledge, are not reported in the literature. The measurements would help in detecting water ice and in its quantification over the lunar surface.