This letter presents experimental investigations conducted on the Matanuska Glacier in Alaska to evaluate radio frequency (RF) attenuation for through-ice communications. Software-defined radio-based transceivers employing Frequency Shift Keying (FSK) modulation were utilized for measurements on both a frozen lake and directly on the glacier at 169 MHz. Received signal levels and bit error rates were measured at 1 kbit/s with and without Forward Error Correction (FEC) codes. Additionally, a through-ice link budget analysis is presented to provide insights for future wireless communication between moon landers and cryobots exploring extraterrestrial oceans beneath ice surfaces. These findings are relevant for potential deep space missions to icy moons, such as Jupiter's moon Europa, which may harbor conditions conducive to life.

Permafrost, a major component of the cryosphere, is undergoing rapid degradation due to climate change, human activities, and other external disturbances, profoundly impacting ecosystems, hydroclimate, engineering geological stability, and infrastructure. In Northeast China, the thermal dynamics of Xing'an permafrost (XAP) are particularly complex, complicating the accurate assessment of its spatial extent. Many earlier mapping efforts, despite significant progress, fall short in accounting for some key local geo-environmental factors. Thus, this study introduces a new approach that incorporates four key driving factors-biotic, climatic, physiographic, and anthropogenic-by integrating multisource datasets and in situ observations. Four machine learning (ML) models [random forest (RF), support vector machine (SVM), logistic regression (LR), and extreme gradient boosting (XGB)] are applied to simulate permafrost distribution and probability, as well as to evaluate their performance. The results indicate that models' accuracy, ranked from highest to lowest, is as follows: RF (area under the curve (AUC) =0.88 and accuracy =0.81), XGB (0.86 and 0.77), LR (0.81 and 0.73), and SVM (0.76 and 0.66), with RF emerging as the most effective model for permafrost mapping in Northeast China. Analysis of the relationships between predictors and permafrost occurrence probability (POP) indicates that vegetation and snow cover exert nonlinear effects on permafrost, while human activities significantly reduce POP. Additionally, finer soil textures and higher soil organic matter content are positively correlated with increased POP. The modeling results, combined with field survey data, also show that permafrost is more prevalent in lowlands than in uplands, confirming the symbiotic relationship between permafrost and wetlands in Northeast China. This spatial variation is influenced by local microclimates, runoff patterns, and soil thermal properties. The primary sources of model error are uncertainties in the accuracy of multisource datasets at different scales and the reliability of observational data. Overall, ML models demonstrate great potential for mapping permafrost in Northeast China.

Circular Polarization Ratio (CPR) and bistatic angle (beta), obtained using Arecibo Observatory Planetary Radar, are the two important parameters for determining the presence of water-ice on the lunar surface. In this paper investigation on the possibility of water-ice deposits on the Erlanger crater floor, located in the Permanently Shadowed Regions (PSRs) of the lunar surface has been done using bistatic Mini-RF synthetic aperture radar (SAR) data. In order to better characterize the Erlanger crater, topographic, morphology map, temperature map, PSR map, Lunar Reconnaissance Orbiter Wide Angle Camera (WAC) image, circular polarization ratio (CPR), m-chi decomposition method and bistatic angle (beta) were utilized. We have found that the Erlanger crater and its surroundings comply with the CPR > 1 condition Spudis et al. (Geophysical Research Letter 37, 2010). In the crater floor, it was also observed that parameter beta was very high, which is not a favorable condition for the water-ice regions possible. Furthermore, observations have been obtained using the m-chi decomposition method. Based on a comprehensive analysis from the SAR parameter and m-chi decomposition, the Erlanger crater exhibits characteristics of non-icy regions. Additionally, topography, morphology, temperature, and hydrogen map-based information have been observed. The comprehensive analysis suggested that the Erlanger is a young and fresh crater. From the pixels-based analysis it has been found that the availability of the possible water-ice deposits within the crater rim is very less.

High circular polarization ratio (CPR) characteristics were found in permanently shaded regions (PSRs) near the lunar poles. High CPR was regarded as a water ice index. The compact-polarimetric (CP) miniature radio frequency (Mini-RF) radar transmits left-circularly polarized signals and receives horizontally polarized ($S_{\text {HL}}$ ) and vertically-polarized ($S_{\text {VL}}$ ) echoes from the lunar surface. Statistics of the CPR data show its relations with the relative phase ($\delta$ ) between $S_{\text {HL}} $ and $S_{\text {VL}} $ and the degree of polarization ($m$ ) but few interpretations were provided. The average CPR data reach the maximum and minimum at $\delta =\pm 90{\circ }$ , respectively. As $m$ becomes very small, the CPR approaches 1. It has been found that CPR is also affected by surface roughness and incidence angle of radar waves. The CPR is now expressed in CP mode to explain the Mini-RF observation. Full-polarimetric radar echoes and CP parameters of the lunar surface are numerically simulated using the bidirectional analytic ray-tracing method. Single-bounce and multiple-bounce scattering components are included in the simulation. Radar images of the lunar crater are simulated with the digital elevation model (DEM) data. The $H-\alpha $ decomposition derived from the full-polarimetric simulation is presented to analyze $\delta $ and $m$ . Simulated radar images with different surface roughness are analyzed statistically to study the functional dependences of $\delta $ , ${m}$ , and CPR on incidence angle and roughness. Relationships among $\delta $ , $m$ , and CPR are used to analyze the effects of incidence angle, roughness, TiO2, and rock abundance on the scattering components. The CPR, $m$ , and $\delta $ of PSR craters of different ages are compared with those of nonpolar craters. The results indicate that the CPR, $m$ , and $\delta $ are unlikely to be unambiguous evidence of water ice.