Previous studies have reported the existence of water ice in the lunar polar regions, but estimations of water ice using different methods vary in certainty, precision, location, and abundance. Spectral analysis is one of the major ways for estimating lunar water ice abundance. However, low spatial resolution and signal-to-noise ratio are the disadvantages of hyperspectral images. In this study, the images captured by the multi-band imager (MI), characterized by higher spatial resolution and signal-to-noise ratio than hyperspectral images, onboard the Japanese Moon orbiter Selenological and Engineering Explorer (SELENE), are used to retrieve water ice in lunar polar regions. We analyzed reflectance in near-infrared bands after topographic correction to reduce the misinterpretation of the properties of the lunar surface. Through qualitative spectral analysis and quantitative water ice retrieval, the water ice abundance of sunlit areas in Shackleton Crater, de Gerlache Rims 1 and 2, Connecting Ridge, Connecting Ridge extension, and Peak Near Shackleton are obtained. The sunlit inner wall of Shackleton Crater has the highest possibility to contain water ice among the four regions, the estimated abundance ranges from 2 to 3 wt.%, which is consistent with previous studies in terms of order of magnitude. Reproducibility test suggests that the parallax effect of MI is small to ensure robust conclusions. When artificial noise was introduced, water ice abundance variations were limited to 1 wt.% in only a few areas, revealing that the results exhibit robustness against noise interference.

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.

The Diviner Lunar Radiometer Experiment on the Lunar Reconnaissance Orbiter and the Microwave Radiometer (MRM) onboard Chang'e-2 (CE-2) orbiter performed nearly coincident measurements of the lunar south polar region in 2010-2011. In this study, we reconcile infrared data from Diviner and microwave data from MRM to reveal thermal behavior of lunar regolith at very low temperatures. Assuming a uniform density structure and dielectric properties across the polar region, we retrieve a relative apparent thermal-gradient map based on radiative transfer model. The result shows apparent thermal gradients in the permanently shadowed regions (PSRs) are much larger than that in non-PSRs, which implies a systematic difference in thermal conductivity and/or density of lunar regolith in PSRs. We also model surface temperature and microwave brightness temperature over time in PSR and non-PSR locations. The modeling results at these representative locations and the thermal gradient map confirm that the regolith in the PSRs is consistent with a much lower thermal conductivity and higher porosity than non-PSRs.