Experimental results of permittivity of lunar simulated materials in the UHF-SHF band for radar explorations

Abstract 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-ice by considering their conditions that previous researches did not cover. We measured the permittivity of different lunar regolith relevant 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. We find that, at – 60 °C, the permittivity decreases about 7 – 20 \% compared with the values at 20 °C, and that permittivity changes caused by ilmenite content could lead to false detection of lunar water-ice mostly. Our results also suggest that the water-ice content could be estimated from radar measurements at different temperatures.