Study of Variability of Complex Permittivity of Terrestrial Analogue of Lunar Soil (TALS) Having Different Percentage of Water at Microwave Frequencies

Abstract

Knowledge of complex permittivity of lunar soil at lunar pole temperature (−196 °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 $(\varepsilon ^\prime)$ and imaginary part $(\varepsilon ^{\prime\prime})$ ] of terrestrial analogue of lunar soil (TALS) has been measured at room temperature (30 °C) and lunar pole temperature (−196 °C) using liquid nitrogen $(\mbox{LN}_2)$ 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 $(\varepsilon ^\prime)$ and imaginary part $(\varepsilon ^{\prime\prime})$ 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 °C than at −196 °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 °C and −196 °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.