Simulation analysis of microwave emission from lunar subsurface for SAR radiometric mode dual frequency (L/S Bands) observations onboard Chandrayaan-2

Abstract

Dual Frequency Synthetic Aperture Radar (DFSAR) (at L and S bands) onboard Chandrayaan-2 (CH-2) has an experimental radiometric mode operation. This paper evaluates the utility of such experimental observations of lunar studies for the future missions. Owing the deeper penetration of L and S bands frequencies, a multilayered microwave radiative transfer model coupled with thermal model has been used to account for the microwave thermal emission or the brightness temperature (TB) from the lunar subsurface at 1.25 GHz and 2.5 GHz frequency. As the dielectric property of lunar regolith is the primary deciding factor of depth of penetration of microwaves into lunar surface, the TB simulated using different dielectric models are compared with the observed TBs of Chang′E-2/Microwave Radiometer (MRM) and selected the dielectric model which consider both frequency and metallic content (Montopoli et al. (2011); Feng et al. (2020); Siegler et al. (2020)) in this study. DFSAR/CH-2 operating frequencies such as 1.25 GHz and 2.5 GHz can be used for sounding dielectric discontinuity due to the presence of water ice, high minerals or densely packed rocky medium than thermal sounding as microwave thermal emissions at these channels are not sensitive to surface temperature, as it is invariant with time for depth below 50 cm. Hence these frequencies are potential tool to study the sub-surface characteristics such as determination of lunar regolith thickness and for the discrimination of subsurface material type.