12:00 PM - 12:15 PM
[PPS08-12] Feasibility study of detection of the lunar subsurface ice with UHF-band GPR based on FDTD electromagnetic simulation
Keywords:Lunar polar exploration, Lunar water ice, Ground penetrating radar (GPR), Finite difference time domain (FDTD) method
In this study, we used Meep code [Oskooi et al., 2010] for FDTD simulation. The simulation space with a size of 0.25 m x 1.25 m is divided into meshes with a size of 0.3 mm x 0.3 mm. The uppermost part with a height of 0.5 m is filled with vacuum (permittivity: 1). The second part with a thickness of 0.5 m is filled with dry regolith, basalt (permittivity: 7) including voids (vacuum). The lowermost part with a thickness of 0.25 m is filled with several kind of media such as (i) cavity (vacuum), (ii) rocks (basalt without pores), (iii) pure ice (permittivity: 3), and (iv) icy regolith, regolith whose voids are filled ice. The porosity of the dry and icy regolith layers was determined based on the report from Apollo missions on the vertical profile of the bulk density of the lunar subsurface soils up to depth of 3 m [Carrier et al., 1991]. Chirp pulse in a frequency range from 0.5 to 3 GHz was transmitted for 167 ns from 0.4 m above the dry regolith surface. The electromagnetic fields in simulation space were evolved with time step of 0.52 ps. At the transmission point, the waveform of electric field component of the echoes was recorded at an interval of 33 ps.
Calculation results suggests that subsurface echoes from (i) cavity, (iii) rocks, and (iv) icy regolith at a depth of 0.5 m can be detected with enough echo powers while the echo power from (iii) pure ice were as large as volume scatters due to inhomogeneity in the regolith. They are a little different from the results of our previous calculation performed in a frequency range 1-15 GHz with subsurface materials at a depth of 0.1 m: The echo powers from ice and icy regolith were as large as volume scatters. We can consider that the difference is from (a) the decrease of the volume scatters power by changing the operation frequency range, and (b) the depth dependence of permittivity contrast in inhomogeneous regolith.