2:15 PM - 2:30 PM
[PPS23-01] High permittivity regions in Oceanus Procelluram and Mare Imbrium found by SELENE (Kaguya)
Keywords:SELENE(Kaguya), Lunar Radar Sounder (LRS), permittivity, Oceanus Procelluram, Mare Imbrium, Digital terrain model (DTM)
Analyses Method: The global distributions of the intensity of the off-nadir surface echo in a frequency range of 4 - 6 MHz in an incident angle range from 10 to 20 degrees were derived from the SELENE/LRS dataset. The median of off-nadir echo intensities were derived in 360 x 180 areas of 1 degree (longitude)x 1 degree (latitude). In addition, we have derived the global distribution of the surface roughness parameters. The RMS height ν can be derived from the SELENE TC/DTM. If we assume the self-affine surface model, the roughness parameters H and s can be obtained by the least square fitting: ν = s ΔxH in a baseline length Δx range from 30 m to 3 km. The off-nadir surface echo power was then calculated by using the radar equation. Assuming KA, the backscattering coefficient in the radar equation can be obtained from the roughness parameters H, s [Bruzzone et al., 2011]. In calculation of the expected echo powers, we have to assume some effective permittivity also. We compared the observed and calculated echo powers with changing effective permittivity assumption, and determined the most plausible effective permittivity.
Results: By applying the analysis method mentioned above, we could obtain the observed and calculated off-nadir surface echo powers. Based on them, we could estimate the effective permittivity of the lunar surface materials. The estimated effective permittivity is 2 - 3 in the highland, 3 - 4 in the maria. In addition, it was found that there areas whose effective permittivity reaching ~5 in the eastern part of Oceanus Procellarum and the western part of Mare Imbrium.
Discussion: By using the estimated effective permittivity of the lunar surface, we can derive the bulk density of the lunar surface materials. The derived bulk density is 1.2 - 1.8 g/cm3 in the highlands, 1.8 - 2.3 g/cm3 in the maria, and approximately 2.6 g/cm3 in the high-permittivity areas in Oceanus Procellarum and Mare Imbrium. The differences of estimated bulk density among the previous studies [Wiezorek et al., 2013; Carrier et al., 1991] and this study could be explained by the depth dependence of the bulk density of the lunar surface soils and rocks. The areas of high permittivity in the eastern part of Oceanus Procellarum and western part of Mare Imbrium coincide with young lava flow units in PKT region. We can consider two possible reasons: (i) The regolith layer is thinner than other mare regions due to short exposure to the meteorite impacts. (ii) The bulk density is higher than other mare regions due to high abundance of the ilmenite.