Fig. 4

The two-layer model adopted by this study. The surface and subsurface reflection are P_rs (W) and P_rss (W), respectively. R (m) and R_D (m) are, respectively, the altitude of the spacecraft and the true depth to the subsurface reflector. Both relative magnetic permeability μ and permittivity ε between SELENE and the Moon’s surface are assumed to be unity, while those of the 1st layer are unity and ε₁. The electrical conductivity of the 1st layer is σ₁, and the bulk permittivity of the 2nd layer is ε₂