Permittivity and density of lunar regolith estimated from LPR data. (a) Average propagation velocity of radar signal estimated from hyperbolas as a function of two-way travel time. (b) Depth-averaged permittivity of regolith at CE-4 landing site versus depth. (c) Permittivity of Apollo soil samples at 450 MHz as a function of density (Olhoeft & Strangway 1975). The dashed lines constrain the CE-4 permittivity range and the corresponding density range. (d) Inverted depth-averaged bulk density of regolith as a function of depth. The Apollo density models come from Carrier et al. (1991).