Bulk density of the lunar regolith at the Chang'E-3 landing site as estimated from Lunar Penetrating Radar

Figure 2. Apparent range (R) between GPR antenna and a subsurface rock as a function of horizontal distance (x) along the survey line with different (a) antenna height, (b) target depth, and (c) relative permittivity. In (a) and (b), the relative permittivity of subsurface media is set to 3.0, a typical value for lunar regolith; in (b) and (c), the antenna height is set to 0.273 m as the case of CE-3 LPR.

Figure 3. (a) Eccentricity of hyperbolic curves produced by a subsurface rock as a function of relative permittivity for different rock depth, where the antenna height is set to 0.273 m as the case of the CE-3 LPR. The thick black curve represents theoretical eccentricity as a function of relative permittivity. (b) The relation between relative permittivity and rock depth, where the antenna height is 0.273 m. From left to right, the black curves represent a constant eccentricity of 1.01, 1.02, 1.05, 1.1, 1.15, … , 1.35and 1.4, and the blue curves from top to bottom correspond to a constant minimum apparent depth (dmin) of 0.1, 0.5, 1, 2, …, 8 and 9, respectively.

Figure 4. (a) Relative error in the estimated relative permittivity as a function of model input relative permittivity for different rock depths. (b) Relative error in the estimated relative permittivity as a function of model input relative permittivity with different uncertainty in antenna height, where the rock depth is set to 3.0 m. (c) Probability distribution of the estimated relative permittivity from Monte Carlo simulation (gray bars) and a Gaussian distribution (black line) with a mean relative permittivity of 3.1 and a standard deviation of 1.

Figure 5. (a) The processed LPR image along the CE-3 survey line after horizontal band removal, band-pass filtering, and compensation of geometrical spreading and dielectric attenuation, where bright tone indicates strong echoes, and gray denotes weak reflections. The red dots indicate the vertexes of the identified hyperbolic curves.  (b) The estimated relative permittivity and bulk density of the lunar regolith along the CE-3 survey line.

Figure 6. (a) Mean bulk density of the lunar regolith at the CE-3 landing region as a function of depth, where the dots are estimations from the CE-3 LPR observations, and the thick line is the best fits of the LPR estimations using an exponent function. (b) Bulk density profiles at the Apollo 15, 16, 17, and the CE-3 landing sites. (c) Lunar regolith bulk density profiles from Chang’E-3 LPR estimation (black), the Apollo core tube samples (red), and Diviner radiometer inversion (blue).