| Summary: | Abstract Bulk density of the lunar regolith is a key factor affecting its geophysical and geotechnical properties. In this study, a new method for estimating the bulk density of the lunar regolith is developed based on the geometric characteristic (i.e., hyperbolic shape) of radar echoes in ground penetrating radar (GPR) image. As an application, bulk density of the lunar regolith at China's Chang'E‐3 (CE‐3) landing site is estimated using the Lunar Penetrating Radar data. In total, 57 hyperbolas are identified in the Lunar Penetrating Radar image and their eccentricities are used to estimate relative permittivity of the regolith. Then, bulk density of the lunar regolith is estimated using an empirical relation through its dependence on relative permittivity. The results show that bulk density of the regolith at the CE‐3 landing site increases with depth from 0.85 g/cm 3 at the surface to a steady‐state value of 2.25 g/cm 3 at 5 m, with an average gradient much smaller than that based on the Apollo regolith samples. The bulk density corresponds to a regolith porosity of 74.5% at the surface and 32.3% at 5 m depth over the CE‐3 landing region. Given that the landing site is only ∼50 m from the east rim of a 500 m diameter crater, named as Zi Wei, the steady‐state bulk density indicates a 29% volume fraction of subsurface rocks within the continuous ejecta of this crater.
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