摘要：Dielectric properties of the subsurface layers provide important clues to material compositions beneath the surface.The Mars Reconnaissance Orbiter (MRO) Shallow Radar (SHARAD) observed clear subsurface reflections in the Elysium–Utopia region, where morphological features such as impact craters with rampart ejecta suggest the possible presence of volatiles, but the permittivity of the subsurface unit beneath the surface strata has not been derived yet to provide independent evidence for or against the presence of water ice.In this paper, we employed a three-layer model consisting a surface mantling layer (layer I), a shallow subsurface layer (layer II), and a deep subsurface layer (layer III) to invert the permittivity of layer III, which considers the surface roughness and attenuation of radar waves in layer II.The obtained permittivity and loss tangent in the study region confirm that the materials of layer II are dense basaltic flows.Then, the permittivity of layer III is derived as 2.6 ± 0.9, suggesting that subsurface water ice may be present, or a layer of dry and low-density deposits exists beneath the basalt layer.The hypothesis could be further tested by the ground-penetrating radar of China's first Martian mission, to be launched in 2020.Our results also show that the surface mantling layer included in the model is essential in the calculation of permittivity values.
