Dense Rocks With Smooth Surfaces in Martian Regolith Revealed by Polarimetric Analysis of GPR Data: A Case at Tianwen-1 Landing Site, Mars

This article reports the results of full-polarimetric Mars Rover Penetrating Radar (RoPeR) data acquired by the Zhurong rover of China's Tianwen-1 (TW-1) mission. A modified Freeman decomposition method is applied to the analysis of RoPeR data. By separating different polarimetric scattering components, an imperceptible interface previously obscured by different scattering signals is determined. Besides, an artifact in the signals generated by the double-time reflected signals between the ground and the rover body is identified via correlation analysis. Consequently, a double-layered structure of the Martian regolith to a depth of 3 m is revealed. The shallow layer and deep layer show strong volume scattering power and double-bounce scattering power, respectively, indicating their differences in structure. According to the results of the numerical test, the high-strength signals from the Martian surface are generated by the dense rocks and the undulating terrain, whereas the strong volume scattering components in the regolith are generated by piles of gravel. Besides, a kind of isolated dense rocks with a smooth surface and high loss tangents is identified in the regolith, which is interpreted as the platy duricrusts observed to be formed by aqueous activities. The results demonstrate that the Martian regolith structure at the TW-1 landing site is highly heterogeneous and that aqueous activities may have contributed significantly to it.