High-frequency subsurface-penetrating radar investigation of the shallow subsurface at the Zhurong landing site

Abstract

The shallow subsurface at the Zhurong rover landing site records recent geological processes under Late Amazonian conditions. The Rover-mounted Subsurface Penetrating Radar (RoSPR) on board the Zhurong rover provides a unique opportunity to investigate the fine-scale geological structures of the shallow Martian subsurface in southern Utopia Planitia. Our objectives are to constrain the fine-scale structure and electromagnetic properties of the shallow subsurface from both global and local perspectives and to infer the dominant modification processes at the landing site. We processed and analyzed the RoSPR high-frequency channel data using a workflow that included microwave tomographic imaging and loss tangent estimation based on energy attenuation. To identify subsurface scattering characteristics, we applied full-polarimetric Freeman decomposition to the radar data. The average loss tangent of the shallow subsurface is 0.0071 ± 0.0018, highlighting significant spatial heterogeneity in electromagnetic properties. At the global scale, radar reflection intensity shows a systematic attenuation trend consistent with the north-to-south topographic gradient along the traverse and correlates with local topographic undulations in most segments. This pattern likely reflects variations in weathered layer thickness controlled by topography-driven aeolian erosion and deposition. At the local scale, six discrete subsurface structures, including three buried impact craters, are identified across multiple perspectives (geometry, attenuation, and polarimetric signatures). Freeman decomposition reveals that volume and double-bounce scattering are the dominant mechanisms within these features, implying the presence of buried debris and complex infilling materials. Our findings suggest that while large-scale tectonic activity has been minimal in the Late Amazonian, the Martian surface has undergone extensive burial and modification processes dominated by aeolian activity.