Ground-penetrating radar measurements of subsurface structures of lacustrine sediments in the Qaidam Basin (NW China): Possible implications for future in-situ radar experiments on Mars

Abstract The stratigraphic profile of paleolakes on Mars preserves a record of past climatic, hydrological and sedimentary environment. Radar could be used to detect the structure and distribution of buried lacustrine sediments. But orbiter radar sounders rarely detect the internal structure or the bottom of the ancient Martian lake deposits. Future Martian missions will employ ground-penetrating radar (GPR) onboard rovers to investigate the shallow subsurface structure of paleolake basins. In this case, ground experiments are necessary to test the potential of GPR detection. This study reports on GPR experiments operating at 100 MHz and 200 MHz carried out in the Qaidam Basin, one of the analogue sites for Martian paleolake environments, to detect the subsurface structure of lacustrine sediments and measure the relative permittivity of sediments with both laboratory instrument and GPR data. Two GPR measurements were performed on top of yardangs representing layered lacustrine sedimentary outcrops. Another survey site is a polygonal patterned ground, which is a common landform in the Qaidam Basin and on Mars. The observations revealed by GPR experiments show that (1) sediments of three sites have varied compositions, density and porosity, and have a wide range of relative permittivity values, from 1.56 to 4.56; (2) the detection depth of our measurements could reach 20 m; (3) The interfaces between sedimentary layers can be seen in radargrams, but reflectors in radargrams may not always match with exposed layers of the yardang outcrops due to the undetected change of permittivity values or thin thickness of layers; (4) A distinct and continuous reflector is observed beneath the polygonal terrain which we interpret as a subsurface layer with low water/brine content. Our ground experiments suggest that a similar GPR on Martian rover could detect the near-surface structure of lacustrine sediments, e.g. deposition anomaly, interfaces of drastic permittivity change such as buried ice/brine considering that the design frequency is close to our equipment.