An Improved Hyperbolic Method and Its Application to Property Inversion in Martian Tianwen-1 GPR Data

Abstract

On 15th May 2021, the Tianwen-1 (TW-1) successfully landed on the surface of Mars within the southern Utopia Planitia. It delivered a rover named Zhurong equipped with ground penetrating radar (GPR), a device that can investigate the thickness and structure of the geological layers below the martian surface. The hyperbola method is commonly used for extracting dielectric property variations with depth from GPR data to aid the interpretation of the subsurface structure and material composition. This study analyzes the advantages and drawbacks of three hyperbola methods with different geometric models. Next, it proposes a new method aiming to use the highly precise, yet complex geometric model and address issues caused by its solving process. We also analyze the influencing factors contributing to measurement errors and design corresponding criteria for measurement point selection to mitigate errors. The average error of the proposed method is less than 5% for a depth of up to 9 m. We employed the proposed method to obtain the dielectric constant distribution in the shallow surface layer of the TW-1 landing zone to a depth of up to 16 m. The dielectric constant is mainly concentrated between 2 and 8 m and increases gradually with depth. Below 2 m, the dielectric constant is about 5.1 and the density is about 2.5 g/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The stratification and density variation can be inferred from the dielectric constant distribution diagram.