Analysis, data processing and retrieval of Mars surface properties from Mars Express bistatic radar experiments

Bistatic radar experiments have proven to be a powerful technique for remote planetary exploration across the Solar System, with multiple bistatic campaigns conducted on the Moon, Venus, Mars, as well as distant celestial objects such as Titan and Pluto. The Mars Express mission, during its 22 years of operations, performed more than 70 downlink BSR experiments. Analysis of the reflected echoes from the surface provides information about near-surface roughness statistics, measured in terms of RMS slope, and dielectric constant. These surface properties can help identify potential landing sites for future missions and are crucial to characterize the structural and compositional properties of the near-surface environment, expanding our overall knowledge about the Martian surface. The purpose of this work was the analysis of a selected subset of bistatic radar experiments from the publicly available Mars Express dataset. The investigation focused on four experiments and was restricted to the X-band dataset due to its higher signal-to-noise ratio. Measurements of the dielectric constant were consistent with the expected values for the Martian near-surface (2.5-4) in the equatorial and tropical latitudes, while values slightly below the expected ones were reported in the north polar region, with an average value of 2.42 over the north polar cap and values around 2.24 over Vastitas Borealis. Results of permittivity were always below 4.5, excluding high density clay or basaltic bedrock exposed in the near-surface, while suggesting the presence of porous materials, such as sandy deposits. RMS slope measurements mainly exhibited a behavior compatible with a beam-limited regime. Future work could be aimed at refining and/or adding further steps to the analysis. For example, a comparison between the S-band and X-band dataset would be particularly insightful for the characterization of the near-surface structure and to enrich our understanding of the Martian surface.