WISDOM GPR calibration and data processing methods applied to field test data

The ExoMars Rosalind Franklin Rover exobiology mission is now scheduled for launch in 2028 to search for traces of past or present life in the shallow subsurface of Oxia Planum. The rover is equipped with a drill that can take samples down to 2m, where organic molecules and possible biosignatures are likely to be preserved. The WISDOM GPR has been designed specifically for the objectives of the ExoMars mission. It will provide scans of the Martian subsurface down to a few meters, which, together with the other rover instruments, will help to understand the geological context of the landing site.

Rover-based GPR systems typically use antennas mounted at some distance from the ground. Over the large signal bandwidth, this fixed antenna-to-ground distance varies from a fraction of a wavelength to several wavelengths and can cause strong frequency-dependent coupling with the rover structure. Even with careful instrument design, additional coupling in the receiver chain cannot be avoided. These types of coupling, as well as the frequency-dependent main lobe response of the antenna, depend on the environment in which the rover is located (e.g. the dielectric properties of the ground), so that existing pre-calibrations of the radar system, e.g. in the laboratory, are of limited validity.

The algorithms we developed for data processing and system calibration can help to analyze and mitigate frequency-dependent coupling effects, separate the instrument transfer function and increase resolution, and thus improve the interpretation of surface and subsurface echoes. They will eventually be implemented in the pipeline that will be used to calibrate and interpret Martian data.

The proposed signal and data processing algorithms are validated on simulated data, on data collected during indoor measurement campaigns and on data collected during field tests. This paper focuses on the application of data processing algorithms to data collected during a field campaign in glacier and permafrost regions on Svalbard.