Theoretical and Experimental Investigations on the Performance of Ground Penetrating Radars in Challenging Operational Conditions

In various important applications, Ground Penetrating Radar (GPR) instruments are demanded to operate in particularly challenging conditions, e. g., for the detection of variously-sized and shaped buried rocks in the shallow planetary subsurface, with close Tx/Rx antennas placed at the soil interface (as in the planned ESA "ExoMars" mission, having a GPR onboard an on-site rover). In such cases, the GPR should be able to locate properly scatterers at depths where the usual far-field operation could no longer be fulfilled and the relevant performance depends in a much more involved fashion on various physical parameters. This kind of problem is analyzed here by applying different compared approaches. A specific laboratory setup has been realized, with different commercial GPR systems working on an artificial dielectric box with buried scatterers. Based on proper processing of the measured radargrams, the depth of shallow subsurface rocky blocks in a sandy soil has been estimated in connection with the different GPR features. The validity of the results has been checked with suitable reference data, considering the theoretical frame to take into account various critical setup parameters (host medium features, geometrical and physical characteristics of the inclusions, GPR operating wavelengths, antenna separation, etc.). Further useful information has been derived by suitably implementing a full-wave numerical approach, able to accurately study the features of the waves detected by the GPRs with flexible parameterization. Helpful and reliable criteria can be achieved for proper design of such type of instruments in future planetary missions.