Tunnel and lava-tube detection with magnetic Ground-Penetrating Radar

Lunar lava tubes may provide crucial insights for geological and biological research, particularly in understanding formation processes and any resident organisms. Geophysical techniques such as ground-penetrating radar (GPR) for mapping underground voids have the potential to be adapted and optimised for exploration in the arid lunar environment. With size and weight at a premium for space missions, we investigated means for shrinking GPR antennas. With collaborators, we have successfully designed, constructed and tested magnetic transmitters and receivers. This paper describes a ferromagnetic-cored magnetic dipole antennae (Named MAPRad for Magnetic Antenna Penetrating Radar) that are a fraction of the size of conventional half-wave electric dipole antennae. The transmitter antenna design and testing will be discussed in a future paper. Magnetic dipoles also have wider bandwidth than electric dipoles, beneficial for optimizing the resolution-depth penetration trade-off with compact antennas that can be mounted on a planetary rover. Due to the electrically resistive nature of basaltic lava flows, adapted GPR methodology can be tested on terrestrial lava tubes. The MAPRad prototype receiver has shown comparable depth penetration and resolution to conventional electric field GPR systems. Data obtained from field surveys has been used to compare the MAPRad magnetic prototype with the UltraGPR electric system, revealing similar operational capabilities. The MAPRad prototype successfully detected lava tubes with diameters of 10 meters or larger. Further testing is required on smaller targets such as tunnels to define resolution in both terrestrial and lunar environments.