Resilient Terrain Navigation with a 5 DOF Metal Detector Drone

Micro aerial vehicles (MAVs) hold the potential for performing autonomous and contactless land surveys for the detection of landmines and explosive remnants of war (ERW). Metal detectors are the standard tool, but have to be operated close to and parallel to the terrain. As this requires advanced flight capabilities, they have not been successfully combined with MAVs before. To this end, we present a full system to autonomously survey challenging undulated terrain using a metal detector mounted on a 5 degrees of freedom (DOF) MAV. Based on an online estimate of the terrain, our receding-horizon planner efficiently covers the area, aligning the detector to the surface while considering the kinematic and visibility constraints of the platform. For resilient localization, we propose a factor-graph approach for online fusion of GNSS, IMU and LiDAR measurements. A simulated ablation study shows that the proposed planner reduces coverage duration and improves trajectory smoothness. Real-world flight experiments showcase autonomous mapping of buried metallic objects in undulated and obstructed terrain. The proposed localization approach is resilient to individual sensor degeneracy.