Modern consumer and industrial unmanned aerial vehicles (UAVs) are easy to use flying sensor platforms. They offer stable flight, good maneuverability, hovering, and even waypoint flights in autopilot mode. For stabilization and localization sensors such as internal measurement units (IMUs) including gyroscope and accelerometer, barometric sensor, and global navigation satellite system (GNSS) are used. To sense the direct environment of the UAV, for instance for collision avoidance or fully automated flights, additional sensors are needed. State-of-the-art combinations of infrared sensors, ultrasonic sensors as well as vision based sensors (monocular and/or stereo vision) capture the close vicinity. Using radar sensors is advantageous, as they are able to directly sense range and velocity and are not prone to lighting conditions and contrast. With the help of a multi-channel radar, the angular information can also be extracted. UAVs can lift a considerable payload with respect to their size. All these characteristics combined with radar sensors make them a promising tool for a large variety of applications.

A novel approach for anti-personnel landmine detection using an unmanned aerial vehicle (UAV) in combination with a ground penetrating synthetic aperture radar (GPSAR) is presented. The objective of the system is to accelerate the process of land release in humanitarian demining. Suspicious objects shall be detected by the radar and marked for further investigations using different sensor principles. The ground penetrating radar (GPR) module consists of a 1 GHz to 4 GHz side-looking frequency modulated continuous wave (FMCW) radar, a radar and lidar altimeter, and a real time kinematic global navigation satellite system (RTK GNSS). The image processing is done offline using a back-projection algorithm. In the theoretical part of this paper the system partitioning, the sensor module, and the position accuracy requirements are briefly described. In the experimental part of this paper synthetic aperture radar (SAR) measurements are presented.

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Anti-personnel fragmentation mines are relatively large metallic mines, which are only partially buried and often triggered by a metallic tripwire. In humanitarian mine clearance, the search for the wires is usually carried out manually. As a new approach, an airborne system for the detection of tripwires using a synthetic aperture radar is presented. The system consists of an industrial multicopter, a frequency-modulated continuouswave radar, and a real time kinematic global navigation satellite system. For image formation, a back-projection algorithm is used. Measurements with tripwires attached to a dummy mine successfully demonstrate the functionality of this system approach. In addition, the influence of wire length, vegetation, and incidence angle are investigated. It is shown that several overflights with different directions of flight are required to detect randomly oriented tripwires.

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