  Many countries in the world are contaminated with landmines. Several thousand
casualties occur every year. Although there are certain types of mines that can
be detected from a safe stand-off position with tools, humanitarian demining is
still mostly done by hand. As a new approach, an unmanned aerial system (UAS)
equipped with a ground penetrating synthetic aperture radar (GPSAR) was
developed, which is used to detect landmines, cluster munition, grenades, and
improvised explosive devices (IEDs). The measurement system consists of a
multicopter, a total station, an inertial measurement unit (IMU), and a
frequency-modulated continuous-wave (FMCW) radar operating from 1 GHz to 4 GHz.
The highly accurate localization of the measurement system and the full
flexibility of the UAS are used to generate 3D-repeat-pass circular SAR images
of buried antipersonnel landmines. In order to demonstrate the functionality of
the system, 15 different dummy landmines were buried in a sandbox. The
measurement results show the high potential of circular SAR for the detection
of minimum metal mines. 11 out of 15 different test objects could be detected
unambiguously with cm-level accuracy by examining depth profiles showing the
amplitude of the targets response over the processing depth.
