Fraunhofer Institute for High Frequency Physics and Radar Techniques FHRThe threat posed by landmines on the ground is increasing in light of wars and conflicts worldwide. In efforts to clear landscapes of mines, finding explosive devices in the soil poses an enormous challenge: a large share of objects are empty oil cans, broken shopping carts, or simply an old tin. There are also cases where, when placing improvised explosive devices, scrap is laid out to hinder the enemy from locating them. This is where the work of the researchers led by Dr. Christian Bräu, group leader UWB radar at Fraunhofer FHR in Wachtberg, comes in.
The Fraunhofer FHR team uses all high-tech options and relies on ultrawideband radar. Radar can detect non-metallic objects as well; after all, landmines or detonation devices like canisters filled with fertilizer are almost always made of plastic. This gives the technology clear advantages over classical detection methods. The currently developed ground-penetrating radar sensor at the institute operates in a frequency range from 400 MHz to 6 GHz. The low frequencies allow the electromagnetic waves to penetrate deeply into the ground. The wide bandwidth, in turn, improves the resolution and level of detail of the scanned objects, supporting a well-founded decision basis for on-site users.
Further progress is achieved by Bräu and his team through a novel combination of polarimetric and multi-static antennas. In the multi-static antenna arrays, one antenna transmits the signal and up to six antennas receive the reflected signals from the ground. The different angles at which the reflected waves arrive create an exact image of the objects hidden in the ground. For even greater accuracy, the polarimetric antenna technology provides an added advantage. Bräu explains the approach: “We exploit the phenomenon that objects that reflect radar waves also alter their polarization, i.e., the plane in which the electromagnetic wave oscillates. The altered polarization data provide us with additional information about the geometry and dimensions of the respective object.” A clear added value for practical object classification.
With the experimental sensor currently being developed at Fraunhofer FHR, the polarimetric and multi-static signal processing are combined. “With this, we hope to achieve improved detection of buried threats in challenging environments in the future, thereby saving lives and limbs,” Bräu concludes.