An Experimental Study on Airborne Landmine Detection Using a Circular Synthetic Aperture Radar

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.Comment: 7 pages, 9 figure

Digital true time delay for pulse correlation radars

A novel concept for digital true time delay pulse correlation radars using digital programmable delay lines and monolithically integrated radar front-ends is investigated. The effects of quantization errors on side lobe level and deviation of beam direction due to the digital true time delay lines are evaluated by numerical simulations based on the performance of commercially available time delay units. To verify the simulation results, a compact 26 GHz active electronically steered linear antenna array consisting of 8 elements has been realized, which provides beamforming in both transmit and receive path. Measurement results and design details of this steerable radar sensor are presented in the experimental part of this paper

Airborne tripwire detection using a synthetic aperture radar

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 continuous-wave 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

Radar taking off: New capabilities for UAVs

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 inertial measurement units (IMUs)-including gyroscopes and accelerometers-barometric sensors, and the Global Navigation Satellite System (GNSS) are used. To sense the UAV's direct environment, e.g., for collision avoidance or fully automated flight, additional sensors are needed. State-of-the-art combinations of infrared, ultrasonic, and 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 affected by lighting conditions and contrast. With the help of a multichannel radar, the angular information may also be extracted

UAV-based ground penetrating synthetic aperture radar

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 4GHz 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

Implementation of a SAR demonstrator for automotive imaging

To fulfil the need for finer resolution automotive radar imaging, in this paper, a SAR demonstrator and processing algorithm at 77GHz are shown which represent a realistic low cost implementation for automotive applications. In the measurement setup section, the demonstrator is described along with how the strict requirements of synchronous radar measurements and trajectory information are fulfiled. A processing algorithm is also presented that is modelled for automotive applications, such that the measurements are processed in blocks, which represent sub-apertures, as they become available from the radar. This results in a faster processing time. Additionally the effect of the missing signals in azimuth, which occur because of hardware restrictions, is clarified and minimised using compressed sensing by recovering the missing signals. To verify the results delivered from the developed algorithm, the processed images are compared with those obtained from the time domain backprojection algorithm and the results were found to be in good agreement

Position acquisition for a multicopter-based synthetic aperture radar

Humanitarian demining is still mainly carried out by hand. The most trusted and widely used technical tool is probably the metal detector. However, these sensors are hand-held devices which are operated closely to the surface. To make the process of mine clearance safer, a ground penetrating synthetic aperture radar (GPSAR) was developed that can be operated on an autonomous flying unmanned aerial system (UAS). A key challenge of this system approach is the accurate position acquisition of the UAS. This paper compares a real time kinematic global navigation satellite system (RTK GNSS) and a total station with respect to UAS-based synthetic aperture radar (SAR) image processing. First, the systems and the associated signal processing chain will be briefly presented, then the trajectories and the processed SAR image will be compared

UAV-based polarimetric synthetic aperture radar for mine detection

In this contribution a polarimetric side-looking synthetic aperture radar (SAR) mounted on a unmanned aerial vehicle (UAV) is presented and discussed with respect to the detection and localization of landmines. As an example for an anti-personal mine a PFM-1 which contains an elongated aluminium rod was considered. Such anisotropic geometries exibit a polarization dependend radar cross section (RCS). Through a special configuration of three antennas, polarimetric SAR measurements involving a back projection algorithm could be implemented. This concept allows for the detection and furthermore the classification of such anisotropic objects. First field tests using a tachymeter for localization of the UAV over a snow covered meadow successfully demonstrated the performance by the detection of small metal rods depending on their orientation with respect to the flight path of the UAV. These experimental results were supported by simulations expressing the necessity of polarimetric measurements in combination with a distinct flight trajectory for a robust detection of certain landmines

Lightweight broadband antennas for UAV based GPR sensors

In this contribution two different types of broadband antennas namely a logarithmic-periodic dipole antenna (LPDA) and a transversal electromagnetic (TEM) horn antenna for ground penetrating synthetic aperture radar sensors are presented. These antennas are designed to be mounted on an unmanned aircraft vehicle (UAV). The antennas are evaluated in terms of their matching, radiation pattern pulse response and weight. Finally, an integration example of one of these antennas is shown on an UAV