978-1-4244-4605-6/09/$25.00 ©2009 IEEE An Ultra-Wideband High-Dynamic Range GPR for detecting buried people after collapse of buildings Gilberto Grazzini, Massimiliano Pieraccini, Filippo Parrini, Alessandro Spinetti, Giovanni Macaluso, Devis Dei and Carlo Atzeni Dept. of Electronics and Telecommunications University of Florence Via Santa Marta 3, Firenze, Italy gilberto.grazzini@unifi.it Abstract—An ultra wide band high dynamic range GPR radar - has been tested for buried victims detection. After a building collapse, for example due to an earthquake, the priority of search and rescue teams is to localize people trapped under debris. Several tools are available to help the detection of buried humans, such as micro-cameras, high sensitivity microphones, and so on. Many of these tools present some limitations such as low penetration depth and high susceptibility to external noises. In this paper the authors test the use of an Enhanced Ultra Wide Band (UWB), Continuous Wave Stepped Frequency (CW-SF) Ground penetrating radar as rescue equipment. The radar has been experimented both in controlled environment, and in a real test site, at the Fire-fighters Station of Pisa, Italy. Keywords-component; UWB; CW-SF; Survivors research. I. INTRODUCTION In case of natural disaster, such as earthquakes, avalanches, and also in cases of terrorist attacks, the speed of the rescue team is crucially important. In these situations even few minutes can be too much for a survivor trapped under debris coming from a destroyed building. Fire-fighters brigades are trained as rescue team in these situations, they are equipped with numerous tools to localize potential survivors, like snake- camera, high sensibility microphone or dog units. But usually these tools show some limitations. Snake-cameras for example, are very efficient tools to investigate not accessible area, they can fit in very small hole and reach very deep positions, but the investigation area is very small. Unlike snake-cameras, high sensitivity microphones can investigate larger area, but on the other hand these devices are very sensible to environmental disturbances, even a light wind blowing through the cable can waste the measurement. Nowadays search and rescue (SAR) dog-units are considered the most reliable “tool” for survival search. All humans constantly emit microscopic particles producing human scent, dogs are trained in order to trace these scents and locate the human emitting such odour. Unlike technological tool, dogs are not sensible to environmental noise, and can also move very rapidly all over the disaster area. On the other hand, odours can get to surface even far from the zone where the survivor really is, because microscopic particle can follow unknown subsurface channels, therefore dogs are used to reduce the research area to few tens of square meters. In recent years microwave radar sensors for trapped human detection have gained a lot of attention. Both CW [1] and UWB pulse radars [2] have been employed for survivor detection, the former using the doppler effect while the latter relies on the difference of the time-of-arrival of the backreflected wave due to the movement of the chest of the person. Usually UWB system show better performances compared to the CW systems, mainly because the range resolution capability, given by the frequency diversity, allows a better discrimination of the target signal with respect to the static clutter given by the antenna coupling and the environment reflections. This work describes the use of a Stepped Frequency Continuous Wave (SF-CW) radar for buried victim detection. This system uses a UWB radar technology different with respect to pulsed radar, which can guarantee higher time stability, which will be demonstrated to be a crucial characteristic for this specific application. The description of the requirements, and the characteristics of the system are described, along with results obtained in a simulated test site used for rescue team training. II. A STANDARD GPR APPROACH TO THE PROBLEM Standard GPR measurements are usually carried out performing linear scans on the surface of the investigated area. The subsurface medium usually has rather homogeneous electrical characteristics. Moreover, typical GPR targets are air, water or gas filled pipes, electrical cables or optical fibres. In this application the presence of the subsurface targets is detected exploiting the dielectric contrast of buried targets, where the linear scanning helps finding the positions of such targets. In this measurement configuration the issues arise from the strong electromagnetic soil attenuation that limits the capability to detect deep targets. However, it is not possible to employ such a method for survivors’ detection mainly due to two reasons. First, in the case of survivors’ search the investigated medium is usually very inhomogeneous, since debris are composed by concrete, bricks, stones, plastic, wooden scraps, reinforced bars and so on. Each material exhibits different dielectric characteristics and, even though microwave dielectric properties of human body [4] may be rather different with respect to such materials, it is impossible to detect buried survivors employing the dielectric contrast features. Second, it is impossible to perform a traditional linear scan on debris. This means we lose the capability to detect the horizontal position of the target and we also lose the signal integration that is obtainable performing linear scans.