Wall Radar Research Articles

Sensing and Identifying the Improvised Explosive Device Suicide Bombers: People Carrying Wires on their Body

We examined the use of radar to detect humans wearing detonation wires as part of a suicide vest in suicide bombings in an effort to stop the bombing. Dogaru et al. (Computer models of the human body signature for sensing through the wall radar applications. Tech. Rpt. ARL-TR-4290, Army Research Laboratory, 2007) used numerical electromagnetic simulations to show ways to use radar backscatter to detect humans carrying weapons behind walls. We developed Numerical Electromagnetic Code (NEC) simulations for the radar cross-section of wire configurations appropriate to the human body and compared them to the radar cross-section simulations for the human body done by Dogaru et al. We also used GunnPlexer Doppler radar at 12.5 GHz to collect laboratory experimental data from standoff distances of 2—8 meters from the following: human subjects, human subjects wearing a wire loop, and human subjects wearing a simulated vest with wire loops. We performed numerous experiments with both horizontal and vertical polarization (HH and VV), analyzing the data after each experimental run. We developed metrics from examining our experimental data of the radar cross-sections that could be used in building models to more accurately find subjects wearing wires. We wanted a metric to provide us with better statistical detection rates. We found several metrics that improved our ability to detect persons wearing wires. We discovered our best metric was the VV/HH ratio of radar cross-section. From our empirical modeling, we found that the ratio for people wearing wires was statistically different from people without wires at a level of significance of α = 0.05. Using this metric, we built a Monte Carlo simulation model that generated a crowd of people and randomly picked those with wires on their person. We used our metric and a threshold value, which we determined experimentally, to distinguish the persons with wires from those without wires. We found from our simulation that our metric provided a success rate of detecting persons wearing wires of approximately 83.4%, based on running 36,000 trial runs in Excel. The rate of false alarms, where the metric in the simulation model picked a subject who was not wearing wires as a suspect wearing wires, was reduced to 28%. Using the work of Dogaru et al. and our NEC simulations of wire harnesses in the 0.85—1 GHz range, we found that the radar cross-section ratio (body with wires/body without wires) varied from 11 dB for 1—1.15 GHz VV polarization to —5.5 dB for 0.85—1 GHz HH polarization. This frequency range was the best in the range 0.5—9 GHz. From our research we showed that we can be successful in finding viable metrics for detecting wires on people using radar observations. This preliminary research and the exciting results it produced encourages one to think that suicide bombers can be found prior to their detonation of their bombs and at ranges that are relatively safe.

EVALUATION OF TRM IN THE COMPLEX THROUGH WALL ENVIRONMENT

Practical interests arising from behind-the-wall target detection, surveillance and reconnaissance etal. claim for high capability of imaging in complicated environments. Time Reversal Mirror (TRM) technique, making use of the principle of reciprocity, emerges as a promising way to deal with such complex problem. In this paper, we investigate TRM in the ultra-wideband (UWB) through wall radar imaging (TWRI) through numerical simulation. The probing region is a square room, with walls of rough surface and random media parameters. TRM is used to image the target settled in the room. We evaluate the degradation of the images when the aperture of the array is decreased or the received signals are contaminated by noises. The back projection (BP) algorithm is employed here as a comparison for imaging quality. For the case in which the random walls are changed between the forward and inverse phase of time reversal, we check the imaging stability and applied an averaged Green's function to improve the imaging quality. Finally, some interesting conclusions are drawn.

APPLICATION OF TRM IN THE UWB THROUGH WALL RADAR

Time Reversal Mirror (TRM) technique, in the virtue of its high resolution in the heterogeneous media, has been widely applied in the area of acoustics and electromagnetics. In this paper, the technique is developed to imaging targets in the contest of ultra-wideband (UWB) through wall radar (TWR) through numerical simulation. We firstly consider the technique to image targets behind a single-layered wall and then extend to the multi-layered wall. The simulation results have reported the imaging capability of the algorithm and its powerful use for TWRimaging. For concerning the image stability, we investigate the TRM images for the case in which there is a mismatch between the walls associated with the forward and inverse phases of time reversal. The back projection imaging algorithm is compared here at the same time for a contrast of the imaging quality. Finally, some conclusions are drawn.