Through-wall radar image reconstruction based on time-domain transient signals in the presence of noise

Abstract

Through-wall radar imaging has become a keen research topic in recent years. This is due to the emphasis on homeland security, which involves many key areas such as gathering intelligence, concealed weapons detection and domestic counter-terrorism. Other applications of through-wall radar imaging include urban warfare, hostage rescue scenarios as well as search and rescue operations. This paper investigates the reconstruction of the position of objects behind walls based on the time-domain transient signals generated from a simulation program. An electromagnetic wave simulation program, using the finite difference time domain (FDTD) (1) method was used to model the transient signals as they pass through walls and interact with objects of different materials. The reflected signal was then recorded by receivers at various positions behind the wall. The difference in position between the receivers results in varying time-delays in the received signals. As a result, when the received signals are combined to form an image of the objects on the other side of the wall, the position and shape of the objects are inaccurate, resulting from the different time-delays of the radar returns. Migration techniques such as normal move-out (NMO) are used to compensate and reconstruct a more accurate shape of the objects. Time-delay correction applied to the signals is dependent on the ability to detect the presence of the transmitted pulse. This problem becomes increasingly difficult in the presence of noise. Pre-processing techniques such as low-pass filtering and Wiener filtering were applied to improve the signal detection. Keywords Finite-Difference Time-Domain (FDTD), Normal Move-out (NMO), Through-Wall Radar Imaging.