Detection and Microwave Imaging of Conducting Objects Buried Very Closely to the Air-Soil Boundary

Down-looking Ground Penetrating Radar (GPR) is an ultra-wideband electromagnetic sensor which has important applications such as IED and landmine detection, locating people in earthquake rescue operations, detection of archeological sites, mapping ice thickness or quantification of sedimentary structures in geophysical applications. The very first and important step in target detection by GPR is the removal of ground reflections caused by the air-soil boundary as these undesired signals are usually much stronger than the signals reflected and scattered from the buried targets. Ground reflections are well-known for their deteriorating effects on detection rate and false alarm rate in GPR applications. When a target is buried in a reasonable depth such as five centimeters or more, the ground reflections and the first returns from the buried object can be well separated in time, thus the removal of ground reflections turns out to be a standard procedure. However, if the burial depth is very small, the early returns from the target may be mistakenly removed together with the ground reflections. In such a case, a shallowly buried conducting target may go completely unnoticed. In this study, we will investigate the problem of detection and imaging of various conducting targets which are buried only one centimeter below the air-soil interface. The test targets are chosen to be a water-filled rectangular prism made of plastic; a thin rectangular prism coated by aluminum foil; two metal rods of the same length one with circular cross-section and the other one with a square shaped cross-section. After GPR-based measurements are recorded for these targets, a preprocessing method based on energy features and background removal will be used to eliminate air-ground reflections from the raw GPR A-Scan signals. C-Scan data sets, which are the collections of measured A-Scan signals recorded in cross-track and down-track directions, will be used for subsurface microwave imaging to sense the presence of the buried targets, and to figure out their shapes, if possible.