Multi-frequency synthetic-aperture imaging with a lightweight ground penetrating radar system

Ž . The detection of buried objects, particularly hazardous waste containers and unexploded ordnance UXO , has gained significant interest in the Unites States in the late 1990s. The desire to remediate the thousands of sites worldwide has become an increasing concern and the application of radar to this problem has received renewed attention. The US Ž . Department of Energy’s Special Technologies Laboratory STL , operated by Bechtel Nevada, has developed several Ž . Ž . frequency-modulated, continuous-wave FM-CW ground penetrating radar GPR units. To meet technical requirements for Ž . higher-resolution data, STL and the University of California, Santa Barbara UCSB is investigating advanced GPR hardware, signal processing, and synthetic-aperture imaging with the development of an innovative system. The goal is to design and fabricate a lightweight, battery-operated unit that does not require surface contact, can be operated by a novice user, and can achieve improved resolution. The latter is accomplished by using synthetic-aperture imaging, which forms the subsurface images by fully utilizing the data sequences collectively along a scan path. We also present the backward propagation algorithm as the basic structure of the multiple-frequency tomographic imaging technique, and the conventional Ž . fast Fourier transform FFT method which can be described as a degenerated case of the model where the computation procedure is approximated under the narrow-beam assumption. q 2000 Elsevier Science B.V. All rights reserved.