<title>Development status of a stepped-frequency ground penetration radar</title>

Abstract

The development status of two Stepped-Frequency Ground Penetration Radars (SFGPR) is presented. The equipment described includes a unit that operates over the 1 to 3 GHz RF band and is inten&d for shallow buried mine detection, and a unit that operates over the 150 MHz to 1 GHz RF band and intended for buried waste site characterization to depths of 7 meters. The SFGPR uses coherent high-range resolution radar processing methods to develop a radar-surface-position by slant range (depth) display. An extension of coherent synthetic aperture radar (SAR) imaging techniques that can yield 2-D and 3-D subsurface imaging is also presented. Results achieved to date are presented in 2-D for the high-frequency system and 3-D for the low-frequency system. BACKGROUNDThe development of GPR has not had a significant amount of progress in the last 20 years simply because of the difficulty of the problem: penetration of an extremely attenuative medium, that is, one of which complete characterization is virtually impossible. Thus, analysts have been faced with examining signals from GPR systems that are immersed in the clutter of ai unknown distorting nature. Adding to this has been the difficulty of the inadequate radar hardware itself. Signal generation and transmission quality, receiver noise, and dynamic range are but a few of the lacking features of available equipment.It is in this hardware area that the present paper attempts to avail the readers of an approach that has the distinct possibilities of improvement. The stepped-frequency radar concept has been available for many years, but cost and hardware availability has kept it from being a truly viable solution. Technology in recent years has improved the hardware availability issue and, to some extent, the cost.The chief advantages of stepped-frequency radar lay in the ability to obtain greater sensitivity, greater instantaneous dynamic range, and better iransmitted spectral control. However, these are exactly the features needed to improve GPR signal returns. After all, nothing can be done about the confusing medium of transmission, but the radar signal itself can be made cleaner and be received by better equipment that may make processing and understanding a bit easier. MINE DETECTION RADARColeman Research Corporation (CRC) has been working a Defense Advanced Research Projects Agency (DARPA)-sponsored program, in conjunction with Ft. Belvoir, to design, develop, fabricate, and test a frequency-stepped radar system prototype that has the capability to detect and locate buried nonmetallic mines, both antivehicular and antipersonnel, and can be integrated into a man-portable mine detection system testhed.CRC's prototype mine detection radar design is physically contained in two subsystems as illustrated in Figure 1 . The first subsystem is a hand-held scanning wand that contains the antennas for the radar. The second subsystem contains the RF, analog, and digital processing electronics. A display and audio output is incorporated into the first subsystem for operating and ...