Gated stepped-frequency ground penetrating radar

This paper describes a newly developed stepped-frequency ground penetrating radar (SFGPR) prototype operating across the 10-620 MHz frequency band. The SFGPR system has been developed to improve the maximum penetration depth capability of ground penetrating radar (GPR) applications without degradation of resolving power. The radar has the unique capability to employ a short gate at each frequency step that can suppress unwanted strong signals relative to weak reflections from deep targets. The system performance is approximately 175 dB in ungated mode and 170 dB in gated mode, with reference to a 10 ms integration time and a 10 dB signal-to-noise ratio. The current system is suitable for operation in a vehicle and incorporates a real time display similar to conventional impulse GPR. It is capable of recording 50 depth profiles per second. Subsurface images obtained with the gated SFGPR of a perched water table on a sand island, a culvert in high-loss ground, and a 500 lb bomb buried at 1.7 m deep are presented. A frequency compensation procedure is used to improve image clarity. The weakest confirmed underground target has a signal power 100 dB down on the transmitted power. Such a signal would be near the noise floor of a commercial impulse GPR. (C) 2000 Elsevier Science B.V. All rights reserved.