Comparison of a stepped-frequency continuous wave and a pulsed GPR system

摘要

A new stepped-frequency continuous wave (SFCW) ground-penetrating radar (GPR) system was tested. The GPR uses a special arrangement of different antenna sizes to cover a large frequency bandwidth and to have a very close spacing between the air-coupled antennae, closer to the Nyquist sampling interval in a cross-line direction than is normally possible during conventional field recording. The data processing is described but is more complicated than for a pulsed system and very time-consuming. A new background removal in frequency domain has also been shown to be an alternative. Comparing data from this SFCW and a pulsed system reveals that there is no advantage using frequency domain technology with an air-coupled antenna. The penetration depth is even significantly reduced, and hence the stepped-frequency technology provides only reasonable data in about 20% of the cases where good data are recorded with a time domain system using a ground-coupled antenna, as tested on a wide variety of sites and applications. This can be explained by the bad coupling to the ground and the strong first reflection of the air-coupled antenna.