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

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.