The effect of the elevation of GPR antennas on data quality

In many GPR-measurement situations it is possible to measure with the antennas of the GPR-system in contact with medium containing the unknown objects. In this paper, we have tested the performance of a commercial Pulse Ekko 1000 system at various heights above a sand-surface. We show measurements over the same area with the antennas of this near-surface GPR system at four different heights above the surface. We show that the decrease in signal to noise ratio is small for two-way distances between antenna and surface is smaller than one third of the dominant wavelength. For larger distances, the signal quality decreases rapidly for data processing purposes and object detectability.