Metal-sheet test to estimate shape and frequency content of the radar pulse

Appropriate GPR data processing and inversion require a reliable estimation of the radar pulse. In particular the knowledge of the shape and frequency content of the wavelet sent into the ground is an important issue not only for processing an interpreting reflection profilles, but also for GPR tomography, especially for amplitude tomography. Common practice considers the nominal antenna frequency as a measure of the bandwidth of the radar wavelet in the air, which in turn is assumed to be equal to the peak (dominant) frequency. Raising the antenna above a totally-reflecting metallic slab is the simplest way to gain information on the shape of the radar pulse in the air. This is the experimental calibration method generally used for correcting zero-time drift and to obtain a reference signal for amplitude analysis. This method was applied in this study to extract information on the frequency content of the emitted radar wave. Experimental errors related to ambient noise and positioning inaccuracies impose great care for a correct extraction of the needed attributes. The same test was also useful to gain insights into the influence of the filters applied in the acquisition stage.