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Ground Penetrating Radar (GPR) systems fall into the category of ultra-wideband (UWB) devices. Most GPR equipment covers a frequency range between an octave and a decade by using short-time pulses. Each signal recorded by a GPR gathers a temporal log of attenuated and distorted versions of these pulses (due to the effect of the propagation medium) plus possible electromagnetic interferences and noise. In order to make a good interpretation of this data and extract the most possible information during processing, a deep knowledge of the wavelet emitted by the antennas is essential. Moreover, some advanced processing techniques require specific knowledge of this signal to obtain satisfactory results. In this work, we carried out a series of tests in order to determine the source wavelet emitted by a ground-coupled antenna with a 500 MHz central frequency.

This article presents the characterization of a mediaeval bridge located in Fillaboa, Galicia (northern Spain). The study of this bridge involves data acquisition about the structure (geometry, visual inspection of damages, and nondestructive testing), the evaluation of the possible damage mechanisms compatible with the observed cracks and fissures, and the dynamic evaluation of the structure. This bridge is a masonry four-lancet arches bridge, with damage on the piers and abutments. Two non-invasive methodologies are applied to obtain information about the bridge: ground-penetrating radar (GPR) survey and ambient vibration noise measurements. The drawings of the structure were created using close-range photogrammetry (CRP). A finite elements model of the structure was obtained prior to the vibration field measurements, as a preliminary evaluation. Data obtained from GPR and the geometry determined with CRP were the information used in this preliminary model of the bridge. This model was improved using the dynamic field test to compare model behavior and to validate the numerical results. A second and more accurate model was then obtained by using finite elements according to the experimentally measured modal frequencies (the possible first three transversal vibration modes of the bridge).