Identification and removal of above‐ground spurious signals in GPR archaeological prospecting

Ground‐penetrating radar (GPR) is a shallow geophysical method increasingly used in archaeological prospecting to detect buried remains and to map the stratigraphy of the uppermost earth layers embodying the archaeological features. The GPR sections, however, can be contaminated by spurious correlated signals caused by above‐ground obstacles (buildings, trees, fences, power lines) placed either in‐line or off‐line with respect to the profile (surface scattering). In the case study presented this problem is analysed for a 35 MHz GPR survey carried out for stratigraphical purposes in the archaeological site of the Roman Ships near Pisa (Italy). The investigation inside the archaeological excavation, when the level was about 5 m below the ground surface, produced a severe surface scattering problem caused by the iron sheet‐piling protecting the excavation walls and bordering some of the partly excavated boats. An attempt to interpret the profiles was carried out in a zone where the relatively simple geometry of the metallic enclosure allowed understanding of the possible origin of spurious events, also thanks to the high density of profiles acquired along two orthogonal directions. Migration at the air velocity and geometrical considerations helped the identification of hyperbolic and slightly slanted features as surface scattering phenomena from different sides of the iron sheet‐piling. A simple but original subtraction procedure was successful for the attenuation of some of the spurious reflections. After this partial removal, other spurious signals could be recognized more easily as well as two weak subhorizontal reflections of probable stratigraphical meaning. Subsequently, filtering procedures based on f‐k and Radon transform methods were tried to further reduce the spurious signals, thus enhancing the visibility of the interesting reflections. Copyright © 2005 John Wiley & Sons, Ltd.