Application of 3D visualization techniques in the analysis of GPR data for archaeology

In this work, some results of a GPR survey carried out in a 10 000 m2 large archaeological site, located in Lecce (Italy) near to a necropolis dating from the Messapian to the Roman imperial age, are reported. After a preliminary survey, performed on the entire area along parallel 1 m spaced profiles using a 200 MHz and a 500 MHz antenna in single-fold continuous mode, some smaller areas were selected, where the survey was repeated decreasing the profile spacing down to 0.50 m for the lower frequency antenna and to 0.25 m for the higher one. For two selected zones (D and B) the processed data were visualized in 3D space not only by the standard time slice technique, but also by two recently proposed approaches, namely by iso-amplitude surfaces of the complex trace amplitude and by 3D projection of energy and envelope stacks. The immediacy in revealing the spatial positioning of highly reflecting bodies, such as the anomaly interpreted as an old refilled cistern in zone D, makes 3D visualization techniques very attractive in archaeological applications of GPR. Their sensitivity to the signal/noise ratio is, on the other hand, highlighted by the quite poor performance in zone B, where the only reliable result provided by all the techniques was the soil/bedrock reflection, whereas none of them could effectively enhance the visibility of weak dipping reflections noted on 2D sections and probably related to fractures or bedding planes in the calcarenitic basement. The performance of the various techniques in these two different situations allowed insights into their main advantages and drawbacks to be gained.