GNGTS 2016 - Atti del 35° Convegno Nazionale

574 GNGTS 2016 S essione 3.2 Ground Penetrating Radar Imaging Software (Goodman, 2015). The basic radargram signal processing steps included: i) post processing pulse regaining; ii) DC drift removal; iii) data resampling, iv) band pass filtering, v) migration and vi) background filter. With the aim of obtaining a planimetric vision of all possible anomalous bodies the time- slice representation technique was applied using all processed profiles (Goodman et al. , 2008a, 2008b; Goodman and Piro, 2013; Leckebusch, 2008; Piro et al. , 2008, 2012; Utsi 2006). Time- slices are calculated by creating 2-D horizontal contour maps of the averaged absolute value of the wave amplitude from a specified time value across parallel profiles Time slice data sets were generated by spatially averaging the squared wave amplitudes of radar reflections in the horizontal as well as the vertical. The squared amplitudes were averaged horizontally every 0.25 m along the reflection profiles 3 ns (for 400 MHz antenna) and 6 ns (for 70 MHz antenna) time windows (with a 10% overlapping of each slice). The resampled amplitudes were gridded using the inverse distance algorithm with a search radius of 0.75 m. In addition pseudo three-dimensional volumes of the reflections were generated to produce isosurface images. In Fig. 2 the time-slices (in the time windows from 58 to 61 ns twt for 400 MHz antenna) for the investigated area are shown. On this map the individuated anomalies are visible and in particular the reflections obtained in the area N-E to the basilica can be related to the remains of the early Christian bishop’s palace (high medieval period). Fig. 3 shows, the time-slices at the time-window 112-118 ns (for the 70 MHz antenna) obtained in the same area. Ground Penetrating Radar (GPR) survey at the Lateran has produced significant and fruitful results. The use of two different antennae has enabled to reach depths of up to 6÷7 m. All the obtained results are presented in 3D animation using real time Open GL graphic displays in which isosurface rendering, 3D time slice fence diagram are mixed with the filtered radargrams. Acknowledgements. The Authors are very grateful to Maria Ida Moretti and Daniele Verrecchia for their fruitful collaboration during the survey, the team of Newcastle University for the topographic support and Authorities of San Giovanni in Laterano Basilica for their help during the survey. References Gaffney V., Piro S., Haynes I., Watters M., Wilkes S., Lobb M., Zamuner D.; 2008: Three-Tier Visualization of San Giovanni in Laterano, Rome, Italy . 12th International Conference on Ground Penetrating Radar, June 16-19, 2008, Birmingham, UK. Proceedings Extanded Abstract Volume. Goodman D., Piro S.; 2008a: Ground Penetrating Radar (GPR) surveys at Aiali (Grosseto) . In “Seeing the Unseen. Geophysics and Landscape Archaeology”. Edited by Campana and Piro. CRC Press, Taylor & Francis Group. Oxon UK, (ISBN 978-0-415-44721-8), pp. 297-302. Goodman D., Piro S., 2013. GPR Remote sensing in Archaeology. Springer (Ed), ISBN 978-3-642-31856-6, ISBN 978-3-642-31857-3 (eBook), DOI 10.1007/978-3-642-31857-3. Springer, Berlin, (Germany).Goodman D.; 2015: GPR-Slice 7.0, Manual. Leckebusch J.; 2008: Semi-automatic feature extraction fromGPR data for archaeology . Near Surface Geophysics,Vol. 6 , N.2, 75-84. Piro S., Goodman D.; 2008: Integrated GPR data processing for archaeological surveys in urban area. The case of Forum (Roma, Italy) . 12th International Conference on Ground Penetrating Radar, June 16-19, 2008, Birmingham, UK. Proceedings Extanded Abstract Volume. Piro S., Campana S.; 2012: GPR investigation in different archaeological sites in Tuscany (Italy). Analysis and comparison of the obtained results . Near Surface Geophysics, 2012 , 10 , pp. 47-56, doi:10.3997/1873- 0604.2011047. Utsi E.; 2006: Improving definition: GPR investigations at Westminster Abbey . Proceedings of 11th International Conference on GPR. Columbus Ohio, USA.