Detecting voids within a historical building facade: A comparative study of three high frequency GPR antenna

Ground penetrating radar is becoming an established component of the stone conservation researcher's arsenal. There is great potential in this quick and non-destructive technique that provides confirmation of deterioration features, such as voids, whose presence has been suggested using other tools. The past application of this technology has focused upon block scale stone deterioration, with less attention given to the study of features that extend across multiple blocks within the walls. The aim of this paper was to primarily to demonstrate the suitability of GPR for identifying void spaces when run across a rough surfaced wall facade. Additionally, this work aims to aid in the application of GPR for this purpose, by providing a comparison of three commonly used antennas to inform equipment choice during survey design. For this study, three high frequency antennas, 1.2 GHz, 1.6 GHz and 2.3 GHz, were run along the same perpendicular test lines across multiple blocks within a historical building facade. The resultant reflection profiles demonstrated that GPR can identify the presence of features within the blocks when run across a rough wall section. However, without the use of additional information from secondary data sources it is not possible to confirm the identity of features. The comparison of the three antennas, showed that the 1.6 GHz antenna was the least suited for this task, due to the presence of extensive ringing in the resultant reflection profiles. Alternatively, the 1.2 GHz antenna is most suitable for investigations deep within the wall and the 2.3 GHz better suits highly detailed analysis of features present within the near surface material. The choice of the most appropriate antenna depends upon the nature of the task it will be deployed for. (C) 2018 Elsevier Masson SAS. All rights reserved.