Application of the Holographic Radar RASCAN to Cultural Heritage Inspection

This paper explores the application of a holographic radar for cultural heritage investigations. The application is demonstrated with the analysis of a decorative marble plate on the floor of Temple of San Biagio in Montepulciano. RASCAN is the brand name of an holographic subsurface radar that has been developed for landmine detection and construction buildings sounding [NATO Project CBP.NR.NRCLG.982520] and here is used for the first time for the survey of a supposed burial place underneath a marble stone. The radar operates in the band of 3.6-4.0 GHz. This radar is small and is operated by hand scanning, see Fig. 1. The radar images of the marble medallion, obtained by two antenna polarizations, reveal a complex structure of the medallion, the origin of which is not clear without additional information. With our experiments we have tried to interpret to the best the radar images, with the help of an accurate relief and historical information. Fig.1. Process of medallion scanning by Rascan-4 subsurface holographic radar Fig.2. Metric comparison of optical image (on the left) with a holographic radar image (on the right). The spatial correlation between the optical and the Rascan image (see Fig. 2) is very high, as overlapping of two images pointed out. With certainty we can affirm that the contrast obtained in the radar image has dielectric nature and non-metallic, and we can do some hypothesis for interpretation of three contrast patterns enclosed by yellow boxes. Vertical contrast patterns 1 and 2 are the presence of two rows of bricks or wooden bars sustaining the marble medallion. Contrast pattern (#3) is visible in the optical image as a colour change on the marble and could be explained by the presence of humidity or another wooden or brick elements sustaining the medallion. According to an historical investigation we found about the medallion, the presence of Vincenzo Cervini’s burial is quite sure. So we can formulate a reasonable assumption that results from the combination of Rascan image and small historical research. Probably under the marble stone there is an empty area with some bricks to support the medallion. These elements can lie on top of a curved surface of the roof of the burial place. Thanks to the high spatial resolution of this type of radar the signal phase detection of the multiple frequency continuous waves, it is possible to detect subtle features in the image, like reflections from curved surfaces or small change of dielectric properties of materials.