Satellite and on-site monitoring of subsidence for heritage preservation: A critical comparison from Piazza del Duomo in Pisa, Italy

Monitoring of soil displacements is often crucial to the preservation of monumental buildings, since these structures are highly sensitive to differential settlements. Synthetic Aperture Radar (SAR) images from satellites appear as a tempting tool for monitoring, since they can be compared through interferometric techniques to track soil or building displacements in time. But interferometric SAR, which accuracy varies with image quality and type of displacement, has to be validated with on-site measurements. Exploiting the availability of open source data from the European Sentinel-1A and 1B satellites, this study aims at providing practical insight regarding the use of these remote sensing sources and method to monitor the well-being of monumental structures. Piazza del Duomo in Pisa (Italy) is selected as a case study, for its long historic record of on-site measurements and for the special role that settlements play in the behaviour of its monuments. The authors outline the advantages and limitations of the freely available SAR data from Sentinel satellites for the purpose of structural health monitoring of monumental structures, comparing it with information obtained through levelling.