Combined in-situ and Persistent Scatterers Interferometry Synthetic Aperture Radar (PSInSAR) monitoring of land surface deformation in urban environments - case study: tunnelling works in Bucharest (Romania)

Abstract

ABSTRACT Monitoring land surface deformation is one of the most reliable approaches that can be used to study, manage and forecast several geohazards (such as subsidence, landslide, sinkholes, etc.) linked to either natural or anthropogenic driving forces. The importance of such tools becomes more visible in urban environments where hazards would have aggravated consequences. Within this framework, a combined in-situ and remote sensing monitoring approach, that can be used to support a physically based assessment of land surface deformations driven by subsurface perturbations in urban environments, is presented. The approach makes use of multidisciplinary interferometric-hydrogeological-geotechnical investigation techniques. The present study was conducted on a test site in Bucharest where the effects of subway tunnelling and associated dewatering works were investigated. A referencing network specifically designed to support the targeted physically based assessment was implemented in this area. The system consisted of a set of monitoring stations equipped with corner reflectors, inclinometric and piezometric tubes, and levelling benchmarks. This system was deployed for a one year long monitoring campaign of in-situ surveying (of groundwater level, land surface vertical deformation (topographical levelling) and vertical profiles with horizontal displacements in soil (inclinometer surveys)) and remote sensing surveying (X-band Synthetic Aperture Radar (SAR) images were acquired). The obtained in-situ measurements (horizontal and vertical surface deformations) were used to cross-reference remotely sensed (obtained using Persistent Scatterers Interferometry technique) temporal deformation (along the line of sight) profiles. The results show that even though the investigated tunnelling and dewatering works did not produce detectable surface deformations, the SAR displacement trends fitted the in-situ measurements within a root mean square error of 1.5 to 4.8 mm, and thus the remote sensing approach proved again to be a reliable alternative to in-situ measurements for an adequate assessment of land surface deformation in urban and potentially non-urban environments.