Shanghai subway tunnels and highways monitoring through Cosmo-SkyMed Persistent Scatterers

Synthetic Aperture Radar Interferometry (InSAR) is an alternative technique to obtain measurements of surface displacement providing better spatial resolution and comparable accuracy at an extremely lower cost per area than conventional surveying methods. InSAR is becoming more and more popular in monitoring urban deformations, however, the technique requires advanced tools and high level competence to be successfully applied. In this paper we report important results obtained by analyzing new high resolution SAR data in the Shanghai urban area. The data used in this work have been acquired by the Italian X-band sensor Cosmo-SkyMed. About 1.2 million of individual and independent targets have been detected in 600 sq km, revealing impressive details of the ground surface deformation. Using the SARPROZ InSAR tool and integrating the results with Google Earth, we were able to track subway tunnels recently excavated and several highways. Tunnels are visible due to very localized subsidence of the above surface along their path. On the other hand, highways, standing over the ground, in most cases show higher stability than the surrounding areas. The density of targets is so high to allow studying the profile of the tunnel subsidence, which is very useful to predict building damage. Finally, the identification of targets on high buildings helps checking the stability of high constructions along the subway lines, highlighting possible risky situations.