Subway tunnels identification through Cosmo-SkyMed PSInSAR analysis in Shanghai

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 urban areas. Using the SARPROZ InSAR tool and integrating the results with Google Earth, we discovered the (not public) precise tracks of new subways lines in Shanghai by detecting the millimetric surface subsidence caused by tunnel excavation. The data used in this work have been acquired by the Italian sensor Cosmo-SkyMed. About 1.2 million of individual and independent targets have been detected in 600 sqkm, revealing impressive details of the ground surface deformation. Through the high spatial resolution (about 2 m) and millimetric sensitivity in the Line Of Sight (LOS), Cosmo is able to highlight very localized subsidence with remarkable accuracy.