Monitoring a tunneling in an urbanized area with Terrasar-X interferometry — Surface deformation measurements and atmospheric error treatment

We present results from a deformation monitoring to demonstrate potential and limitations of TerraSAR-X interferometry to measure vertical displacements due to the tunneling of main sewerage pipes along the river Emscher in Germany. In spite of higher sensitivity for deformation gradients the potential for deformation monitoring benefits from high spatial and temporal resolution of the TerraSAR-X data. We analyzed a large stack of TerraSAR-X stripmap scenes to derive regional pattern of vertical displacements with differential SAR Interferometry and small-scale displacements and deformation of objects (infrastructure and houses) in time series of SAR-scenes with Persistent Scatterer Interferometry (PSI). First results from PSI are promising with a great number of detected PS. We show deformation measurements with Artificial Corner Reflectors. Short-time interferograms (11 or 22 days) show high coherence for large areas and therefore are likely less infected by unwrapping errors. Atmospheric errors are important for X-Band SAR. Expected deformation in our application is in the range of mm to cm, similar to tropospheric delay features in their spatial and temporal extent. The atmospheric phase screen in PSI and stacking procedures are smoothing the nonuniform deformation history of progressing tunneling.