Mapping and interpreting of subsidence in West Tianjin with high spatiotemporal x-band persistent scatterer SAR interferometry

Ground subsidence in West Tianjin area is explored by means of the persistent scatterer (PS) networking interferometric synthetic aperture radar (PSNInSAR) technique. The pivotal algorithm of the PSNInSAR is briefly represented and the computation is based on 15 high spatiotemporal resolution (HSTR) TerraSAR-X (TX) SAR images acquired between Mar., 2009 and Jan., 2010. The PS subsidence velocity map shows the maximum subsidence velocity as high as 56 to 68 mm/yr, implying that the study area is an active zone for ground deformation. The hydrogeological conditions in the area are examined to explore the mechanism of the uneven subsidence caused by excessive exploitation of groundwater. The derived subsidence measurements are validated with the in situ data taken by the optical leveling at 9 benchmarks, which implies the HSTR PSNInSAR with short radar wavelength (3.1 cm for TX) can reach an accuracy of millimeter (±4.09 mm/yr in our work). The results demonstrate that the HSTR PSNInSAR is of great advantage to detect subsidence and can help to reveal the spatial evolution of the subsidence phenomenon. Advisably, based on the results above and the chief parameters of the radar sensor, the predominance and limitations of the high spatiotemporal TX SAR interferometry in subsidence detecting are discussed.