Monitoring land subsidence by PS-DInSAR and SBAS methods in Tianjin city

Because of groundwater over-exploitation, the land subsidence of Tianjin city has become more and more serious. Some researchers tried to use D-InSAR technique to monitor the subsidence of this area. However, D-InSAR has some problems such as space and time baseline decorrelation and atmospheric influence. In order to obtain long time series land deformation with high accuracy, SAR image set to monitor land subsidence has become a research focus. PS-DInSAR (Persistent Scatterers-DInSAR) and SBAS (Small Baseline Sets) are two classical methods to monitor land subsidence by SAR images. The former chooses one image as the master and the latter chooses several images as the masters according to the threshold of baselines. Using eighteen ERS images and SRTM DEM data the land subsidence of Tianjin city from 1992 to 1998 was obtained by two methods mentioned. 18906 and 42041 PS points were identified respectively by PS-DInSAR and SBAS. While, 16.4 mm/a and 24.2 mm/a of the mean maximal subsidence velocities were obtained respectively. Although they are different in values, the distributions and subsidence laws of points are nearly same.