Key Steps in InSAR Process to Measure Surface Deformation in Cangzhou
Lixia Gong(1) , Jingfa Zhang(1)
, Qingshi Guo(2)
, and Wenliang Jiang(1)
Institute of Crustal Dynamics, CEA,
Postbox 2855, Beijing,
(2) Heibei Remote Sensing Center, Huaizhong Rd, Shijiazhuang, 050051,Shijiangzhuang, China
InSAR technology is applied to measuring surface deformation caused by groundwater extraction in this Paper. ERS1/2 and JERS-1 SAR data are both considered. Firstly, characters of Cangzhou city and the subsidence are summarized as the following; 1) the vast farmlands complicate InSAR process, 2) the subsidence rate here is very large, 3) the test area is very flat, and 4) accurate DEM is already available. According to the above characters, appropriate processing methods are designed for this experiment. 2-pass instead of 3-pass differential method is chosen. JERS1 SAR images are used instead of ERS ones because their better tolerance of vegetation and large deformation. A set of late processes are also designed to improve the interferograms and to extract proper subsidence from the unwrapped phase. The outcome unwrapped phase maps are geocoded and translated into deformation values. Then discontinuities in unwrapped phase due to very low coherence are masked. Finally a density slice is applied to get pseudo-color subsidence maps for better visualization. Several SAR pairs are processed and subsidence maps of different period are obtained. Deformation pattern in Cangzhou is analyzed from the subsidence maps and the further extracted profiles. Extension and quantity of InSAR measurements are compared with the actual subsidence values. InSAR technology proves to be an efficient way to measure land subsidence.