Key Points in InSAR Process to Measure Surface Deformation in Cangzhou

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 studied first. According to the 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. Filtering can deal with the noise caused by low coherence to some extent. The outcome unwrapped phase maps are geocoded and translated into deformation values. And 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 subsidences 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, and is expected to be applied in surface deformation induced by groundwater, gas, oil pumping and etc.