Research On Xining Surface Deformation Monitoring Based On Time Series InSAR Technolog

Surface deformation monitoring is of great significance in discovering ground safety hazards and avoiding geological disasters.Compared with traditional surface monitoring methods,synthetic aperture radar interferometry(InSAR)technology is widely used in large-scale surface deformation monitoring due to its advantages of low monitoring cost,wide monitoring range,high monitoring accuracy and non-contact.In this paper,taking Xining city as the research area and selecting 73 scenes descending Sentinel-1A data with a time span from January 7,2018 to June 13,2020.The atmospheric correction is processed using GACOS data,elevation phase correlation model and their combination.Three evaluation indicators including phase standard deviation,elevation phase correlation coefficient and spatial decorrelation distance are used to evaluate the above three correction methods.The annual average deformation velocity of Xining is obtained based on Stacking InSAR technology.Surface time series deformation of Xining is obtained by robust estimation method.The accuracy of the results is verified by simulation experiment and GNSS data.Analyzing the surface deformation situation in Xining.The main conclusions of the paper are as follows:(1)After atmospheric correction using GACOS method,elevation phase correlation method and their combination,the mean improvement rates of interferogram phase standard deviation are 14.44%,23.68% and 21.99% respectively,the mean improvement rates of elevation phase correlation coefficient are 21.23%,87.13% and 88.02% respectively,the mean improvement rates of spatial decorrelation distance are 54.10%,61.48% and 61.48%respectively.It indicates that the elevation phase correlation method and the combination method can more effectively remove the atmospheric delay error than the GACOS method in Xining area.(2)The annual average deformation velocity of Xining is obtained based on Stacking InSAR technology.The results show that the deformation velocity in the main urban area of Xining City ranges from-5mm/a to 5mm/a which is relatively small.It indicates that the main urban area is in a stable state.However,there are five relatively obvious deformation areas in the surrounding mountainous areas with maximum deformation rates of-54.7mm/a,-73.0mm/a,-59.9mm/a,-57.1mm/a,and-58.6mm/a respectively.It shows that there is a potential risk of landslides geological disasters which need close attention.(3)Simulation experiment demonstrates that compared to the least squares estimation model,the robust estimation model has higher stability and use robust estimation method can effectively avoid the influence of some interferograms phase unwrapping error in time series InSAR analysis on the time series deformation results.The time series surface deformation results in Xining city are obtained by robust estimation method.The monitoring results are compared with the GNSS data of 23 observation stations over the same period,and the mean of root mean square error is 6.77 mm,indicating that the time series deformation results with high accuracy can be obtained based on the robust estimation method.The InSAR time series deformation monitoring results show that the magnitude and range of deformation in the five deformation regions are continuously increasing.However,the deformation rates in regions B,C,D,and E are stable and there is an accelerating trend of deformation in region A which deserves particularly close attention.