Research And Application Of Time Series InSAR Based On Atmospheric Delay Correction By PS Points In Urban Land Settlement Monitoring

Land subsidence is a geological phenomenon caused by natural factors or human factors to consolidate and compress underground loose rock layers and reduce the elevation of ground in a certain area.It has the characteristics of wide coverage and great destructiveness,and is one of serious disasters that threatens people's lives and property.The urban area and its suburban areas are economically developed and densely populated.Once land subsidence occurs,it will cause serious losses.Therefore,urban land subsidence monitoring is of great significance to urban development and people's lives.Traditional land subsidence monitoring methods,such as leveling,gravity measurement,groundwater level monitoring,GPS monitoring,etc,cannot meet the requirements of ground subsidence monitoring in terms of cost,spatial resolution and period.In the past ten years,Synthetic Aperture Radar Interferometry(InSAR)has great advantages in the field of measuring surface microdeformation due to its wide coverage,low cost,high spatial resolution,high time resolution and all-weather.Therefore,it has become a research hotspot of many experts and scholars in geodesy and other related fields.Atmospheric delay is one of the serious interference factors that restrict the measurement of surface deformation by InSAR technology.Although,compared to Difference Synthetic Aperture Radar Interferometry(D-InSAR)technology,the time-space filtering method of Time Series InSAR technology greatly weakens the atmospheric delay effect.However,time-space filtering does not diminish the vertical stratification delay effect of the atmosphere.Therefore,in order to improve the atmospheric delay correction effect of Time Series InSAR technology,this paper optimizes the selection method of Permanent Scatterer(PS)and optimizes the atmospheric vertical layered delay model based on the PS points observation elevation value.The main research contents and results of this paper are as follows:(1)Studying the role of Permanent Scatterer technology in Time Series InSAR technology in atmospheric delay correction,and optimizing the PS selection method—coherence coefficient and amplitude dispersion double threshold method and phase selection analysis based PS selection method are proposed.Combined,the experimental comparison proves that the optimization method improves the reliability of PS points selection.(2)Based on the optimized PS points,the PS points elevation information is introduced into the linear model of atmospheric vertical stratification delay to estimate the model parameters.The robustness of the parameter estimation is illustrated by the terrain elevationinterference phase relationship diagram.Then,remove the vertical stratification effect of the atmosphere before using the space-time filtering method.The effectiveness of the method in atmospheric delay correction is proved by comparing the interference phase diagram before and after the atmospheric delay correction.(3)Taking Wuhan as a research area and total of 25 Sentinel-1A images from March 2017 to January 2018 as the main data source.Based on the above PS optimization selection method and linear model parameter optimization estimation method,land subsidence in urban and suburban areas of Wuhan was analyzed.The subsidence results show that the annual average sedimentation rate of the study area is less than 5.5 mm and overall sedimentation is not obvious.