| Tianjin is one of the most serious inland cities in China in terms of land subsidence,which was first discovered in 1923,and the maximum cumulative land subsidence has exceeded 3.4 meters since then.After a long period of treatment,land subsidence in Tianjin has been controlled to a certain extent,but the situation is still severe.Therefore,it is of great social benefit and research value to carry out the necessary research on ground settlement and safety analysis and disaster warning based on the deformation information of monitoring targets to avoid or mitigate the damage caused by potential geological disasters.Interferometry synthetic aperture radar(InSAR)is an all-weather,all-weather technique that can effectively monitor the state of land subsidence and spatial and temporal evolution characteristics.In this paper,using SBAS-InSAR technique,the 44-field Sentinel-1A image data of Tianjin region from 2015 to 2020 are processed,the rate of land sedimentation deformation and cumulative sedimentation volume in Tianjin region are extracted,and the main features of the temporal and spatial evolution of the sedimentation characteristics of the region are analyzed based on the time-series land sedimentation monitoring results of Tianjin region.The main research content and results are as follows.(1)The background of the development of surface settlement in Tianjin is introduced,the basic principles and data processing procedures of InSAR,D-InSAR and time series InSAR techniques are described in detail,and the advantages and applications of PS-InSAR and SBAS-InSAR techniques are analyzed.(2)The most recent results of land sedimentation monitoring in Tianjin are available only until 2019,and the time span is short.Therefore,this paper uses the latest Sentinel-1A image data for 2020 to analyze the long time series from 2015 to 2020 in Tianjin.In this paper,we use the image data from July 2015 to April 2020 covering the Tianjin area in 44 scenes IW mode,and the total data processing results reach 1.3 TB.in order to avoid the effect of temporal and spatial decoherence,the experimental data from 2015 to 2020 are divided into three time periods for processing and analysis: 2015?2017,2016?2018,and 2018?2020.The land deformation fields in the Tianjin area were extracted from the results of the study.Among them,a total of 4901899 coherent target points were identified in the 2015-2017 deformation field,5418898 coherent target points were identified in the 2016-2018 deformation field,and 10936938 coherent target points were identified in the 2018-2020 deformation field.(3)Monitoring of land subsidence in Tianjin area based on Sentinel-1A time series analysis method with SBAS-InSAR.The monitoring results show that there are obvious settlement funnels in Tianjin area,mainly in the towns of Wangqingtuo and Shengfang,with a settlement deformation rate of-136.2mm/a and a maximum cumulative settlement of-346.3mm within the study period.The correlation coefficient between the two reached r to0.89 and the root mean square error was 4.84mm/a,which verified the accuracy and reliability of monitoring the ground settlement by SBAS-InSAR technology.(4)Through the analysis of rainfall,groundwater resource extraction,spatial location distribution of industrial zones and rail traffic from 2015 to 2020 combined with SBAS-InSAR inversion results,over-extraction of groundwater resources is the main cause of land subsidence in the area.Therefore,strict control of groundwater extraction is the main way to mitigate land sedimentation monitoring. |
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