Time Series InSAR Subsidence Monitoring And Tropospheric Delay Correction In Beijing

Land subsidence is a major regional environmental geological hazard in the North China Plain in China.Beijing is an important city in the North China Plain.Land subsidence has been discovered in the area since the 1960 s.In recent years,with the rapid economic development,rapid population growth,rapid increase in groundwater extraction and the expansion of urban engineering construction,which makes the problem of land subsidence in Beijing area increasingly serious,and it is of great practical significance to carry out deformation monitoring.Traditional deformation measurement methods are expensive and difficult to perform large-scale long-term monitoring.The Differential Interferometric Synthetic Aperture Radar(D-InSAR)technique developed from Interferometric synthetic aperture radar(InSAR)and the time-series InSAR technique can effectively compensate for the shortcomings of the traditional measurement methods and have been widely used for surface settlement monitoring in recent years.The core research content and findings of this paper are as follows:(1)Using Envisat-ASAR data from June 2003 to September 2010 and Sentinel-1 data from October 2014 to October 2020,the SBAS-InSAR technique was used to obtain the subsidence distribution in the Beijing area during the two phases and to explore the ground subsidence condition in the area.The results show that during this period,the Beijing area experienced a situation where the subsidence accelerated and then decelerated.The subsidence situation became more serious before 2017,but the subsidence began to slow down after 2017.The maximum subsidence rate rose from-90 to-178 and then dropped to-100mm/yr.The settlement area and rate of settlement in the northern and eastern regions have been greatly improved.Geological conditions,population size,land use type,and the use of water resources are closely related to land subsidence: faults dominate part of the subsidence boundary;the greater the thickness of the compressible layer,the greater the probability and magnitude of deformation;subsidence at the site occurs mainly in densely populated areas;artificial ground is more prone to large-scale subsidence;the restoration of groundwater depth and the reduction of groundwater extraction have slowed the development of ground subsidence in this area.(2)For roads and subways in the area,similar to the overall settlement situation,settlements mainly occur in the eastern and northern settlement areas.For airports,the settlement rate in the northwest of Beijing Capital International Airport is greater than that in the southeast.Runway 2 and Terminal T2 have the most serious uneven settlement;Beijing Daxing International Airport is relatively stable overall,but settlements have been found in the airport expressway in the north and some on-site facilities,which should be followed up with continuous attention.The above three types of large-scale public infrastructure have all started to improve in 2017,some areas begin to stabilize after 2018.(3)In addition,the article also studies the InSAR tropospheric delay error.Four typical process delay correction methods,phase-elevation ratio(Linear),GPS zenith delay correction(GPS-ZTD),GACOS,and ERA5,are evaluated in combination with related indicators.The results show that the comprehensive applicability of GACOS in the test area is better than the other three.But up to now,there is no correction method that can better estimate and remove the tropospheric delay error,which can be combined with multiple means for joint as well as iterative estimation.