Advanced Coregistration Methods Of Sentinel-1 A/B Satelliates And Its Application In Tianjin Area

As a new geodetic technology,Interferometric Synthetic Aperture Radar(InSAR)has been widely used in surface deformation monitoring.In order to overcome the constraints of temporal and saptial decorrelation effect and atmospheric delay of long-time deformation monitoring,and improve the applicability of InSAR technology,time series InSAR has been proposed.Although it is possible to overcome phase decorrelation and atmospheric delay effects,there still some difficulties and problems.Complex image registration is the most important and necessary step in the processing of InSAR interferometric data processing.Due to the fast change of Doppler center in the azimuth direction of Sentinel-1 TOPS(Terrain Observation by Progressive Scans)images,phase jump will occur between different Bursts while the registration accuracy could no reached 0.001 pixels in azimuth direction during interferometric processing.Generally,the TOPS Image Sentinel-1 satellite usually uses Enhanced Spectral Diversity(ESD)of overlapping regions between bursts to achieve high accuracy registration based on geometric registration.Because the accuracy of Enhanced Spectral Diversity is affected by the factors such as the incoherent noise,the following improvements for Sentinel-1 image registration are proposed to ensure the accuracy of image registration:(1)The ESD phase-based non-weighted periodogram estimation is upgraded to a weighted periodogram estimation;Generally,the residual offset of geometric registration always estimated by Periodogram Method,however,due to the different noise level of each pixel,each phase observation values have been weighted in this paper.The results indicate that the weighted periodogram method could get better resutls than equal weighted periodogram method.In addition,with less sample size,the estimation results of these two methods could get greater difference,and the weighted periodogram method could represent more obvious advantages.(2)The range overlap area is used to increase the observation amount of ESD.The experiment results show that the accuracy of the forward ESD method is low,so,in this paper backward ESD method and ESD in the direction of azimuth have been combined to improve the accuracy.Especially,this method could make up for the shortage of azimuth ESD observations when the overlap area with low coherence.(3)In order to achieve further optimization of the direct registration results,combined adjustment is proposed to process the ESD redundant observations which are combined from the image interferogram pairs after the direct registration.With large number of Bursts,the trend of residual offect is difficult to fit by ploynomial,as a result,direct registration is difficult to meet the needs of long strip and large area.In this paper,combined adjustment is proposed to process the ESD redundant observations which are combined from the image interferogram pairs after the direct registration.In order to avoid the estimation caused by ill-conditioned covariance matrix,the correlation between image interference pairs have not been taken into considetation.The results indicate that joint registration can further improve the accuracy of registration.(4)In this study,we employed multitemporal InSAR(Interferometric Synthetic Aperture Radar)(MT-InSAR)to detect spatial and temporal ground deformations over the whole Tianjin region in the North China Plain area.Twenty-five ascending Sentinel-1A terrain observation by progressive scans(TOPS)synthetic aperture radar(SAR)scenes covering this area,acquired from 9 January 2016 to 8 June 2017,were processed using InSAR time series analysis.The deformation results derived from Sentinel-1A MT-InSAR were validated with continuously operating reference stations(CORS)at four sites and four stations of the Crustal Movement Observation Network of China(CMONOC).The overall results show good agreement,demonstrating the suitability of applying Doris with Sentinel-1A data to high-resolution monitoring of surface deformation.Significant deformation variations have been observed in different parts of Tianjin.These gradually increased from the central part of the metropolitan area to the nearby suburbs.The deformation rate of the main urban area is well-balanced and it is also relatively linear,with uplifting rates ranging from 0 to 20 mm/yr.However,due to the diversity of the geological conditions and anthropogenic activities,remarkable signs of subsidence were found in several parts of Tianjin.In particular,the south-western part of Wuqing District and western part of Beichen District showed subsidence rates of up to-136 mm/yr.We also found that,in addition to groundwater over-exploitation and lithological characteristics,additional factors also influence ground subsidence,including dynamic loads(e.g.,railways),static loads(e.g.,urban construction),and groundwater recharging.