Contribution Factor Analysis of the Wuhan Yangtze River Bridge Deformation Using Sentinel-1A SAR Imagery and In Situ Data  
[PERSON]  
1 College of Geomatics and Geoinformation, Guilin University of Technology, Guilin 541004, China;  
[EMAIL_ADDRESS] (C.W.); [EMAIL_ADDRESS] (L.Z.); [EMAIL_ADDRESS] (Z.L.); [EMAIL_ADDRESS] (L.L.); [EMAIL_ADDRESS] (L.L.); [EMAIL_ADDRESS] (L.L.); 111111  
and even visual inspection [7; 8]. However, due to limitations on human and financial costs, such measurements are usually only available at sparse discrete locations or at low time sampling frequencies [9; 10; 11]. Therefore, it is necessary to explore new methods for monitoring bridge deformation.  
Interferometric synthetic aperture radar (InSAR) is a spaceborne geodetic measurement technology that can obtain spatially continuous surface deformation information within a study area in a short period of time [12; 13; 14]. It has the advantages of a large measurement range, no regional constraints and no impact on the normal operation of bridges. It can simultaneously monitor multiple bridges within the same image, therefore it has good application prospects in bridge deformation monitoring [15; 16].  
Many scholars have conducted relevant studies on bridge deformation monitoring using InSAR technology. In 2016, [PERSON] et al. monitored the displacement of Nanjing Dashengguan Yangtze River high-speed railway bridge based on PSInSAR technology and computed the regression models of the longitudinal displacements versus the ambient temperatures. In addition, the thermal expansion of the bridge was analyzed [17]. In 2018, [PERSON] et al. derived the deformation of the Donghai Bridge from January 2009 to July 2009 based on TCPInSAR technology. During the co-registration procedure, only those TCP offsets identified in each of the two SAR acquisitions over the entire observation period were used for the joint alignment, and local Delaunay triangulation was employed to construct point pairs to mitigate atmospheric artifacts. It is concluded that the large deformation rate on the cable-stayed bridge is mainly caused by thermal expansion [18]. [PERSON] et al. present an approach suitable to overcome the high-phase-gradient problem in cases where no DSM is available, in order to enhance the accuracy of the estimated deformation rates. The long and short baseline iteration method was used to extract elevation in PSInSAR data processing, and the linear deformation rate and seasonal deformation of PS were extracted from the InSAR deformation time series, resulting in better accuracy results [19].  
In this paper, the deformation of the Wuhan Yangtze River Bridge in the study period was analyzed and obtained data based on SBAS-InSAR (small baseline subset interferometric synthetic aperture radar) technology, and the results were compared with the bridge structure, human activity, temperature and stratigraphy. SBAS-InSAR technology is proposed to reduce the influence of temporal and spatial decorrelation and atmospheric delay [20]. For deformation monitoring of large span bridges, this method has a higher spatial resolution, the ability to accommodate large variations in the monitoring area, the ability to account for atmospheric effects, and the ability to perform reliable time series analysis. Large-span railway bridges provide stable and smooth passage for trains, which is the key to ensuring good economic and social benefits for railroads. The deformation analysis of the Wuhan Yangtze River Bridge contributes to the safety control of such large-span railway and road bridges [21].