Monitoring of Urmia Lake Bridge Subsidence during 2014- 2021 Using DInSAR-SBAS Method and GPS Data

The Differential Interferometric Synthetic Aperture Radar (DInSAR) can be considered an efficient and cost-effective method for monitoring ground subsidence because of its extensive spatial coverage and high precision. Because of orderly observations from a broad-range product, the new commissioning of the first Sentinel-1 satellite offers better support to operational scrutinies via DInSAR. In the present paper, the results of a Small Baseline Subset Interferometric Synthetic Aperture Radar (SBAS-InSAR) time-series analysis of 42 Interferometric Wide swath (IW) products of Urmia Lake Bridge in northwestern Iran acquired between November 2014 to April 2021 for both descending and ascending pass using the Sentinel-1A observation with Progressive Scans in azimuth (TOPS) imaging mode is studied. The SBAS processing was based upon the analysis of 111 small-baseline differential interferograms. The results demonstrate that the majority of regional ground subsidence rates in the research area ranged from 10 to 210 mm during the study period. Also, the maximum subsidence rate exceeded 210 mm/year. The Line of Sight (LOS) direction for descending pass is 91 mm/year for ascending the pass. The board view displays that ground subsidence is intense on the bridge. The largest subsidence center is located at the central points of the bridge. GPS data verified the SBAS-InSAR-derived result. The results include displacement in the horizontal and vertical directions for ascending and descending passes.