SBAS-InSAR time series ground subsidence monitoring along Metro Line 13 in Qingdao, China

The improved metro in Qingdao is an important means of transportation. Accurate measurements and detailed analysis of ground subsidence along the metro lines are critical. This study, for the first time, used the small baseline subset interferometric synthetic aperture radar (SBAS-InSAR) technique to monitor and analyze the spatiotemporal distribution and evolution of ground subsidence along the metro lines. Twenty-seven SAR images were processed to obtain ground subsidence information along Qingdao Metro Line 13 (Jialingjiang road station–Jimiya station) from January 2018 to December 2019. The uneven ground subsidence for each section of the line and spatiotemporal evolution of the subsidence trough in the transverse direction were analyzed using the entropy method and Peck’s formula. The ground subsidence monitored by SBAS-InSAR was verified through field investigation and leveling-monitored results. Most sections along Metro Line 13 were stable; ground subsidence zones were concentrated at the right turn of “Jialingjiang road station–Xiangjiang road station” and the junction of Jinggangshan road and Lijiang West road. This was caused by tunnel excavation and construction of a metro station and nearby high-rise buildings. The SBAS-InSAR- and leveling-monitored results were consistent with a maximum absolute difference of 3 mm and root mean square error of ± 2 mm. SBAS-InSAR accurately determined the location and distribution of ground subsidence along the metro line and in surrounding areas, providing support for construction, operation, and maintenance of the metro. This study furthers the application of SBAS-InSAR for ground subsidence monitoring along urban roads and metro lines.