Differential settlements monitoring in railway transition zones using satellite-based remote sensing techniques

Railway track transitions are prone to uneven settlements and track geometry degradation. Traditional monitoring methods are limited in coverage, which highlights the need for novel solutions. This study proposes a method that systematically integrates the high spatial resolution of Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) with the broader coverage of Small Baseline Subset (SBAS). A correction method for abnormal InSAR time series is developed, considering both consecutive phase unwrapping errors as well as outlier displacements. Model parameters are optimized through Monte Carlo analysis embedded with grid search. The proposed PS-SBAS InSAR processing method is applied to generate the track longitudinal profile of a railway transition section and is compared with track inspection data. The results show: (1) the hybrid PS-SBAS approach provides higher resolution and robustness for tracking long-term differential settlement along railway tracks. (2) There is a strong correlation between track longitudinal level and the InSAR-derived profile in the bridge approaches with high differential settlement rates. (3) InSAR can serve as a complementary method to traditional inspections, capturing the progression of differential settlement and enhancing the understanding of long-term settlement patterns and their impact on track performance.