Spatio-temporal InSAR for bridge monitoring: Integrating physics-based models with persistent scatterer interferometry

This work presents a novel spatio-temporal InSAR (ST-InSAR) framework that integrates physics-based structural models into persistent scatterer interferometry (PSI) for bridge monitoring. The proposed approach mitigates the limitations of conventional PSI in civil infrastructure applications, namely large displacements that exceed the ambiguity limits, and absence of correlation with air temperature. ST-InSAR exploits spatial correlation among PSs to jointly estimate the displacements across the entire structure. The framework is applied to the Colle Isarco Viaduct (Italy), where its performance is compared with conventional multitemporal PSI, using benchmark topographic measurements. Results show that ST-InSAR detects structural displacements with an accuracy on the order of 2 mm, even where PSI fails. Additionally, temporal coherence increases from approximately 0.08 (PSI) to over 0.9. Finally, the framework enables the estimation of the temperature gradient across the bridge deck with an accuracy better than 1°C, providing information about the structural thermal state beyond displacement monitoring.