PSI - Issue 84

Michela Pulsoni et al. / Procedia Structural Integrity 84 (2026) 214–222 M. Pulsoni et al. / Structural Integrity Procedia 00 (2026) 000–000

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1. Introduction The safety and durability of infrastructure increasingly depend on the ability to observe, understand, and manage the structural performance of bridges and viaducts throughout their entire lifetime. The ageing of existing assets, the increase of service loads, and several critical events in recent years pointed out the limits of inspection approaches (Clemente, 2020). In this context, remote sensing technologies are assuming a strategic role in supporting and enhancing traditional inspection and monitoring systems, thanks to their rapid, continuous, non-invasive, and high precision data acquisition capabilities, which enable more timely and better-informed diagnostics. Among remote sensing solutions, the three techniques presented in this article prove most effective for bridge and viaduct monitoring studies: TInRAR (Terrestrial Interferometric Real Aperture Radar), Photomonitoring, and InSAR (Interferometric Synthetic Aperture Radar). TInRAR makes it possible to measure deck deformations at high resolution during load tests and under operational conditions, and to analyse the dynamic response of structures by identifying natural frequencies and modal behaviour. Photomonitoring – through networks of fixed cameras and automated image-analysis algorithms – enables continuous visual control aimed at the early detection of anomalies, surface degradation phenomena, and debris accumulation on piers and abutments. At territorial scale, satellite-based InSAR allows the analysis of slow deformations and differential displacements over wide areas with millimetric precision, leveraging multi-year historical archives and providing spatial and temporal context for the local behaviour of individual structures. Against this backdrop, the present work offers a comparative, multidisciplinary analysis of four real case studies on Italian bridges and viaducts, in which different combinations of remote sensing techniques were employed: • Ponte Margherita and Ponte Amedeo, monitored by means of photo-monitoring and satellite interferometry. • Viadotto Puleto and Viadotto Tevere IV, subjected to static and dynamic monitoring with TInRAR. The goal is to optimize the integrated use of remote sensing techniques for the diagnosis and surveillance of strategic infrastructure, assessing their performance, limitations, and complementarity. The paper also presents a synthesis of operational innovations, best practices, and lessons learned from field experience, with the aim of providing guidance for future applications and for the development of network-scale remote monitoring systems. 2. Methodology 2.1. AD-InSAR Satellite-based Synthetic Aperture Radar (SAR) technology offers a unique complementary capability: providing both historical perspective through archived data dating back approximately 30 years and wide-area coverage that contextualizes individual structures within their broader deformation environment. SAR data provides essential advantages for bridge and viaduct monitoring at multiple scales: • Temporal Scale: Satellite archives provide historical context through missions such as ERS (1991-2000), ENVISAT (2002-2012), and more recent high-resolution missions like Sentinel-1 (2014-present) and COSMO SkyMed (2007-present). This historical record allows to understand the long-term deformation history of structures and their surrounding areas, which is impossible with newly installed ground sensors. • Spatial Scale: Satellite data enables wide-area assessment, allowing simultaneous monitoring of multiple structures and their geodynamic context. This is particularly valuable for understanding whether observed deformations are structure-specific or part of broader regional phenomena such as subsidence. Modern high-resolution satellite constellations (e.g., COSMO-SkyMed, Sentinel-1) provide regular acquisitions every 3-12 days, enabling quasi-continuous monitoring when processed with advanced multi-temporal techniques. While this temporal sampling is discontinuous compared to ground sensors (with revisit intervals of days rather than continuous recording), it is sufficient for detecting progressive structural deformations and seasonal patterns. Satellite data excels at capturing the global deformation behavior of bridges, the overall settlement patterns, thermal deformations, and long-term trends, thereby guiding the placement and interpretation of ground-based sensors for detailed local monitoring. The effectiveness of InSAR for bridge monitoring stems from the distinct radar reflectivity properties of different surface materials. Bridge decks, typically constructed of concrete or steel, exhibit strong and stable radar backscatter,