PSI - Issue 84

Mario Costantini et al. / Procedia Structural Integrity 84 (2026) 859–866

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4. Applications and future developments Satellite SAR offers distinct advantages over in-situ techniques, providing wide-area coverage and remote, all weather safety. While not replacing precision instrumentation, it effectively highlights anomalies to guide detailed inspections. A key preventive application is resonance-risk screening: mapping fundamental frequencies creates a screening layer that complements engineering inventories and prioritizes retrofitting. SAR is ideal for repeat observations, enabling baseline creation and trend monitoring essential for Structural Health Monitoring (SHM). By tracking modal frequency changes linked to stiffness loss or damage, it provides dynamic indicators that complement InSAR measurements. For bridges, this facilitates cost-effective network monitoring, supporting anomaly detection where dense sensor deployment is prohibitive while seamlessly integrating with ground instrumentation. These advantages align with EU Directive 2022/2557 (CER) on critical entity resilience. SAR provides scalable indicators that enhance situational awareness, while future integration with in-situ data supports rapid post-event assessments and technology-driven resilience. However, challenges remain: i) Clutter and low SCR: they can overwhelm weak scatterers, degrading both tracking and phase-driven estimators; ii) Vibration amplitude fidelity: it is generally more sensitive to phase noise and model mismatch than vibration frequency estimation; iii) Geometry dependence: variations in acquisition geometry can modify scattering mechanisms, affecting parameter repeatability; iv) Parameter Sensitivity: scalability challenges require automated parameter selection and robust quality scoring, and aggregation across multiple points. To address these issues, research should focus on three priorities: (1) algorithmic advances toward global structural models and hybrid pipelines; (2) automation through systematic or learning-based parameter selection and quality control; and (3) standardized products (baselines, reliability scores) that integrate into SHM workflows. Operations can be based on cloud platforms for managing and processing high-resolution SAR streams. The adoption of OGC/INSPIRE standards is essential for interoperability. In this context, geospatial platforms serve as integrative layers, combining SAR indicators with infrastructure inventories and sensor data. This enables dynamic structural assessment and resilience monitoring, directly supporting the risk assessment and reporting requirements of the CER Directive. Furthermore, harmonized standards facilitate cross-border data exchange. Ultimately, the integration of Micro-Doppler SAR products into these cloud enabled environments is a critical step toward actionable and policy-relevant resilience assessment, both in preventive and post-event contexts. 5. Conclusions This work presented a unified view of satellite SAR Doppler-variation sensing, demonstrating that both Sub-Pixel Offset Tracking (SPOT) and Doppler Phase Coherence (DPC) are effective estimators for structural vibrations. Comparisons with ground-truth data from the South Portland Street Suspension Bridge confirmed high accuracy in identifying dominant frequencies and nodal behaviours. Consequently, this Micro-Doppler approach offers a promising tool for urban monitoring and structural health assessment, particularly in seismic zones. By providing critical degradation indicators, these methods can complement standard analyses and support decision-making in alignment with the resilience requirements of EU Directive 2022/2557. 6. Acknowledgments This work was partially funded by the European Space Agency (Contracts 4000142119 and 4000142272/23/I DT), the ReLUIS Consortium (DPC-ReLUIS 2020-2026 WP6), and the European Union–Next Generation EU (CUP E53D23003560006). We thank Umbra Space, Glasgow City Council, and the Universities of Trento and Strathclyde for imagery, site authorization, and testing support. Finally, we acknowledge ESA’s E. Imbembo, M. Zimmermanns, and M.M. Corvino for their support, as well as A. Vattulainen and A. Lotti for providing SPOT results and ground truth data.