# Interpretation of Bridge Health Monitoring Data from Satellite InSAR Technology
## 5 Conclusions  
This paper presents an application of satellite InSAR technology for the remote monitoring of a prestressed concrete bridge--the A22 Po River Bridge in Italy--and the interpretation of results from a structural standpoint. Specifically, 109 Cosmo-SkyMed X-band SAR images covering eight years have been analysed through MT-InSAR, and the displacement time series of the PSs identified on the bridge have been (i) compared to the expected response of the bridge to temperature variation and (ii) correlated to environmental loads. All of that is to verify the effectiveness of satellite InSAR in providing reliable information on the structural behaviour of bridges and the possibility of identifying different responses in different bridge components (e.g., access lanes, piers, spans, fixed and roller bearings) and unexpected behaviour. The MT-InSAR analysis identified 8426 PSs on the almost 1 km-long bridge, with deformation velocities along the LoS ranging from \(-2.5\) to \(0.5\) mm/year, velocities' standard deviations between 0.21 and 0.56 mm/year, and temporal coherence higher than 0.7. Unexpected deformation velocities have been observed over the southern access lane, an issue the infrastructure operator is already addressing, and over the Pier 11, which underwent significant erosion at its base in the past. Focusing on the piers, we verified that the periodicity and magnitude of the displacements observed through satellite InSAR are consistent with this bridge's expected temperature response. Moving on to the cantilevers, we observed that their horizontal longitudinal displacements in response to temperature variation can be observed with satellite InSAR. Moreover, and most importantly, it is possible to identify different spans and piers of the bridge simply by studying the sign of the correlation between displacement and temperature variation and its periodicity along the bridge length. However, this result is strongly related to the bridge orientation. Further studies on different case studies are recommended to investigate the impact of bridge orientation on the effectiveness of satellite InSAR-based SHM performances. Finally, this study highlights the influence of river water level variations on piers displacements in the riverbed, emphasising the need to consider environmental factors and geotechnical characteristics of the foundation soils in bridge monitoring. In conclusion, this study confirms the potential of satellite InSAR technology for the remote monitoring of road bridges and the surrounding territory without installing any sensor on site, which can foster an extensive remote SHM of civil infrastructure, potentially solve the high-cost issue of traditional contact-type sensors, and dramatically improve SHM-based bridge management. However, the performance of this remote monitoring technique should be further investigated through a direct comparison with measurements from traditional technologies. Conceptualization, D.T. and V.F.C. ; data curation, A.R. and R.T.; formal analysis, D.T. and A.R. ; funding acquisition, D.T. and D.Z. ; investigation, D.T. and V.F.C. ; methodology, D.T. and V.F.C. ; project administration, D.T. ; resources, D.T. and A.R. ; software, A.V. ([PERSON]) and R.T.; supervision, A.V. ([PERSON]), D.P. and D.Z. ; validation, A.V. ([PERSON]) and D.P. ; visualization, D.T. and A.V. ([PERSON]); writing--original draft, D.T. ; writing--review and editing, D.T. All authors have read and agreed to the published version of the manuscript.