A structured Delft–Amsterdam research collaboration integrates bridge typologies, expected failure mechanisms, and satellite viewing geometry to translate one-dimensional MT-InSAR measurements into practical damage indicators, demonstrating how regional-scale millimetre-level displacement data can support systematic structural evaluation of urban bridge networks.
The Urban Bridge Monitoring Dilemma
Across Europe and beyond, bridge networks are aging under increasing traffic demand and environmental stress. Many assets were not designed for today’s loading conditions, and replacement or strengthening programs require substantial financial investment.
Amsterdam provides a particularly demanding case study. The city manages approximately 1,800 bridges, many founded on wooden piles and constructed centuries ago. These structures are located on soft clay and peat soils prone to long-term subsidence. Differential settlement and foundation-related mechanisms therefore represent relevant structural concerns.
In response, the municipality initiated the Bridges and Quay Walls (PBK) program in 2018, targeting 820 bridges and more than 200 km of quay walls for investigation, monitoring, and rehabilitation. Given the scale of this effort, scalable monitoring approaches are of clear interest.
The Opportunity—and the Constraint—of MT-InSAR
Multi-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR) enables millimetre-scale displacement measurements across large areas using satellite data. It operates remotely, without on-site instrumentation, and supports long-term retrospective analysis.
However, as clearly stated in the research, MT-InSAR reconstructs displacement only along the satellite Line of Sight (LOS). Because typically only one or two viewing geometries are available, the full three-dimensional displacement field cannot generally be reconstructed.
For bridge assessment, this is a critical limitation. Without accounting for expected motion directions and the asset’s orientation relative to the satellite flight path, displacement magnitudes may be underestimated and misinterpreted.
The study does not attempt to eliminate this limitation. Instead, it proposes a structured way to work within it.
From Raw Displacements to Structural Insight: The Proposed Framework
The authors introduce a methodology that integrates bridge typologies, anticipated failure mechanisms, and satellite geometry to derive tailored damage indicators. The approach was implemented on 505 Amsterdam bridges using TerraSAR-X descending data from 2016–2020.
The workflow can be summarised in four key components.
1. Building a Regional GIS Bridge Inventory
Bridge deck geometries were extracted from the Dutch Basic Register Large-Scale Topography (BGT). To account for Permanent Scatterer (PS) geolocation uncertainty and include abutment regions, each deck polygon was expanded with a 6 m buffer.
The geometries were enriched with municipal bridge data, including typology, material, usage, and construction year.
2. Linking Typologies to Likely Failure Mechanisms
Using a Bridge Failure Mechanism Report provided by the municipality, fixed bridges were classified by foundation type:
- Wooden piles (with or without intermediate supports)
- Concrete or steel piles (with or without intermediate supports)
- Unknown typology
Movable bridges were excluded due to their complexity.
For each typology, likely failure mechanisms detectable within InSAR timeframes were identified. In Amsterdam’s soft-soil conditions, these primarily involve vertical settlements, abutment rotations, and related deformation patterns.
This classification step provides the basis for defining expected displacement directions.
3. Evaluating Satellite Sensitivity Through Bridge Orientation
TerraSAR-X descending orbits are approximately North-South.
Each bridge’s longitudinal axis was compared with this direction. Two categories were defined:
- Bridges with longitudinal axes nearly parallel to North–South
- Bridges with longitudinal axes orthogonal to North–South
Assuming negligible transversal displacement (a reasonable assumption for Amsterdam’s conditions as stated in the paper), LOS measurements for bridges parallel to the satellite track can be interpreted as projections of vertical displacement.
Bridges orthogonal to the orbit would require data from multiple geometries for full decomposition. In this study, only the parallel-aligned bridges were further analysed.
4. Deriving MT-InSAR-Based Damage Indicators
For selected bridges, PS displacements were projected along the longitudinal axis and interpolated using a quadratic polynomial to reconstruct the vertical displacement profile.
Two indicators were then calculated:
- Angular distortion between abutments
- Deflection-to-span ratio
These indicators are consistent with settlement-related damage scenarios identified for Amsterdam bridges.
Findings from 505 Amsterdam Bridges
The methodology was applied to 505 bridges across the city.
For representative cases, displacement profiles showed settlement patterns concentrated near abutments, consistent with foundation behaviour on compressible soils.
Across the analysed bridges:
- Angular distortion values remained below 0.005
- Only six bridges showed values between 0.003 and 0.005
Within the 2016–2020 observation window, the results indicate limited differential settlement within the detectable range of the MT-InSAR dataset.
The study concludes that integrating GIS bridge data, typology-based assumptions, and satellite geometry enables regional-scale bridge condition evaluation in scenarios involving vertical movement.
Implications for Infrastructure Management
The research does not position MT-InSAR as a standalone replacement for inspection or structural analysis. Rather, it demonstrates a structured way to interpret one-dimensional satellite measurements in the context of known structural behaviour.
For municipalities managing large bridge inventories, such frameworks can support:
- Network-level screening
- Identification of assets exhibiting measurable deformation trends
- Prioritisation of further investigation
As satellite archives expand and processing techniques mature, structured integration with asset databases may play an increasing role in infrastructure monitoring strategies.
Reference
Macchiarulo, V., Kuai, H., Karamitopoulos, P., Milillo, P., & Giardina, G. (2024). Structural evaluation of urban bridges in Amsterdam through InSAR-based displacement data. e-Journal of Nondestructive Testing. https://doi.org/10.58286/29731