GNSS Systems Unveil the Subtle Movements of Bridges
Long-span bridges are more than just feats of engineering. They’re living structures, constantly responding to the ebb and flow of natural forces and human activity. Be it the gusty wind sweeping across a Scottish loch or the unyielding flow of rush hour traffic, these structures are under constant stress. And while engineers have long measured displacement to monitor bridge health, that data alone has often left them peering into the unknown.
Enter a new game-changing methodology that’s turning heads in structural engineering circles. Developed by researchers at Southeast University, the Integrated Displacement and Attitude Determination (IDAD) system is rewriting the rules. Instead of treating displacement and attitude separately, the new approach combines them into a single, coherent picture—and does so in real time.
This leap forward isn’t just academic. It’s already been trialled on the Forth Road Bridge in Scotland, one of the UK’s most iconic and weather-exposed structures. The results: staggering accuracy and a potential revolution in how we monitor the bones of our built environment.
GNSS with Attitude
IDAD harnesses the power of multiple Global Navigation Satellite System (GNSS) antennas to capture both how a bridge moves and how it tilts, twists, and shifts—all in synchrony. The trick lies in combining this data through an advanced algorithm known as the Unscented Kalman Filter (UKF).
Unlike conventional two-step approaches that separately compute position and orientation, IDAD delivers it all in one go. The integrated model resolves GNSS ambiguities and fuses raw data, capturing even the subtlest of changes.
Field tests showed IDAD could measure displacement to sub-centimetre accuracy:
- Horizontal: 0.004–0.006 metres
- Vertical: 0.008–0.010 metres
And when it comes to attitude precision:
- Pitch: 0.0013 degrees
- Heading: 0.0004 degrees
Not bad for a system relying purely on GNSS over baselines as long as 2 kilometres. No inertial sensors required.
Insights from the Forth Road Bridge
It was during winter testing, when gale-force winds swept across the Firth of Forth, that IDAD’s real-world potential came to light. The system not only tracked displacements but also captured nuanced heading and pitch variations triggered by lateral winds and shifting temperatures.
These subtle shifts, often precursors to structural stress or fatigue, are precisely what traditional displacement-only systems struggle to detect.
“By integrating displacement and attitude into one estimation framework, we’re capturing a dimension of structural behaviour that has been largely overlooked,” explained Professor Xiaolin Meng, senior author of the study. “This level of insight allows us to better understand how bridges breathe and bend—vital knowledge for proactive maintenance and public safety.”
This integrated monitoring allows engineers to detect early warning signs before damage becomes visible. That’s not just clever—it could be lifesaving.
Why This Matters Globally
Infrastructure worldwide is ageing, and the stakes are only getting higher. In many regions, bridges built in the post-war boom are nearing the end of their design life. Extreme weather events, climate-driven thermal variation, and increasing loads from traffic have all become accelerants of deterioration.
This is where multidimensional monitoring becomes invaluable. Rather than relying on a piecemeal approach, IDAD offers a full-spectrum analysis of structural health. It doesn’t just flag movement. It interprets that movement in context.
Beyond bridges, IDAD holds promise for:
- Skyscrapers swaying subtly under wind loads
- Dams exposed to constant hydrostatic pressure
- Offshore platforms battling wave forces and shifting seabeds
And it does all this without the expense or complexity of coupling GNSS with inertial systems. That simplicity could prove a game-changer for cash-strapped municipalities and private infrastructure operators alike.
Laying the Groundwork for Digital Twins
The implications of IDAD go well beyond real-time monitoring. The precision and consistency of the system make it an ideal candidate for integration into digital twin frameworks. With continuous streams of accurate data on both displacement and orientation, engineers can build more responsive, more realistic models.
In turn, these digital twins can simulate stress over time, test emergency scenarios, or guide maintenance planning with surgical precision.
Moreover, the preservation of cross-correlation between displacement and attitude data—often lost in other systems—allows for a richer interpretation of the structural behaviour. It’s this holistic view that promises to redefine best practices in asset management.
Funding and International Collaboration
None of this innovation happened in a vacuum. The project is supported by the National Natural Science Foundation of China through their major programme “BeiDou/GNSS Multi-Sourced Data Fusion Theory and Digital Twinning Method for Real-Time and Condition Diagnosis of Large-Span Bridges” (Grant No. 42430711). Additional funding comes from the Fundamental Research Funds for the Central Universities.
The academic paper, published in Satellite Navigation in July 2025, is open access and already gaining attention across the global civil engineering community. The original publication can be found via DOI: 10.1186/s43020-025-00174-9.
Towards Smarter, Safer Infrastructure
What we’re seeing is a fundamental shift—from reactive repairs to proactive resilience. IDAD is ushering in a new era where structures don’t just sit silently but actively “talk” to engineers in real time.
This technology could serve as a cornerstone for next-gen urban planning, where live data feeds support dynamic load balancing, automated alerts, and smarter resource allocation. In places where maintenance budgets are stretched thin, the ability to pinpoint trouble before it escalates could offer a powerful return on investment.
In short, IDAD isn’t just another sensor system. It’s a tool for reshaping how we think about infrastructure. As cities expand and climate pressures mount, such innovations are no longer optional—they’re essential.
