Bridge Collapse Revealed by Multi-Temporal SAR Interferometry
Sousa, Joaquim1; Bastos, Luisa2
1University of Tras-os-Montes e Alto Douro, PORTUGAL; 2University of Porto, PORTUGAL

On the night of March 4, 2001, the Hintze Ribeiro centennial Bridge, made of steel and concrete, collapsed in Entre-os-Rios (Northern Portugal), killing 59 people, including those in a bus and three cars that were attempting to reach the other side of the Douro River. It still remains the most serious road accident in the Portuguese history.
According to national authorities, the collapse was due to two decades of illegal but allowed sand extraction which compromised the stability of the bridge's pillars, as well as disregard from the responsible officials despite the warnings of divers and technicians.
In this work we do not intend to corroborate or contradict the official version of the accident causes, but only demonstrate the potential of Multi-Temporal Interferometric (MTI-InSAR) techniques for detection and monitoring of deformations in structures such as bridges, helping to prevent new catastrophic events.
Based on the analysis of 57 ERS-1/2 covering the period from December 1992 to the fatality occurrence, we were able to detect significant movements (up to 20 mm/yr) in the section of the bridge that fell in the Douro River, obvious signs of the bridge instability.
These promising results make it possible to think in the development of an interferometric methodology using the new high-resolution synthetic aperture radar (SAR) satellite, with a spatial resolution of up to one meter, for structural health monitoring (SHM).