Researchers from NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, and the University of Bath are developing a technique that uses satellite radar imaging to monitor the safety of bridges and other large-scale infrastructure. Using 15 years of orbital radar images of the Morandi Bridge, the researchers were able to detect signs of warping that preceded its collapse in 2018.

On August 14, 2018 at 09:36 GMT, a 690-ft (210-m) section of the Morandi Bridge that linked the Sampierdarena and Cornigliano districts in Genoa, Italy, collapsed during a torrential rainstorm, sending about 35 cars and three trucks plunging down into the Polcevera river, killing 43 people.

The cause of the collapse isn't entirely clear, but it appears that four of the bridge stays had corroded through and failed explosively, possibly set off by a lightning strike. Like many such structural accidents, it came as an almost complete surprise and sparked a political scandal about the state of infrastructure in Europe. However, the new study indicates that the signs of impending collapse were there, if it had been possible to see them beforehand.

"The state of the bridge has been reported on before, but using the satellite information we can see for the first time the deformation that preceded the collapse," says Giorgia Giardina, Lecturer at Bath's Department of Architecture and Civil Engineering. "We have proved that it is possible to use this tool, specifically the combination of different data from satellites, with a mathematical model, to detect the early signs of collapse or deformation."

According to the team, the new technique allows engineers to study an entire bridge rather than relying on the much more limited localized data coming from sensors. In addition, it can work in real time.

"The technique marks an improvement over traditional methods because it allows scientists to gauge changes in ground deformation across a single infrastructure with unprecedented frequency and accuracy," says Pietro Milillo of JPL. "This is about developing a new technique that can assist in the characterization of the health of bridges and other infrastructure. We couldn't have forecasted this particular collapse because standard assessment techniques available at the time couldn't detect what we can see now. But going forward, this technique, combined with techniques already in use, has the potential to do a lot of good."

The new technique relies on recent advances in satellite technology like those in the Italian Space Agency's COSMO-SkyMed constellation and ESA's Sentinel-1a and 1b satellites. These include Synthetic Aperture Radar (SAR) data that uses different angled radar beams to build up a 3D model of a target. Previous versions could only produce a resolution in the centimeter range, but the latest generation can manage models in the millimeter band that the team compares to Ultra-HD-TV in terms of detail.

"There is clearly the potential for this to be applied continuously on large structures," says Giardina. "The tools for this are cheap compared to traditional monitoring and can be more extensive. Normally you need to install sensors at specific points within a building, but this method can monitor many points at one time."

In addition to above-ground structures, the satellite monitoring can keep an eye on underground works by measuring the shift in buildings on the surface. The technique is already being considered for use in Britain to monitor road and railway networks.

The study was published in the journal Remote Sensing.