Navigation satellites are intended to monitor the infrastructure

From a purely external perspective, the Kölnbrein Dam in Carinthia, operated by Verbund, as the tallest dam in Austria, and the DC Tower in Vienna, as the tallest building in Austria, do not have much in common, but for a research group led by Caroline Schönberger and Werner Lienhart from the Institute for Engineering Geodesy and Measurement Systems at the Technical University of Graz, they are scientific but equally interesting. Measurements on these two structures allowed the team to develop a satellite-based method for static and dynamic monitoring of critical infrastructure as part of the InfraHealth project.

This makes it possible to monitor slow deformations, which arise for example due to changes in the level of the dam in a dam, and not just through static measurements. Dynamic measurements can also be used to register building vibrations and detect damage or other critical changes based on deviations. Until now, different methods had to be used for static and dynamic measurements. The new method also enables continuous monitoring, even in rain, snow, fog or storms.

Unique accuracy
“The high level of accuracy we were able to achieve with the measurements in the InfraHealth project, funded by the FFG, is virtually unique,” ​​says project manager Caroline Schönberger from the Institute for Engineering Geodesy and Measurement Systems at the Technical University of Graz. “We can detect vibrations in the millimeter range or even less using satellites located about 20,000 kilometers away from us. This project paves the way for the widespread use of Global Navigation Satellite Systems (GNSS) for static and dynamic monitoring of critical infrastructure and thus for continuous monitoring of its safety, independent of environmental influences. Not only building operators benefit from this, but also their users.”

This new measurement method uses local antennas and the publicly available GNSS signals from Galileo, GPS and GLONASS satellites. The antennas are attached to relevant measuring points on the structure; another, so-called reference antenna, is located relatively close by on a stable surface. The antennas determine their position via the satellites, with dynamic measurements every 0.05 seconds, so with a frequency of 20 Hertz. GPS and Galileo signals have proven useful for the determination here, as they allow the antennas to record their position more reliably. Using this captured raw data, the researchers calculate the frequency response of the structure.

Planning with Virtual Reality
The static measurement is more comfortable because the measurement evaluation has a fixed interval that is certainly longer than a second – it can also be an hour or a day. Here the combination of all three GNSS systems produced the best results; GLONASS was also added to Galileo and GPS.

To ensure in advance that the antennas at the intended measuring points will be in contact with the satellites, the research team developed a tool that allowed them to carry out the entire planning in virtual reality. At the Kölnbrein Barrier, the team determined in advance that not only the two antennas in the middle and halfway along the wall could receive sufficient satellite signals, but also at the very edge. The transition to solid ground is especially important when monitoring dams.

Earthquake measured 550 kilometers away
Instead of six antennas, the DC Tower team only needed two: one to measure the building’s frequency and one to check whether the building is rotating due to outside influences, such as wind. The tests there showed how accurately the new process can detect changes. During the series of measurements, the tower’s movements allowed the researchers to capture the traces of an earthquake about 550 kilometers away in northern Italy. The 5.7 magnitude earthquake occurred on November 9, 2022 at 7:07 a.m. Central European Time near the Adriatic coast northwest of Ancona. Earthquake waves travel at a speed of about 3 kilometers per second, so in three minutes they travel about 540 kilometers and at 7:10 am there was a similar rash at the DC Tower.

Werner Lienhart, head of the Institute for Engineering Geodesy and Measurement Systems at the Graz University of Technology, adds: “The combination of static and dynamic monitoring of infrastructure in one measurement system makes it possible to gain a deep insight into the current health status of a structure. This is especially important for large structures such as bridges or dams that are nearing the end of their planned lifespan.”

Partners of TU Graz in the InfraHealth project were: Verbund Hydro Power GmbH, Leica Geosystems Austria GmbH, Disaster Competence Network Austria, pentamap GmbH. The research project is anchored in the field of expertise “Information, Communication & Computing”, one of the five strategic focus areas of TU Graz.