MnDOT is researching how data and images collected by drones, 
such as the Aeryon Skyranger shown here, could aid bridge inspectors.

Using drones to inspect bridges

MnDOT is researching how data and images collected by drones, such as the Aeryon Skyranger shown here, could aid bridge inspectors.
MnDOT is researching how data and images collected by drones, such as the Aeryon Skyranger shown here, could aid bridge inspectors.

In recent years, drones made headlines for fighting wars overseas, detecting crop conditions, keeping an eye on power lines and even delivering retail goods.

As the flying electronic devices became easier to use and less expensive, all sorts of individuals, businesses, nonprofit groups and government organizations – including the Minnesota Department of Transportation (MnDOT) – are exploring ways to use them.

This past summer, MnDOT began researching how to employ these unmanned aerial vehicles, or UAVs, to someday help inspect the state’s many bridges.

“That day may still be far off, but our initial project was an encouraging first step,” said Jennifer Zink, MnDOT bridge inspection engineer. “Phase 2 of the project will better provide details as to methods, criteria and cost effectiveness for how to apply drone technology best to bridge inspection.”

Project goal

Using drones could also minimize risks associated with current bridge inspection methods, which include rope systems and special inspection vehicles. (Photo by D.R. Gonzalez, MnDOT)
Using drones could help minimize risks associated with current bridge inspection methods, which include rope systems and special inspection vehicles. (Photo by D.R. Gonzalez, MnDOT)

The research team tested drones this past summer while inspecting four Minnesota bridges (in Chisago County, Olmsted County, Morrison County and near Stillwater) specifically selected for the study after an extensive evaluation and FAA approval.

Zink and her colleagues wanted to investigate whether drones could help MnDOT decrease the rising costs of bridge inspections and collect more detailed information. Drones could also minimize the risks for bridge inspectors, who currently use rope systems and special inspection vehicles to access hard-to-reach areas. Using a drone to gather images could keep inspectors out of harm’s way and inspection vehicles out of active traffic lanes.

“The goal of the project was to study the effectiveness and possibilities of using UAVs to aid in bridge inspection work, typically in gathering images without the use of an under-bridge inspection vehicle and in areas where access is difficult or not safe for an inspector,” Zink said. “There is no substantive guidance in existence for this application of this evolving technology. This initial effort was to gain a better understanding of potential capabilities, processes and planning best practices.”

FAA approval

Before simply launching drones and collecting bridge data, the research team reviewed current FAA rules and applied for the necessary exemptions. Approval was granted, but only for the use of an Aeryon Skyranger drone. Even though exemptions for several models were submitted to the FAA, none were approved in time for the field study.

The team, which included personnel from Collins Engineers Inc. and Unmanned Experts, also worked closely with the MnDOT Office of Aeronautics to plan the project and gain the necessary approvals. The Aeronautics Office recently published an official MnDOT drone policy.

In the air

Once in the air, the drone suitably performed a variety of inspection functions that didn’t require a hands-on physical inspection. Researchers tested the drone’s ability to gather high-quality still images and video footage of bridges. They also collected data from infrared cameras. In addition, the drone provided the ability to capture data needed to construct maps of bridge areas and 3D models of bridge elements.

“The images, including infrared images to detect deck trouble spots, obtained from the drone correlate to the findings in the bridge inspection reports for specific bridge elements,” Zink said.

Missing from the research were images of the underside of bridges. The drone model used in the study wasn’t able to shoot images upward from beneath a bridge, and inspectors identified that as a key feature along with the ability to operate without a GPS signal.

“The drone we used in this project was not completely ideal for an entire gathering of imagery for all bridge inspection elements as it was limited to GPS signal capability,” Zink said. “However, it did give us an idea of what a drone could provide, what the limitations were, and what features we would like to see on newly available UAV models. Unfortunately, our hands were tied with obtaining FAA exemptions only for the particular model used in this project within the funding timeframe.”

Conclusions and recommendations

The project’s final report listed several conclusions, including that drones can be used safely during bridge inspections and that risk to both the inspectors and public is minimal.

“Due to the successful outcome of the initial project, we have a better understanding of the drone capabilities we would like to use during an actual scheduled bridge inspection,” Zink said. “The drone that will be used in Phase 2 is specifically designed for inspection of structures. Several goals exist for the Phase 2 research project, and if we can accomplish them, they will decrease MnDOT’s costs and increase bridge inspection abilities. It could improve inspection data collection for local agencies as well.”

The researchers recently were notified that they received funding for Phase 2 of their project, which is expected to start later this fall.

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