Collection of Data with Unmanned Aerial Systems (UAS) for Bridge Inspection and Construction Inspection
Unmanned aerial systems (UAS) with high-resolution cameras and other sensors can be used to supplement bridge inspections near or into difficult-to-reach areas around and above the bridge, an activity that traditionally requires placing bridge inspectors at risk. The objective of this study was to explore the use of UAS to support bridge inspection and determine how effectively they can assist in routine inspections. State Department of Transportation (DOT) agencies were interviewed about their usage of UAS in bridge inspections. Three case studies discussed the inspections of Ticonic Bridge, in Maine (2017); a small bridge in Glenwood Springs, Colorado (2018); and an I-80 highway bridge in Salt Lake City, Utah (2020). Researchers then conducted field tests in Maine and a controlled laboratory test to determine the minimum system specifications (flight and sensor parameters) needed for effective UAS deployment. Field inspections utilized three commercially available UAS to evaluate and identify bridge defects. Based on the laboratory experiment, recommendations were made for baseline system requirements, sensor performance, and UAS distances in bridge inspections.
- Use UAS during routine inspections of large, long, and complex bridges. On such bridges, the reduction in time required for an inspection using a UAS, compared with that needed for a traditional routine inspection process, may allow bridge owners to inspect more bridges in a shorter period of time. The sole use of UAS for fracture critical member inspections is discouraged as UAS still have insufficient capability to see through dirt, debris, and corrosion that can hide critical defects. For this reason, the National Bridge Inspection Standards (NBIS) still requires a hands-on inspection of fractured critical members.
- Work with an experienced pilot to ensure proper safety and compliance. No matter the quality of the equipment, success in the field relies heavily on the UAS pilot. It is the pilot’s experience that will direct the UAS platform and sensor to the bridge defect, and the inspector’s expertise that will determine the severity of defect and whether further inspection is required. Pilots must be trained to operate in an environment lacking GPS. UAS flight paths must be planned to reduce the possibility of missing a defect in key structures and to ensure that inaccessible parts of the bridge are inspected.
- Ensure that inspectors can view real-time imagery. Otherwise, delays in identifying defects may not significantly reduce the time needed for inspection or warrant regular usage.
- Operate with wind conditions at 15 mi/h or less. Higher wind speeds generally degrade UAS flying qualities and the quality of the imagery, causing the resulting images become unusable for inspection purposes.
- Only adjust the UAS sensor’s automatic settings if absolutely necessary. This includes the ISO, shutter speed and aperture. When adjusting the settings manually, adjustment of one setting will typically require adjustment of another setting to maximize the potential to detect a defect. Incorrect adjustments can result in dark, grainy and blurry images. The camera’s ability to instantaneously and automatically calculate the appropriate settings will produce the highest quality results with the least amount pilot distraction.
- Specify a clearance (i.e., standoff distance) of five feet to ensure both usable imagery and safety of flight. With a UAS that has indoor stabilization capabilities, a relatively safe distance is approximately 5 feet, but this can be extended if the system has an optical zoom capability
- Keep maintenance logs to track the maintenance interval for each system. UAS equipment should be maintained according to manufacturer guidelines. Of particular importance are the procedures used to charge and maintain the batteries, the most common power source for multirotor systems.