FHWA Study Using Laboratory Testing of Unmanned Aerial Systems Offered Lessons on Factors Affecting System Efficiency for Decision Makers and Stakeholders.
Controlled-Environment Testing of UAS Digital Camera Sensor Specifications and Operational Parameters for Bridge Safety Inspections
Bridge inspection programs incorporating Unmanned Aerial Systems (UAS) to enhance the inspection process are becoming more and more widespread, which in turn renders it essential to make sure these advanced inspection tools meet the optimum specifications for obtaining high quality imagery for bridge owners and inspectors. This study was conducted at the University of Maine in a laboratory setting to capture and analyze data that would potentially aid decision makers when considering integrating UAS into their inspection programs. The laboratory testing was performed over a three-day period in December of 2019 using three aircrafts with different sensor systems to explore the factors that may impact the quality of the inspection imagery.
- Ensure favorability of weather conditions and wind speed at the Inspection site prior to UAS takeoff. This is important as wind speeds of more than 15 mi/h generally degrade the stability of the UAS and thus the quality of the imagery so much that it is not usable for inspection purposes.
- Check sensor resolution and settings to ensure its ability to produce quality images. Testing in this study found that the most effective and practical mode for sensor operation is using the automatic settings, which can reduce the time needed for postprocessing and the number of tasks an individual is responsible for during the fly. Study results also suggest that the camera should offer manual adjustment functions of the ISO setting from 100 to 3,200 and allow users to manually change the shutter-speed setting, which controls exposure, from 1/15th to 1/100th of a second.
- Maintain a standoff distance of at least five feet. This, coupled with a camera with optical zoom capability, would produce inspection-quality images and reduce the likelihood of the aircraft colliding with the structure being inspected.
- Consider augmented lighting. Use of external lighting would become especially necessary in low-light conditions to improve the image quality. Manual adjustment of camera settings tends to adversely affect image quality, often making the images blurry due to the motion of the UAS. Using external lighting can sufficiently light the foreground, allowing the camera’s automatic setting adjustments to capture images with the highest quality.