Testing and Evaluating the Impact of Illumination Levels on UAV-assisted Bridge Inspection

Unmanned Aerial Vehicles (UAVs) are increasingly being used in different civil infrastructure applications. UAV-enabled bridge inspection is being explored by many Departments of Transportation and the Federal Highway Administration in the USA due to the numerous benefits it brings to make the inspection process safer, cheaper, and more efficient than traditional inspection methods. One important criterion that influences the selection of UAVs for bridge inspection is the UAV's camera performance under different illumination levels. The illumination level becomes more crucial when inspecting elements of the bridge beneath the deck and in other less-illuminated areas of the structure. Since most of general-purpose UAVs usually come with a fixed camera, it is important to explore how different UAVs will perform under a given illumination condition. In this study, a procedure to test and evaluate the performance of different UAVs' cameras under different lighting conditions was developed. An image of a test element was captured under different lighting conditions with different UAVs. Entropy, which is a measure of the expected value of information content, was used to assess the quality and sharpness of the captured images. As observed in experimental results, UAVs with better-performing cameras exhibit higher entropy under similar conditions.