Comparing the Accuracy between UAS Photogrammetry and LiDAR in Bridge Inspections

Unmanned Aircraft Systems (UAS) have been increasingly used in the inspections of civil infrastructure due to their superior capabilities of fast deployment, comprehensive coverage, and labor-saving field operations. Depending on the use of the infrastructure, while some of them allow a visual check of the structural integrity, others require accurate inspection and verification of the structural members to resist natural hazards, such as flooding and hurricane. Photogrammetry and LIDAR are the two most commonly applied techniques among UAS inspection approaches. With the vast variety of available UAS airframes, navigation systems, and measurement sensors, the results of UAS inspections are not always consistent and comparable. This study presents the findings of measurements between a commercial photogrammetry UAS system and a customized LIDAR UAS system in bridge structure inspection. The measurements from two UAS systems were compared against the bridge plans and analyzed in terms of the span, deck, and foundation, and the results suggested that most UAS measurements are within 1% of the design values. The findings of the study demonstrate the workflow of using a UAS system for infrastructure inspection with both photogrammetry and LIDAR sensors and provide valuable insights into the accuracy of both UAS inspection techniques.