1.1. Ideal Operational Scenario
In this scenario, operations take place during daylight hours, in good visibility conditions acceptable for UAV operations, no roadway or pedestrian traffic, and at least five miles away from any other aviation activity. Also, this scenario assumes that the FDOT performed the planning of the inspection and a hands-on inspection is not required and the inspection to be performed is a routine one.
In order to gather visual information of the bridge with the new system, the process starts by the inspection crew (team leader, an assistant bridge inspector, visual observer, UAV pilot, and UAV operator) arriving to the inspection site. The team leader and the assistant bridge inspector record the basic information such as bridge location, bridge orientation, inspection crew, air temperature, weather conditions, and time. In the meantime the UAV the pilot, UAV operator, and visual observer start setting up the UAV, the image acquisition system, and the base station or visual interface for the inspection. Before taking-off, the pilot verifies the battery status of the UAV and the operator verifies the battery status of the image acquisition system and that it is capturing and transmitting video feed to the visual interface. This UAV system has the ability to fly without GPS signal and the image acquisition system has the ability to look upward.
Usually, the team starts by inspecting the deck. The UAV system equipped with the image acquisition system flies over the surface of the bridge. The deck inspection can take between 10 to 15 minutes. The team leader and the assistant bridge inspector guide the pilot to focus on specific areas of interest (e.g., bearings, signs of cracking, corrosion, and spalling) based on the video feed streamed to the visual interface in near real-time. The team leader annotates the areas of interest. While the UAV is flying, the visual observer keeps communication checks with the pilot and scan for unexpected aircraft activities, birds, people, and traffic. After the deck is inspected, the pilot verifies the remaining flight time of the system. If it is necessary the UAV returns to the base station and the batteries are replaced. Then, the inspection crew proceed to collect visual data of the superstructure, as well as the substructure following a similar procedure to the one described above (inspecting the superstructure usually takes between 15 to 20 minutes, while inspecting the substructure takes around 10 to 15 minutes). While inspecting the superstructure, special attention is given to the bearings or connections since they provide the critical link between the superstructure and the substructure and are usually located at challenging locations. The video feed from the image acquisition system in the UAV is autosaved in the visual interface, so the team leader and the assistant bridge inspector have access to the images to report the observations.