Davis Ferry Park Bridge Scan

    The objective of this project was to obtain a 3D scan of the both the inside and outside of the footbridge over the Wabash River located at Davis Ferry Park using the Skydio 2+ platform.

Hazard Assessment

    The Davis Ferry Park bridge is a hazard rich environment, particularly for UAS operations. Physical attributes of the bridge and its surroundings that were determined to be hazardous upon inspection include trees, power lines, thin metal beams within the bridge structure, high water, wind from the river channel, and wildlife. Metal objects such as beams, or power lines can cause a multitude of issues with flight. Magnetic interference from metal or the power lines can disrupt the GPS strength and cause errors with the positioning system. Additionally, objects less than one half inch in diameter (i.e. thin beams, power lines, or tree branches) may not be detected by the vision sensors and leave the UAS vulnerable to a collision. To avoid this problem, strict geofences were set to avoid the powerlines and dangerous parts of the bridge that were not too be included in the scan.

    The water under the bridge also provided numerous hazards. First and foremost, the water was particularly high during the time of the scan. Consequently, the bridge was only accessible from one side and the only available location for takeoff was on the bridge itself. The high and fast-moving water also facilitated in increase in wind speed around the bridge, making it difficult to find a safe time to fly that was within the limits of the UAS. It should also be noted that due to its reflectivity, vision sensors often have a difficult time detecting water, making flights over water particularly hazardous. A strict floor was set to avoid the UAS coming in contact with the water.

    The wildlife also posed a potential threat to the operation. Numerous birds such as pigeons, geese, ducks, and even bald eagles were observed to be frequent visitors to the environment surrounding the bridge. While pigeons typically fly away when started, geese are known to be territorial and predatory birds such as bald eagles are even known to mistake a small UAS for prey. Caution was taken and the VO notified if any birds appeared to enter the flight area. 

    One final hazard associated with the Davis Ferry Park bridge was other people. Given that this is a public park it was expected and anticipated that pedestrians may desire to cross the bridge during flight, however due to the high water blocking one entrance to the bridge, none were encountered. Additionally, several homes were located along the Wabash River next to the park, and it would have been reasonable to expect the homeowners to appear with questions or concerns about our operation, however this was not an issue. 

Operation

    Despite all of the aforementioned hazards, the two flights were both conducted relatively smoothly and without issue. We were able to take off from the bridge in the gaps between the trusses. From the perspective of a VO or PIC, I will admit it was nerve-wracking watching the Skydio 2+ weave in between each of the beams on the bridge, but we trusted the technology and it delivered without incident. A decent amount of tuning of the scan settings was required before flight in order to balance quality, time, and battery usage. At first, we started off with the speed set low as a concern for safety, but quickly realized that this would take entirely too long and use more batteries than we had on site. The settings we ultimately decided to use were 60% overlap and sidelap, 30ft distance to surface, and 5mph speed. Overall, 2 successful scans were produced, although quality was dropped slightly in order for the UAS to move slower and safer. After completing 2 successful flights with these settings, I might consider increasing the speed slightly. This would allow for higher overlap, sidelap, better distance to surface, and overall better quality simply because the drone is moving between each picture faster which allows for more data recorded in one battery cycle.