Since the early 2000s, flocks of birds have been the number one cause of small-plane crashes, as well as two major U.S. aviation disasters to date. Between 2011 and 2014, approximately 67,000 bird strikes were recorded, with the number of collisions increasing by 10 percent annually. While 65 percent of bird strikes cause little to no damage to aircraft, the thousands of occurrences each year due to birds is too alarming to ignore.
After the notable “Miracle on the Hudson” back in 2009, where US Airways Flight 1549 struck a flock of geese shortly after takeoff and pilots Chesley Sullenberger and Jeffrey Skiles were forced to land in the Hudson River off Manhattan, Soon-Jo Chung, a researcher at Caltech's Center for Autonomous Systems and Technologies, felt it was time for a solution. Along with other Caltech engineers, they were able to develop a control algorithm that allows a drone to herd flocks of birds away from airspaces around airports.
"The passengers on Flight 1549 were only saved because the pilots were so skilled," says Soon-Jo Chung, the principal researcher on the drone herding project. "It made me think that next time might not have such a happy ending. So I started looking into ways to protect airspace from birds by leveraging my research areas in autonomy and robotics."
According to the team, they came up with strategies on how to modify airspace environments to become less attractive for birds. This means using trained falcons or piloting drones to scare off flocks—both of which have proven to be significantly costly. Additionally, it can be also unreliable in varying scenarios, making results unpredictable. Eventually, they came up with a better solution: autonomous herding drones.
“Herding relies on the ability to manage a flock as a single, contained entity—keeping it together while shifting its direction of travel.” This means that each bird in a flock reacts to changes in the behavior of the birds closest to it, synchronizing their movements with one another’s. In order to herd effectively, an external threat must be present. In this case, the herding drone has to encourage the birds along the outside of the flock to change course, forcing the whole flock to follow. However, this still requires precise positioning. Any erratic effects can induce the birds to panic and act individually instead of collectively.
To achieve this, the engineers “studied and derived a mathematical model of flocking dynamics to describe how flocks build and maintain formations, how they respond to threats along the edge of the flock, and how they then communicate that threat through the flock.” Taking inspiration from sheep herding, their work improves the process, which was able to function in only two dimensions.
"We carefully studied flock dynamics and interaction between flocks and pursuers to develop a mathematically sound herding algorithm that ensures safe relocation of flocks using autonomous drones," says Kyunam Kim, postdoctoral scholar in aerospace at Caltech and a co-author of the study.
Similarly, the researchers reverse engineered the process to observe exactly what kind of external threats flocks actively respond to. With that information, they were able to develop a new herding algorithm that produces ideal flight paths for incoming drones to move the flock away from a protected airspace without dispersing it.
"My previous research focused on spacecraft and drone swarms, which turned out to be surprisingly relevant for this project," Chung says.
The algorithm was tested on a flock of birds in Korea and discovered that a single drone is able to keep a flock of dozens of birds out of a designated airspace. According to Chung, “the effectiveness of the algorithm is only limited by the number and size of the incoming birds.” The team plans to explore how to scale the project to allow for multiple drones dealing with multiple flocks.
The study, titled "Robotic Herding of a Flock of Birds Using an Unmanned Aerial Vehicle," appears in IEEE Transactions on Robotics. The research was supported by the National Science Foundation.
For more stories on drone technology, check out how Drones Could Team Up to Rescue People in Danger.