Researchers from the Alfred Wegener Institute recently programmed a multi-rotor unmanned aircraft system (UAS) to fly autonomously through remote expanses of the Arctic Ocean and land on an ice floe.
Engineers on board the institute's research icebreaker Polarstern specially programmed the UAS, which was able to navigate despite the deviations produced by the Earth’s magnetic field near the North Pole.
“At high latitudes, autonomous navigation is a major challenge,” explains Sascha Lehmenhecker, an engineer at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). “Navigation systems normally use magnetic sensors. But near the poles, the lines of the Earth’s magnetic field are nearly perpendicular to the ground, making precise navigation extremely difficult. That’s why commercial multicopter control systems aren’t well suited for use in polar regions.”
With PhD candidates Michael Strohmeier and Tobias Mikschl from the University of Würzburg, Lehmenhecker refined the control systems for the UAS to land on ice floes and autonomously fly back to the mother ship several hours later.
In this case, both the ice floe and the ship were in motion. The ship had to continue on its scheduled course to conduct other research while wind, waves and currents caused the ice floe to drift – and it was precisely the direction and speed with which it drifted that the UAS needed to determine.
The development team pursued two approaches to allow the multi-rotor’s control system to compensate for the distortions in the positioning.
“In the first approach, the multicopter remains in constant contact with a receiving station, which uses the copter’s GPS data to calculate the discrepancies. In other words, the multicopter transmits its GPS position to the station, which, in turn, transmits back the corresponding, adjusted coordinates,” says Lehmenhecker.
Or, he says, “We use two onboard GPS receivers to calculate the actual change in the copter’s position. Though this is the better method, it’s also much more complex, and we’re still just starting to develop it.”
The system passed its first test – conducted on an ice floe in the arctic Fram Strait – with flying colors: The team and copter were left on a floe.
Then cleared of the magnetic interference produced by electric motors on board the Polarstern, the team manually flew the UAS roughly three kilometers out, to the edge of visual range. They then activated the autonomous return program, and the aircraft flew to the pre-set coordinates and safely landed on its own.