Vision-based lifespan and strength estimation of sub-cumulus thermal updrafts for autonomous soaring

This work focuses on the remote sensing of thermal updrafts under cumulus clouds for glider UAVs. Previous remote estimation techniques assume unlimited thermal lifespans under the clouds. Naturally occuring thermals are however of limited duration which increases the risk of an outlanding when utilizing these methods. By observing the evolution of the cloud's diameter, human glider pilots draw conclusions on both the lifetime and the strength of the related updraft. To bring this capacity to autonomous soaring UAVs, an Unscented Kalman Filter (UKF) is designed in this work for remotely estimating the vanish time and strength of a sub-cumulus thermal updraft. Nonlinear simulations including the dynamics of a small UAV glider as well as a realistic degree of noise are performed to demonstrate the estimation performance. Additional simulations show the benefit of considering temporally limited thermals in autonomous cross-country soaring.