Cooperative Motion Planning for Persistent 3D Visual Coverage With Multiple Quadrotor UAVs

In this paper, we address the multiple quadrotor UAVs trajectory planning optimization problem for large-scale, persistent, high-depth visual coverage tasks in three-dimensional (3-D) terrain environment. To minimize the overall energy expenditure of the UAVs for accomplishing a task, we set up an air-to-ground collaborative system which introduces base stations to hold and recharge UAVs. The system is formulated as an integer programming, and solved by a novel hierarchical reinforcement learning trajectory planning algorithm (RL-TP), in which the paths are obtained by reinforcement learning method, and then the trajectories are obtained by Bézier curve method. Both simulation and physical experiments show that RL-TP can effectively improve the efficiency and persistence of aerial visual coverage task. Note to Practitioners—While the multi-rotor UAV has been an important means for field monitoring, it suffers the problem of short battery life a lot. To make it more efficient and persistent, we use multiple UAVs and introduce ground base stations to charge the UAVs. The scenario is formulated as an air-to-ground collaborative system, and the motion planning strategy is to minimize the energy consumption. We propose a hierarchical collaborative coverage reinforcement learning trajectory planning algorithm (RL-TP) to solve it. We carry out both simulation and physical field experiments, and compare RL-TP with other popular methods. The experimental results show that the system is feasible and RL-TP performs well in both time efficiency and energy consumption. In future research, we will introduce unmanned ground vehicles to replace the stationary ground base stations to make the air-to-ground collaborative system more powerful and flexible.