Autonomous Landing of a VTOL UAV on a Ship based on Tau Theory

The research on autonomous landing of VTOL UAVs is well established. However, the research on autonomous deck landing using visual methods is relatively not so mature and many of them require the support of ground insfrastructures. In order to reduce such dependencies, a ship landing guidance strategy based on on-board vision is studied. Considering the characteristics of the ship landing issue, we propose a three-phase landing scheme and a decision-making method to ensure landing safety is also studied. For improving the traditional 2D optical-flow method, a 3D velocity vector estimation method using image spherical optical flow is studied. Furthermore, a guidance law based on tau theory is employed by only using the visual information of the line of sight to the target. In this phase, a trajectory tracking controller is applied to generate the velocity commands of the UAV. Finally, the whole algorithm is validated by simulating different wave conditions in Unity3D. Compared with traditional trajectory planning methods, our method does not require complex optimization iterations and can meet both the real-time and accuracy requirements of deck landing.