Nonlinear Disturbance Observer-Based Standoff Target Tracking for Small Fixed-Wing UAVs

Small fixed-wing UAVs have attracted significant attention thanks to its pragmatic features such as small size, light weight, and low cost. Although many researchers have extensively studied small fixed-wing UAVs, there still remains a room for improvement. One of the improvements is to deal with external disturbances such as wind as small fixed-wing UAVs are susceptible to such external forces. This makes it difficult for UAVs to follow desired paths or moving targets, which may lead to a mission failure. In this paper, we present nonlinear disturbance observer-based standoff tracking guidance for multiple small fixed-wing UAVs in the presence of wind. The nonlinear disturbance observer is used to estimate the wind disturbance and the Lyapunov guidance vector field technique is used to compensate the effect of the wind and follow a ground target. The numerical simulations are carried out and outdoor flight experiments are performed to demonstrate the performance of the proposed approach in a real-world environment.