Development of a vision-based guidance law for tracking a moving target

This paper develops a guidance law for a small unmanned aerial vehicle (UAV) performing vision-based tracking of a target moving on the ground. The target's velocity is unknown, but constant; the relative altitude between the target and the UAV is also assumed to be unknown and constant. This work extends earlier results for which the relative altitude between the target and the UAV was known, for example, by comparing captured images with a geo-referenced database. The problem of estimating the unknown parameters is addressed using an adaptive estimator that uses real-time measurements of the target position in the camera frame, as provided by an image processing algorithm. The parameter estimates are used in the UAV guidance law, with turn rate as the input, where the objective is to maintain a desired horizontal distance between the UAV and the target. Simulations show that the proposed algorithm is effective at tracking a target moving with unknown constant velocity, even with repeated out-of-frame events. A stability proof for the combined estimation and guidance algorithm is provided. The paper also describes the development of a Hardware-in-the-Loop simulation, reflecting a realistic tactical scenario, that is intended to provide further validation in advance of flight tests.