Standoff tracking of an unknown object with only distance measurements

In this paper, a guidance algorithm is proposed to solve the problem of standoff tracking control of unknown objects in a GPS-denied environment. Unlike most existing algorithms, the proposed algorithm uses only distance measurements between the unmanned aerial vehicle (UAV) and the object. Algorithm construction is comprised of two steps. The first is to devise a guidance algorithm to drive the UAV to circle around the object assuming that lateral deviation distance measurement and lateral deviation rate measurement are available. The second is to replace the actual measured rate with that estimated by a fixed-time sliding-mode observer. The observer utilizes the lateral deviation distance allowing the UAV to accomplish the tracking mission using only distance measurements. Numerical and hardware-in-the-loop (HIL) simulation results verify the effectiveness of the proposed algorithm, regardless of whether the object is stationary or moving.