Flight path following guidance for unmanned air vehicles with pan-tilt camera for target observation

An Unmanned Autonomous Vehicle (UAV) is equipped with a nose-mounted camera capable of pan and tilt rotation for the observation of ground targets. The two camera angles are adjusted automatically in order to keep the target in the camera´s field of view. While the camera actuators are fast enough to keep up with vehicle motion, the limited range of the camera angles leads to the target getting out of sight. Therefore, target exposure is affected by wind. Furthermore, the relative position of the sun can lead to glare and image overexposure. While the effect of wind can be improved by commanding a sideslip angle, image overexposure is avoided by keeping the vehicle between sun and target. Thus, it is desirable of define maneuvers that result in maximum target exposure, and provide guidance laws to allow path following for these maneuvers. This paper presents initial results, obtained based on circular and elliptical maneuvers. The results were generated using an accurate non-linear Aerosonde UAV representation and environmental dynamic models. Simulated GPS data was used for the path following guidance. The complete path about the target at constant altitude and airspeed is specified simply by the desired orbital segment and course reversals at the segment boundaries. With camera pan limited to the forward 180°, this can achieve long term observation. A camera with minor ´look-back´ range can provide continuous observation in a maneuver that employs both circular and elliptical segments.