Tracking of marine surface objects from unmanned aerial vehicles with a pan/tilt unit using a thermal camera and optical flow

This paper presents a vision-based tracking system for marine surface objects utilizing images captured in a fixed-wing unmanned aerial vehicle (UAV) with a retractable pan/tilt gimbal. A formula for calculating the North-East velocities of objects detected in the images is derived. The formula utilizes optical flow (OF) and compensates for the UAV and gimbal motions. It can be used together with georeferencing to obtain position and velocity measurements of objects detected in the images. The tracking system is suitable with both infrared and visual spectrum images. A flight experiment has been conducted near the Azores, Portugal in 2015 to gather thermal images with marine surface objects. The tracking system has been evaluated off-line and the results show that a marine vessel can be tracked in the North-East-Down (NED) plane.