Autonomous airborne wildlife tracking using radio signal strength

In wildlife radio tagging, small radio transmitters attached to animals are located by human operators using directional antennas and analog receivers which provide audio output. The location of the transmitter is determined by listening to the signal and scanning the area while closing in. This procedure can be very tedious, especially in rough terrain. Searching radio tags with autonomous unmanned aerial vehicles (UAVs) offers a number of advantages, including better line-of-sight signal reception, terrain-independence and faster localization. In this paper we continue upon previous work by presenting a received-signal-strength (RSS) sensor implementation based on a modified commercial wildlife tracking receiver that is designed to operate on an autonomous fixed-wing UAV. Furthermore, an extension of the search and tracking framework for multiple targets that are undistinguishable from the sensors´ point of view is proposed. After a brief system overview and a summary of the particle filter based approach, the signal processing theory and realization of the RSS sensor are outlined, including strategies for frequency tracking and receiver gain control. The paper also presents experimental results.