An Evaluation of Stereo and Laser-Based Range Sensing for Rotorcraft Unmanned Aerial Vehicle Obstacle Avoidance

We present an evaluation of stereo vision and laser-based range sensing for rotorcraft unmanned aerial vehicle (RUAV) obstacle avoidance. Our focus is on sensors that are suitable for mini-RUAV class vehicles in terms of weight and power consumption. The study is limited to the avoidance of large static obstacles such as trees. We compare two commercially available devices that are representative of the state of the art in two-dimensional scanning laser and stereo-based sensing. Stereo is evaluated with three different focal length lenses to assess the tradeoff between range resolution and field of view (FOV). The devices are evaluated in the context of obstacle avoidance through extensive flight trials with an RUAV. We discuss the merits and limitations of each sensor type, including sensing range, FOV, accuracy, and susceptibility to lighting conditions. We show that the stereo device fitted with 8-mm lenses has a better sensing range and vertical FOV than the laser device; however, it relies on careful calibration and is affected by high-contrast outdoor lighting conditions. The laser has a wider horizontal FOV and is more reliable at detecting obstacles that are within a 20-m range. Overall the laser produced superior obstacle avoidance performance, with a success rate of 84% compared to 42% for 8-mm stereo. (C) 2012 Wiley Periodicals, Inc.