A Bio-Inspired Stereo Vision System for Guidance of Autonomous Aircraft
Richard J. D. Moore · InTech eBooks · 2011
In this section we will briefly discuss the motivations for designing guidance systems for autonomous aircraft and also review some of the techniques used by state-of-the-art systems. Unmanned aerial vehiclesUnmanned aerial vehicles (UAVs) have seen unprecedented levels of growth in both military and civilian application domains since their inception during World War I.So much so, in fact, that the Joint Strike Fighter 1 , which is currently under production, is predicted to be the last manned aircraft produced by the US Armed Forces (Valavanis, 2007).The first pilotless aircraft were intended for use as aerial torpedoes.Today, however, autonomous or semi-autonomous fixed-wing aircraft, airships, or helicopters and vertical take-off and landing (VTOL) rotorcraft are increasingly being used for applications such as surveillance and reconnaissance, mapping and cartography, border patrol, inspection, military and defense missions, search and rescue, law enforcement, fire detection and fighting, agricultural and environmental imaging and monitoring, traffic monitoring, ad hoc communication networks, and extraterrestrial exploration, to name just a few.The reason that UAVs are increasingly being preferred for these roles is that they are able to operate in situations that are either too dangerous, too remote, too dull, or too difficult for manned aircraft (Valavanis, 2007).Typically, today's UAVs are flown remotely by a human pilot.However, with the expanding set of roles there is an increasing need for UAVs to be able to fly with a degree of low-level autonomy, thus freeing up their human controllers to concentrate on high level decisions. Short range navigationModern UAVs are capable of controlling their position and orientation in space accurately using systems such as the Global Positioning System (GPS) and Attitude and Heading Reference Systems (AHRS).This is sufficient when navigating over large distances at high altitude or in controlled airspaces.However, the expanding set of roles for UAVs increasingly calls for them to be able to operate in near-earth environments, and in environments containing 3D structures and obstacles.In such situations, the UAV must know its position in the environment accurately, which can be difficult to obtain using GPS due to occlusions and signal reflections from buildings and other objects.Additionally, the UAV must know a priori the 3D structure of the surrounding environment in order to avoid obstacles.Obviously such a scheme presents severe difficulties in situations where there is no foreknowledge of the 3D structure of the environment, or where this structure can change unpredictably.A more efficient approach would be for the aircraft to monitor its surroundings continuously during flight.The use of active proximity sensors such as ultrasonic or laser range finders, or radar has been considered for this purpose (Scherer et al., 2007).However, such systems can be bulky, expensive, stealth-compromising, high power, and low-bandwidth -limiting their utility for small-scale UAVs.Therefore, there is considerable benefit to be gained by designing guidance systems for UAVs that utilise passive sensing, such as vision. Biological visionThe importance of vision for short range navigation was realised many decades ago.However, it is not until recently that vision-based guidance systems have been able to be 1 Lockheed Martin F-35 Lightning II.