A quadrotor sensor platform

Abstract : The Global Positioning System (GPS) has become the de facto standard for precision navigation for many applications. However, the line-of-sight signals required by the GPS receiver are not always accessible in a cluttered environment, such as mountainous terrain or an urban setting. In addition, the satellite signals operate at a low power level making GPS susceptible to interference and jamming. Scenarios such as these require an alternate means of providing high level accuracy. To that end, the Avionics Engineering Center (AEC) at Ohio University (OU) has begun to investigate the ability of a scanning laser range finder, or LADAR, to augment GPS. One scenario under consideration is that of a small unmanned aerial vehicle (UAV) which has been navigating using GPS but then descends into a city for the next phase of its mission. Inside this "urban canyon," access to the GPS satellite signals is blocked by towering buildings and an alternate means of navigation is required to maintain precise positioning. A tactical grade inertial navigation system (INS) would satisfy the requirement, but the cost is prohibitive for an unmanned system. Instead, a line scanning LADAR updates the vehicle's position and attitude using range data collected from planar surfaces. The quadrotor sensor platform is especially well suited for the scanning LADAR since the vehicle itself can be used to "gimbal" the sensor. In other words, small rolling and pitching motions, either commanded or incidental, will generate multiple LADAR line scans across each flat surface. A minimum of three separate scans is required for each planar surface to obtain a three-dimensional solution, but multiple scans are not possible without some means of gimbaling the LADAR.