This seminar addresses the design, error assessment and analysis of a low cost, adaptive, laser range finder based, terrain following system for unmanned aerial vehicles (UAVs). Such a system enables an aircraft to maintain a pre-defined vertical separation (altitude) over the terrain during flight. Terrain following is of interest in military as well as civil applications with first papers on the subject dating back to the sixties of the previous century. Contemporary approaches are based primarily on radar and passive electro-optical sensors (cameras).
In this study a new approach is proposed to surmount the disadvantages of the previous systems and to provide a more compatible, low cost terrain following solution for small UAVs. This system utilizes several, rigidly mounted, laser range finders as its primary measurement device. The measurements obtained from the sensors are used to generate a desired terrain following trajectory for the aircraft. A trajectory tracking algorithm is then incorporated to ensure that the aircraft remains on the desired path, thus satisfying the required altitude. The complexity and performance of the proposed system depends predominantly on the chosen layout of the sensors as well as other design parameters. The study discusses and thoroughly examines the various error factors affecting the system performance. The goal is to develop an analytical error model for the system thus pinpointing the different factors which may cause either improvement or degradation in terrain following performance as well as aid in the system design process. Furthermore, this study demonstrates the effect of the aircraft velocity on the terrain following performance and its relation to the terrain model. Consequently, a terrain model parameter identification scheme is developed and used to determine the preferred aircraft velocity.
The performance of the adaptive terrain following system is evaluated using a three-dimensional Monte-Carlo simulation environment. The simulation results are used to verify the analytical error model as well as to assess the performance over a varying terrain model. The resulting analytical error model quantifies the overall system tracking error, outlines the preferred values for various system parameters, and mainly suggests the optimal pointing angle for the laser range finders.
