Trajectory Precision Requirements for Automatic Landing

Requisite to landing an aircraft automatically is the perception of its altitude. This report attempts to resolve the theoretical accuracy of an aircraft´s altitude by standard statistical equations for the propagation of error. Available aircraft trajectory data have been used to determine bandwidth of aircraft trajectories during approach and ``landing.´´ Such data also have been incorporated to establish bandwidth of the noise superimposed by apparent radar target ``wander.´´ A method of removing the noise by optimum filtering techniques is discussed. A means of retrieving the high frequency components of the aircraft trajectory information by inertial equipment is proposed. It is further proposed that similar smoothing techniques be utilized to remove low-frequency drift terms which appear as noise in the in ertial equipment. The two sources of information are subsequently recombined to obtain broadband trajectory coverage having a greatly improved signal-to-noise ratio.