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.