The effect of scintillating target intensity upon the performance of a pulse-position modulation optical tracker

A prominent noise source encountered in guidance systems based upon daytime optical tracking of targets near the ground is the fluctuation in received target irradiance caused by atmospheric scintillation. The scintillation observed can be reduced somewhat by appropriate optical design; however, the associated signal-processing system must still operate upon a scintillating input signal. Thus, it becomes essential to understand the manner in which scintillation affects the signal-processing performance. If the tracker is of a type which codes the target position into the arrival time of an electrical pulse, the influence of the atmospheric scintillation is made manifest through random variations in both the amplitude of the signal pulse and its shape. The effect of these random variations upon the performance of a specific type of signal-pulse processing is derived in some detail, and calculations of the variance in the measured signal-pulse arrival time are presented. Detection probability and false alarm probability are also presented as functions of the atmospheric scintillation index.