The aperture-averaging factor of a circular aperture is derived. This factor gives the effect of a finite receiving aperture on spherical and plane waves in reducing the variance of a fluctuating light signal. Curves of the reduction factor and normalized signal standard deviation as a function of range and receiver aperture diameter are presented and are compared with those which were previously calculated. It is shown that Fried's results agree with the results obtained here only for propagation distances much less than the propagation distance where the average field is down by a factor of the order e to the -1 power. 24 pp. Refs. (KB)
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