The level-crossing theory for Gaussian stochastic processes is used to predict the behavior of an optical channel in the turbulent atmosphere. The log-irradiance is assumed to be Gaussian with a known correlation function and the conditional probability that it be below a “fade” at time τ in the future given that it currently exceeds a threshold level is derived. The probability density, two-point conditional density, and the correlation function of the log-irradiance as determined from experimental data collected under weak, moderate, and strong turbulence conditions are presented. The Gaussian assumption is justified on the basis on the measured probability densities but the correlation functions show that the process is not Markov. The measured correlation functions are used to generate the probability of fading as a function of the time delay τ and a measure of the effectiveness of a channel-monitoring system is defined and calculated.
© 1978 Optical Society of America
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