Distribution Models for Optical Scintillation Due to Atmospheric Turbulence

Abstract : Traditional analyses ot optical scintillation usually invoke the Rytov approximation and the associated assumptions regarding weak phase perturbations throughout the propagation channel. Associated with that approach is the prediction that the statistics of scintillation will be log-normal. This report, which uses the Fresnel propagation function as a basis, challenges many of the standard descriptions of far-field irradiance fluctiiations. A key finding of this study is the importance of the ratio between the transmitted beam diameter and the turbulence coherence diameter. Turbulence-induced beam jitter is found to be a dominant effect when this radius is close to unity, and the relationship between pointing error and scintillation is examined in detail. As a result of this work, models for the mean Strehl, scintillation index, and signal-fade distributions have been developed. Included in this document are a set of detailed comparisons between the new theoretical models and numerical results derived from a beamwave propagation code developed by Lincoln Laboratory.