Computer simulation of wave propagation through turbulent media
Davis, Charles A.
Walters, David L.
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This research used Huygens-Fresnel wave optics computer simulations to investigate the effects of high turbulence strength and inner scale on the normalized irradiance variance and coherence length of electromagnetic waves propagating through a turbulent atmosphere. These investigations developed several guidelines for validity of propagation simulations employing a numerical, split-step, Huygens-Fresnel, method, and within these guidelines, considered five types of turbulence spectrum inner scale: (1) zero inner scale, (2) Gaussian inner scale, (3) Hill's and (4) Frehlich's viscous-convective enhancement inner scales, and (5) turbulence spectrum truncation from the discrete grid representation. The simulation results showed that the normalized irradiance variance generally decreased (-30%) below the zero inner scale values in the Rytov regime with increasing inner scale size, but increased monotonically in the saturation regime, and agreed within 2% of the Rytov- Tatarski predictions at low turbulence strengths. The E-field coherence length in a spatially confined beam, with either spherical or plane wave divergence and zero inner scale, followed the Rytov-Tatarski-Fried predictions in the Rytov regime, but departed from the theory in the saturation regime. Increasing inner scale size modified this finite beam behavior by raising the coherence length (up to -50%) in the saturation regime.
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