Simulation of Optical Propagation Through Atmospheric Turbulence Using Two-Dimensional Fourier Transform Techniques.

摘要

Understanding turbulence degradation of electromagnetic wave propagation is essential for efficient operation of laser weapons, target designators, and imaging systems. Random atmospheric refractive index inhomogeneities alter the phase and amplitude of electromagnetic waves. This thesis attempts to model atmospheric turbulence effects by using filtered Gaussian phase screens to represent the random nature of refractive index changes. The simulation uses two-dimensional 512 x 512 fast Fourier transform (FFT) techniques with extended Huygens-Fresnel principles performed on a desk top computer. Simulation verification was accomplished by comparing calculated and theoretical spatial coherence lengths, phi o. Phase only screens produced coherence lengths that were 30 percent larger than theoretical values. By using random phase and amplitude screens, the calculated coherence lengths agreed to within 3 percent of theoretical values. Saturation of the normalized intensity variance, sigma 2/I2, occurred for increasing turbulence using a single phase-amplitude screen. Keywords: Electromagnetic wave scattering; Electromagnetic wave propagation; Optical propagation; Atmospheric turbulence; Coherence length; Huygens-Fresnel theory. (kt)