Artificial turbulence generation alternatives for use in computer and laboratory experiments

摘要

Two methods, the spectral and the covariance, are investigated and compared for generating phase screens for modeling the propagation of light through turbulent atmosphere. The spectral method uses the Kolmogorov spectrum which does not define a spectrum below a specified low spatial frequency cutoff. The difficulties of defining the spectrum below the cutoff and the corresponding difficulties this presents for modeling are discussed. Phase screens are shown using the spectral method and have the correct spectrum. However, the phase screens lose accuracy for truncated low spatial frequencies because of a Fourier transform operation. Phase screens are shown that are produced using the covariance method and Kolmogorov structure function for turbulence in the atmosphere. This method avoids taking a Fourier transform but cannot easily model low spatial frequencies below the cutoff for the Kolmogorov spectrum. We show that because the largest powers are in the low spatial frequencies, according to the Kolmogorov spectrum, that truncating the largest eigenvalues has the effect of reducing the low spatial frequencies. The covariance method takes longer to compute and is the subject of ongoing investigation.