The analysis of optical propagation through both deterministic and stochastic refractive-index fields may be substantially
simplified if diffraction effects can be neglected. With regard to simplification, it is known that certain geometricaloptics
predictions often agree well with field observations but it is not always clear why this is so. Here, a new
investigation of this issue is presented involving wave optics and geometrical (ray) optics computer simulations of a
beam of visible light propagating through fully turbulent, homogeneous and isotropic refractive-index fields. We
compare the computationally simulated, aperture-averaged angle-of-arrival variances (for aperture diameters ranging
from 0.5 to 13 Fresnel lengths) with theoretical predictions based on the Rytov theory.
Airborne synthetic aperture radar (SAR) imaging systems have reached a degree of accuracy and sophistication that requires the validity of the free-space approximation for radio-wave propagation to be questioned. Based on the thin-lens approximation, a closed-form model for the focal length of a gravity wave-modulated refractive-index interface in the lower troposphere is developed. The model corroborates the suggestion that mesoscale, quasi-deterministic variations of the clear-air radio refractive-index field can cause diffraction patterns on the ground that are consistent with reflectivity artifacts occasionally seen in SAR images, particularly in those collected at long ranges, short wavelengths, and small grazing angles.