Far-Field Intensity Distribution from a Diffracting Aperture in a Turbulent Medium

摘要

Given is an analysis of the effect of atmospheric turbulence in the Fraunhofer region on a near-horizontal beam of finite cross-section near the earth's surface. The far-field intensity distribution at optical frequencies of an initially plane wave from a finite, circular, source aperture is obtained as a function of range and angle for various values of the index structure constant. Describing the turbulence-induced index of refraction fluctuations by the Kolmogorov spectrum, it is found that the time average of the peak radiant intensity in the Fraunhofer region of a finite source aperture decreases with range at a much faster rate than the intensity calculated from absorption and scattering by molecules and particulate matter. Specifically, a beam from a 2-cm aperture at a wavelength of 0.6328 microns in moderate daytime turbulence will have an unscattered range of 5 km. For small values of the inner turbulence scale, the effects of turbulence are dominant over most of the ranges of interest. (Author)