Abstract
A series of experiments studying the characteristics of the effect of turbulence in the atmosphere on the transmission near the ground of visible and near infrared radiation is described. A modulation index which measures the severity of the effect is defined as the normalized mean-square value of the fluctuation of the intensity of the detected radiation. This modulation index and the frequency composition of the fluctuations were measured and their dependence on the diameter of the entrance aperture of the radiometer-receiver were investigated. It was found that the modulation index varies inversely as the diameter, and that the relative frequency composition could be described by an equation of the form: constant/[fa(1 + f/fc)b−a], where f is the frequency and a, b, and fc depend primarily on the size of the entrance aperture. The significance of modulation index, aperture diameter, a, b, and fc are discussed.
© 1965 Optical Society of America
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