The aspect of atmospheric turbulence of interest to optical-propagation studies is the variation of refractive index. We demonstrate the application of high-speed temperature sensors to the direct measurement of this variation at optically important scale sizes, as small as a few millimeters. The thermometers, used in pairs with spacings ranging from 3 mm to 1 m, disclose that the turbulence near the ground frequently differs substantially from the Kolmogoroff model, and that the temperature difference does not follow the gaussian probability-distribution function. A model of the turbulent atmosphere containing sharply bounded regions with stronger than average turbulence agrees well with our observations. We also demonstrate the use of a single sensor mounted on an airplane to observe refractive-index variations at heights up to 3 km.
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