Application of Optical Scintillation Measurements to Turbulence Diagnostics*

The irradiance fluctuations of beams which propagate through a turbulent medium can be used to infer the spatial spectrum of the turbulent scatterers. The propagation of Goubau-type beam waves in a random medium is used to show that amplitude fluctuations depend upon the transmitter aperture size, observation distance, and wavelength. Most of the results are presented in terms of a parameter, αL, which is inversely proportional to the Fresnel number, πW02/Lλ. A Monte Carlo numerical procedure is used to obtain the normalized mean-square log-amplitude fluctuation as a function of the inverse Fresnel number for various magnitudes of the turbulence inner scale. The applicability of these procedures to measured turbulence spectra is also discussed.