Scintillation measurements for large integrated-path turbulence*

Abstract

Scintillation measurements are described for a very-large integrated-path turbulence. Measurements were made with simultaneous, coincident beams at 10.6 μm and 4880 Å over a 6-km uniform path. The experimental results include (i) the (log amplitude) variance at 10.6 μm showed saturation at a level comparable to that for shorter wavelengths; (ii) the variance beyond saturation at 4880 Å decreased for increasing turbulence (C_n²), with an exponent of (−0.48) and no apparent asymptote; (iii) the covariance functions, C_l(r), exhibited the emergence of two scale sizes, as manifested by a rapid initial drop vs $\left(r\right)$, and a residual correlation out to large separations; (iv) a corresponding effect was revealed by the spectra of scintillations; (v) receiver-aperture smoothing at 4880 Å was very poor, owing to the large residual correlation sizes; and (vi) the amplitude statistics at both wavelengths approximated log-normal distributions.