Observations of spherical-wave scintillation in strong refractive-index turbulence

Observations of the fine structure of spherical wave intensity scintillation, with concurrent independent measurements of refractive index turbulence and inner scale, made over a 1 km path are presented. Quantitative measurements of the spatial covariance were made by continuously cycling the spacing of two 1-mm diameter detectors, by operating continuously at fixed spacings, and by converting the temporal frequency observed by a small-diameter detector, moving at high speed in a circular pattern, to spatial wavelength. Qualitative information was also obtained through high-speed photographs. Details much smaller than the inner scale, which did not arise from the last few meters of the path, were observed by all techniques.