Theory of measuring the path-averaged inner scale of turbulence by spatial filtering of optical scintillation.

The theory of using an array of receivers as a spatial filter shows that a scintillation variance is sensitive to refractive-index fluctuations the size of the inner scale of turbulence. The competitive scintillation caused by Fresnel zone-sized fluctuations is greatly eliminated even for long propagation paths. This yields a sensitive method for determining the path-averaged inner scale by measuring scintillation variance. The path weighting of the inner-scale determination for plane wave propagation has excellent uniformity along the path. The proposed design resists the impairing effects of saturation of scintillation. The optical measurement of path-averaged inner scale and refractive-index structure parameter can yield estimates of path-averaged turbulence fluxes of momentum and heat in the atmospheric surface layer. The accuracy of such flux estimates is discussed.