Estimation of turbulence characteristic scales in a water cell

Turbulence is one of the key factors responsible for light beam distortions while its propagation through randomly inhomogeneous medium such as the atmosphere. Many common methods of turbulence study are based on the phase or amplitude analyses of the lightwave that have passed through turbulent medium. The significant role of explicit account of the inner and the outer scales in experimental data description is well known. We propose an optical method of turbulence characteristic scales estimation using phase data from Shack-Hartmann sensor obtained of a single laser beam. The method is based on the sequential analysis of normalized correlation functions of Zernike coefficients. It allows the excluding of the structural constant of refractive index value from the analysis and reduces the solution of a two-parameter problem to sequential solution of two single-parameter problems. The method has been applied to analyze the results of measurements performed in a water cell with created turbulence. A horizontal flow was induced to simulate turbulence driftage. It is shown that taking into account the inner scale is necessary for fitting of correlations of the third-order Zernike modes in the experimental error limits for lm/D=0.5 or higher values (lm - the inner scale, D- aperture diameter). Inner scale estimations did not depend on the flow or changes in the temperature difference. We have shown also that taking into account the outer scale is necessary for fitting of experimental correlations of the first-order Zernike modes in the experimental error limits when L0/D<50 (L0 – the outer scale).