Characterization of Atmospheric Turbulence Over Long Horizontal Paths Using Optical Slope Measurements
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
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Atmospheric turbulence has long been recognized as one of the fundamental factors affecting optical systems operating through the atmosphere. Turbulence over vertical paths has been well characterized, both theoretically and experimentally. Much less is known about turbulence over long, horizontal paths. Perturbations of the wave front phase can be measured using a Hartmann wave front sensor H-WFS. Theoretical expressions for the tilt removed structure function of the H-WFS slope measurements were derived and evaluated using quadrature. These slope structure functions are functions of the phase structure function. The Kolmogorov turbulence model was assumed. Simulated H-WFS slope measurements were generated using an adaptive optics simulation code. The effects of deterministic aberrations on the structure function estimator were illustrated using the simulated slope measurements. Average slope removal was shown to be effective in removing the effects of aberrations. Five H-WFS measurement data sets from the ABLE ACE database were analyzed for homogeneity, isotropy, and fit to theory. The ABLE ACE experiment recorded H-WFS measurements over horizontal paths 20-200 km in length. Results indicate that the turbulence encountered appears to be homogeneous and isotropic and seems to fit the Kolmogorov turbulence model.