Experimental evidence of the effects of non-Kolmogorov turbulence and anisotropy of turbulence

19 July 1999 Experimental evidence of the effects of non-Kolmogorov turbulence and anisotropy of turbulence

Mikhail S. Belen'kii, Stephen J. Karis, Christina L. Osmon, James M. Brown II, Robert Q. Fugate

Author Affiliations +

Proceedings Volume 3749, 18th Congress of the International Commission for Optics; (1999) https://doi.org/10.1117/12.354860
Event: ICO XVIII 18th Congress of the International Commission for Optics, 1999, San Francisco, CA, United States

Abstract

We have observed experimental evidence of the effects of non-Kolmogorov turbulence (NKT) on wavefront tilt. In addition, we have observed the anisotropy of the horizontal and vertical tilt components caused by the anisotropy of turbulence near the telescope. We developed an experimental method, which allowed us to eliminate telescope vibration and isolate the atmospheric tilt from the star Polaris. The spatial and temporal statistics of the wavefront tilt were determined by using aperture masks having diameters in the range from 0.1 m up to 3.5 m. The measured dependencies of the tilt variance on the aperture diameter deviate from the prediction based on the Kolmogorov model. These dependencies have a knee, where the tilt variance approaches a constant level determined by NKT. Anisotropy was observed when comparing the X and Y components of wavefront tilt. On average the horizontal outer scale of turbulence estimated from the tilt statistics is larger than the vertical one by a factor of 2-3. Local topographical features and the telescope dome affect the outer scale with the result that the outer scale measured at the 1 .5 m telescope is smaller than that at the 3 .5 m telescope. The tilt power spectra have a ç2/3 andf"3 behavior in the intermediate and high frequency range, respectively, which is predicted by the Kolmogorov model. In the low frequency range, the spectra do not obey the prediction of existing theoretical models. In this range the power spectra of the horizontal tilt exceed that for vertical tilt as a consequence of anisotropy of turbulence. The tilt temporal correlation scale increases with increasing aperture size. For the large apertures the tilt correlation scale is ofthe order of a few seconds.

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Mikhail S. Belen'kii, Stephen J. Karis, Christina L. Osmon, James M. Brown II, and Robert Q. Fugate "Experimental evidence of the effects of non-Kolmogorov turbulence and anisotropy of turbulence", Proc. SPIE 3749, 18th Congress of the International Commission for Optics, (19 July 1999); https://doi.org/10.1117/12.354860

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