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Proceedings Paper

Low-altitude atmospheric turbulence characteristics at Mt. Wilson Observatory
Author(s): Nicholas Short; Walter Fitelson; David D. Snyder Hale; Charles H. Townes
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Paper Abstract

Previous measurements of atmospheric density fluctuations have shown that a substantial fraction of seeing fluctuations occur within 100 feet of the ground, and that the power spectrum of path length fluctuations through the atmosphere has a somewhat smaller slope than that predicted by the Kolmogorov-Taylor approximation. To provide some possibility of appreciable path-length corrections, the ISI has assembled a system capable of measuring temperature changes at fifteen foot intervals of heights up to 70 feet from the ground. Analysis of temperature measurements made under a variety of conditions confirms previous results concerning the decrease in the magnitude of the fluctuations with altitude near the ground: the rms magnitude of the temperature fluctuations at an elevation of 70 feet is, on average, 52% of the mean rms value at 9 feet. However, these new measurements made at point locations show a power spectrum close to the Kolmogorov-Taylor prediction at frequenices up to 1.0 Hz, for average wind speeds above 2 m/s. In addition, correlation analysis between sensors located at the same elevation but separated by a given distance shows up to 50% correlation out to separations as large as 24 meters with wind speeds of a few meters per second, and indicate that Taylor's approximation applies over spatial distances in the range of 24 - 85 meters, or on timescales as large as ten seconds, and perhaps as large as 14 or 15 seconds. This makes path length corrections possible by temperature measurements at nearby locations.

Paper Details

Date Published: 21 February 2003
PDF: 12 pages
Proc. SPIE 4838, Interferometry for Optical Astronomy II, (21 February 2003); doi: 10.1117/12.456998
Show Author Affiliations
Nicholas Short, Univ. of California/Berkeley, Space Sciences Lab. (United States)
Walter Fitelson, Univ. of California/Berkeley, Space Sciences Lab. (United States)
David D. Snyder Hale, Univ. of California/Berkeley, Space Sciences Lab. (United States)
Charles H. Townes, Univ. of California/Berkeley, Space Sciences Lab. (United States)

Published in SPIE Proceedings Vol. 4838:
Interferometry for Optical Astronomy II
Wesley A. Traub, Editor(s)

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