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Vertical Scales of Turbulence at the Mount Wilson ObservatoryThe vertical scales of turbulence at the Mount Wilson Observatory are inferred from data from the University of California at Berkeley Infrared Spatial Interferometer (ISI), by modeling path length fluctuations observed in the interferometric paths to celestial objects and those in instrumental ground-based paths. The correlations between the stellar and ground-based path length fluctuations and the temporal statistics of those fluctuations are modeled on various timescales to constrain the vertical scales. A Kolmogorov-Taylor turbulence model with a finite outer scale was used to simulate ISI data. The simulation also included the white instrumental noise of the interferometer, aperture-filtering effects, and the data analysis algorithms. The simulations suggest that the path delay fluctuations observed in the 1992-1993 ISI data are largely consistent with being generated by refractivity fluctuations at two characteristic vertical scales: one extending to a height of 45 m above the ground, with a wind speed of about 1 m/ s, and another at a much higher altitude, with a wind speed of about 10 m/ s. The height of the lower layer is of the order of the dimensions of trees and other structures near the interferometer, which suggests that these objects, including elements of the interferometer, may play a role in generating the lower layer of turbulence. The modeling indicates that the high- attitude component contributes primarily to short-period (less than 10 s) fluctuations, while the lower component dominates the long-period (up to a few minutes) fluctuations. The lower component turbulent height, along with outer scales of the order of 10 m, suggest that the baseline dependence of long-term interferometric, atmospheric fluctuations should weaken for baselines greater than a few tens of meters. Simulations further show that there is the potential for improving the seeing or astrometric accuracy by about 30%-50% on average, if the path length fluctuations in the lower component are directly calibrated. Statistical and systematic effects induce an error of about 15 m in the estimate of the lower component turbulent altitude.
Document ID
19990070483
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Treuhaft, Robert N.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA United States)
Lowe, Stephen T.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA United States)
Bester, Manfred
(California Univ. Berkeley, CA United States)
Danchi, William C.
(California Univ. Berkeley, CA United States)
Townes, Charles H.
(California Univ. Berkeley, CA United States)
Date Acquired
August 19, 2013
Publication Date
November 1, 1995
Publication Information
Publication: Astrophysical Journal
Publisher: American Astronomical Society
Volume: 453
Subject Category
Meteorology And Climatology
Funding Number(s)
CONTRACT_GRANT: NSF AST-91-19317
CONTRACT_GRANT: N00014-89-J-1583
Distribution Limits
Public
Copyright
Other

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