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Optical Turbulence Measurements and Models for Mount John University Observatory

Published online by Cambridge University Press:  02 January 2013

J. L. Mohr*
Affiliation:
Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch 8020, New Zealand
R. A. Johnston
Affiliation:
ARANZ Scanning Ltd. (ASL), PO Box 3894, Christchurch 8011, New Zealand
P. L. Cottrell
Affiliation:
Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch 8020, New Zealand
*
CCorresponding author. Email: [email protected]
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Abstract

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Site measurements were collected at Mount John University Observatory in 2005 and 2007 using a purpose-built scintillation detection and ranging system. C2N(h) profiling indicates a weak layer located at 12–14 km above sea level and strong low altitude turbulence extending up to 5 km. During calm weather conditions, an additional layer was detected at 6–8 km above sea level. V(h) profiling suggests that tropopause layer velocities are nominally 12–30m s−1, and near-ground velocities range between 2 and 20m s−1, dependent on weather. Little seasonal variation was detected in either C2N(h) and V(h) profiles. The average coherence length, r0, was found to be 7±1 cm for the full profile at a wavelength of 589 nm. The average isoplanatic angle, θ0, was 1.0±0.1 arcsec. The mean turbulence altitude, , was found to be 2.0±0.7 km above sea level. No average in the Greenwood frequency, fG, could be established due to the gaps present in the V(h) profiles obtained. A modified Hufnagel-Valley model was developed to describe the C2N(h) profiles at Mount John, which estimates r0 at 6 cm and θ0 at 0.9 arcsec. A series of V(h) models were developed, based on the Greenwood wind model with an additional peak located at low altitudes. Using the C2N(h) model and the suggested V(h) model for moderate ground wind speeds, fG is estimated at 79 Hz.

Type
Research Article
Copyright
Copyright © Astronomical Society of Australia 2010

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