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Optical Turbulence Measurements and Models for Mount John University Observatory
Mohr, J. L.; Johnston, R. A.; Cottrell, P. L.
AA(Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch 8020, New Zealand ), AB(ARANZ Scanning Ltd. (ASL), PO Box 3894, Christchurch 8011, New Zealand), AC(Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch 8020, New Zealand)
Publications of the Astronomical Society of Australia, Volume 27, Issue 3, pp. 347-359. (PASA Homepage)
Publication Date:
Astronomy Keywords:
site testing, atmospheric effects, instrumentation: miscellaneous, instrumentation: adaptive optics
Abstract Copyright:
(c) 2010 Astronomical Society of Australia
Bibliographic Code:


Site measurements were collected at Mount John University Observatory in 2005 and 2007 using a purpose-built scintillation detection and ranging system. CN2(h) profiling indicates a weak layer located at 12-14km above sea level and strong low altitude turbulence extending up to 5km. During calm weather conditions, an additional layer was detected at 6-8km above sea level. V(h) profiling suggests that tropopause layer velocities are nominally 12-30ms-1, and near-ground velocities range between 2 and 20ms-1, dependent on weather. Little seasonal variation was detected in either CN2(h) and V(h) profiles. The average coherence length, r0, was found to be 7+/-1cm for the full profile at a wavelength of 589nm. The average isoplanatic angle, theta0, was 1.0+/-0.1arcsec. The mean turbulence altitude, h0, was found to be 2.0+/-0.7km 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 CN2(h) profiles at Mount John, which estimates r0 at 6cm and theta0 at 0.9arcsec. A series of V(h) models were developed, based on the Greenwood wind model with an additional peak located at low altitudes. Using the CN2(h) model and the suggested V(h) model for moderate ground wind speeds, fG is estimated at 79Hz.
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