Optical Turbulence Measurements and Models for Mount John University Observatory

摘要

Abstract: Site measurements were collected at Mount John University Observatory in 2005 and 2007 usingna purpose-built scintillation detection and ranging system. CNn2n(h) profiling indicates a weak layer located atn12–14 km above sea level and strong low altitude turbulence extending up to 5 km. During calm weathernconditions, an additional layer was detected at 6–8 kmabove sea level. V(h) profiling suggests that tropopausenlayer velocities are nominally 12–30msn1n, and near-ground velocities range between 2 and 20msn1n,ndependent on weather. Little seasonal variation was detected in either CNn2n(h) and V(h) profiles. The averagencoherence length, r0, was found to be 7 1 cm for the full profile at a wavelength of 589 nm. The averagenisoplanatic angle, y0, was 1.0 0.1 arcsec. The mean turbulence altitude, h0, was found to be 2.0 0.7 kmnabove sea level.No average in theGreenwood frequency, fG, could be established due to the gaps present in thenV(h) profiles obtained. A modified Hufnagel-Valley model was developed to describe the CNn2n(h) profiles atnMount John, which estimates r0 at 6 cmand y0 at 0.9 arcsec. A series of V(h)models were developed, based onnthe Greenwood wind model with an additional peak located at low altitudes. Using the CNn2n(h) model and thensuggested V(h) model for moderate ground wind speeds, fG is estimated at 79Hz.