9 October 2008 Optical turbulence profiling at Mount John University Observatory
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Abstract
The distortion of images due to atmospheric turbulence is one of the major problems in astronomical imaging. To compensate for turbulence induced aberrations in real-time, it is vital to have an accurate model of turbulence strength, C2N(h), and the average wind velocity, V(h), above a given site. To that end, a bread-board based SCIntillation Detection and Ranging (SCIDAR) system was developed for the Mount John University Observatory (MJUO), located in New Zealand. The system, constructed from commercially available off-the-shelf components, provides the flexibility to capture simultaneous pupil-plane and generalised SCIDAR. This provides a useful tool for the measurement of optical turbulence at sites where the near-ground turbulence is exceptionally strong and masks higher altitude layers. Measurements taken at MJUO, using the purpose-built instrument over the last few years, consistently indicate the presence of very strong near-ground turbulence and at least two high altitude turbulence layers (approximately 6 km and 11km above the site), with an additional layer at 1-3 km when strong ground winds are present. The C2N(h) trends from several months in 2005 and 2007 and the V(h) trends from two months in 2007 are presented. The coherence length, r0, for the full profile was consistently 6-7 cm regardless of season or weather conditions in the months used in this trending. The Greenwood frequency, fG , ranged between 12 and 30 Hz for May and June 2007.
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Judy L. Mohr, Judy L. Mohr, Rachel A. Johnston, Rachel A. Johnston, C. Clare Worley, C. Clare Worley, Peter L. Cottrell, Peter L. Cottrell, "Optical turbulence profiling at Mount John University Observatory", Proc. SPIE 7108, Optics in Atmospheric Propagation and Adaptive Systems XI, 710809 (9 October 2008); doi: 10.1117/12.799756; https://doi.org/10.1117/12.799756
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