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Optical turbulence profiling with stereo-SCIDAR for VLT and ELT.

Osborn, J. and Wilson, R. and Sarazin, M. and Butterley, T. and Chacon, A. and Derie, F. and Farley, O. and Haubois, X. and Laidlaw, D. and LeLouarn, M. and Masciadri, E. and Milli, J. and Navarrete, J. and Townson, M. J. (2018) 'Optical turbulence profiling with stereo-SCIDAR for VLT and ELT.', Monthly notices of the Royal Astronomical Society., 478 (1). pp. 825-834.


Knowledge of the Earth’s atmospheric optical turbulence is critical for astronomical instrumentation. Not only does it enable performance verification and optimisation of existing systems but it is required for the design of future instruments. As a minimum this includes integrated astro-atmospheric parameters such as seeing, coherence time and isoplanatic angle, but for more sophisticated systems such as wide field adaptive optics enabled instrumentation the vertical structure of the turbulence is also required. Stereo-SCIDAR is a technique specifically designed to characterise the Earth’s atmospheric turbulence with high altitude resolution and high sensitivity. Together with ESO, Durham University has commissioned a Stereo-SCIDAR instrument at Cerro Paranal, Chile, the site of the Very Large Telescope (VLT), and only 20 km from the site of the future Extremely Large Telescope (ELT). Here we provide results from the first 18 months of operation at ESO Paranal including instrument comparisons and atmospheric statistics. Based on a sample of 83 nights spread over 22 months covering all seasons, we find the median seeing to be 0.64” with 50% of the turbulence confined to an altitude below 2 km and 40% below 600 m. The median coherence time and isoplanatic angle are found as 4.18 ms and 1.75” respectively. A substantial campaign of inter-instrument comparison was also undertaken to assure the validity of the data. The Stereo-SCIDAR profiles (optical turbulence strength and velocity as a function of altitude) have been compared with the Surface-Layer SLODAR, MASS-DIMM and the ECMWF weather forecast model. The correlation coefficients are between 0.61 (isoplanatic angle) and 0.84 (seeing).

Item Type:Article
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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2018 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:17 April 2018
Date deposited:08 May 2018
Date of first online publication:27 April 2018
Date first made open access:No date available

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