19 October 2016 Characterization of optical turbulence at the GREGOR solar telescope: temporal and local behavior and its influence on the solar observations
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Abstract
Local atmospheric turbulence at the telescope level is regarded as a major reason for affecting the performance of the adaptive optics systems using wavelengths in the visible and infrared for solar observations. During the day the air masses around the telescope dome are influenced by flow distortions. Additionally heating of the infrastructure close to telescope causes thermal turbulence. Thereby optical turbulence is produced and leads to quality changes in the local seeing throughout the day. Image degradation will be yielded affecting the performance of adaptive optical systems. The spatial resolution of the solar observations will be reduced. For this study measurements of the optical turbulence, represented by the structure function parameter of the refractive index Cn2 were performed on several locations at the GREGOR telescope at the Teide observatory at Tenerife at the Canary Islands / Spain. Since September 2012 measurements of Cn2 were carried out between the towers of the Vacuum Tower Telescope (VTT) and of GREGOR with a laser-scintillometer. The horizontal distance of the measurement path was about 75 m. Additional from May 2015 up to March 2016 the optical turbulence was determined at three additional locations close to the solar telescope GREGOR. The optical turbulence is derived from sonic anemometer measurements. Time series of the sonic temperature are analyzed and compared to the direct measurements of the laser scintillometer. Meteorological conditions are investigated, especially the influence of the wind direction. Turbulence of upper atmospheric layers is not regarded. The measured local turbulence is compared to the system performance of the GREGOR telescopes. It appears that the mountain ridge effects on turbulence are more relevant than any local causes of seeing close to the telescope. Results of these analyses and comparison of nearly one year of measurements are presented and discussed.
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D. Sprung, D. Sprung, E. Sucher, E. Sucher, K. Stein, K. Stein, O. von der Lühe, O. von der Lühe, Th. Berkefeld, Th. Berkefeld, } "Characterization of optical turbulence at the GREGOR solar telescope: temporal and local behavior and its influence on the solar observations", Proc. SPIE 10002, Optics in Atmospheric Propagation and Adaptive Systems XIX, 1000205 (19 October 2016); doi: 10.1117/12.2245479; https://doi.org/10.1117/12.2245479
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