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Proceedings Paper

Investigating the effect of atmospheric turbulence on mid-IR data quality with VISIR
Author(s): Mario E. van den Ancker; Daniel Asmus; Christian Hummel; Hans-Ulrich Käufl; Florian Kerber; Alain Smette; Julian Taylor; Konrad Tristram; Jakob Vinther; Burkhard Wolff
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Paper Abstract

A comparison of the FWHM of standard stars observed with VISIR, the mid-IR imager and spectrometer at ESO's VLT, with expectations for the achieved mid-IR Image Quality based on the optical seeing and the wavelength-dependence of atmospheric turbulence, shows that for N-band data (7{12μm), VISIR realizes an image quality about 0.1" worse than expected based on the optical seeing. This difference is large compared to the median N-band image quality of 0.3-0.4" achieved by VISIR. We also note that other mid-IR groundbased imagers show similar image quality in the N-band. We attribute this difference to an under-estimate of the effect of the atmosphere in the mid-IR in the parameters adopted so far for the extrapolation of optical to mid-IR seeing. Adopting an average outer length-scale of the atmospheric turbulence above Paranal L0 = 46 m (instead of the previously used L0 = 23 m) improves the agreement between predicted and achieved image quality in the mid-IR while only having a modest effect on the predicted image quality at shorter wavelengths (although a significant amount of scatter remains, suggesting that l0 may not be constant in time). We therefore advocate adopting L0 = 46 m for the average outer length scale of atmospheric turbulence above Cerro Paranal for real-time scheduling of observations on VLT UT3 (Melipal).

Paper Details

Date Published: 11 July 2016
PDF: 11 pages
Proc. SPIE 9910, Observatory Operations: Strategies, Processes, and Systems VI, 99102T (11 July 2016); doi: 10.1117/12.2233701
Show Author Affiliations
Mario E. van den Ancker, European Southern Observatory (Germany)
Daniel Asmus, European Southern Observatory (Chile)
Christian Hummel, European Southern Observatory (Germany)
Hans-Ulrich Käufl, European Southern Observatory (Germany)
Florian Kerber, European Southern Observatory (Germany)
Alain Smette, European Southern Observatory (Chile)
Julian Taylor, European Southern Observatory (Germany)
Konrad Tristram, European Southern Observatory (Chile)
Jakob Vinther, European Southern Observatory (Germany)
Burkhard Wolff, European Southern Observatory (Germany)

Published in SPIE Proceedings Vol. 9910:
Observatory Operations: Strategies, Processes, and Systems VI
Alison B. Peck; Robert L. Seaman; Chris R. Benn, Editor(s)

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