6 August 2010 Support for site testing of the European Extremely Large Telescope: precipitable water vapor over La Silla
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Abstract
The European Southern Observatory (ESO), the Institute for Space Imaging Science (ISIS) and the AstroMeteorology group at the Universidad de Valparaiso collaborated on a project to understand the precipitable water vapour (PWV) over the La Silla Paranal Observatory. Both La Silla and Paranal were studied with the goal of using them as reference sites to evaluate potential E-ELT sites. As ground-based infrared astronomy matures, our understanding of the atmospheric conditions over the observatories becomes paramount, specifically water vapour since it is the principle source of atmospheric opacity at infrared wavelengths. Several years of archival optical spectra (FEROS) have been analysed to reconstruct the PWV history above La Silla using an atmospheric radiative transfer model (BTRAM) developed by ISIS. In order to better understand the systematics involved, a dedicated atmospheric water vapour measurement campaign was conducted in May 2009 in close collaboration with Las Campanas observatory and the GMT site testing team. Several methods of determining the water column were employed, including radiosonde launches, continuous measurements by infrared radiometers (IRMA), a compact echelle spectrograph (BACHES) and several high-resolution optical echelle spectrographs (FEROS, HARPS and MIKE). All available observations were compared to concurrent satellite estimates of water vapour in an attempt to ground-truth the satellite data. We present a comparison of the methods used, and results from the archival study and measurement campaign. A mean PWV of 3.4 ± 2.4 mm is found for La Silla using FEROS data covering the period 2005-2009. Important lessons on the strengths and limitations of satellite data are presented. The value of a stand-alone high time resolution PWV monitor has been demonstrated in the context of parallel observations from Las Campanas and La Silla.
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Richard R. Querel, Richard R. Querel, Florian Kerber, Florian Kerber, Gaspare Lo Curto, Gaspare Lo Curto, Joanna E. Thomas-Osip, Joanna E. Thomas-Osip, Gabriel Prieto, Gabriel Prieto, Arlette Chacón, Arlette Chacón, Omar Cuevas, Omar Cuevas, Diana Pozo, Diana Pozo, Julio Marín, Julio Marín, David A. Naylor, David A. Naylor, Michel Curé, Michel Curé, Marc S. Sarazin, Marc S. Sarazin, Carlos Guirao, Carlos Guirao, Gerardo Avila, Gerardo Avila, } "Support for site testing of the European Extremely Large Telescope: precipitable water vapor over La Silla", Proc. SPIE 7733, Ground-based and Airborne Telescopes III, 773349 (6 August 2010); doi: 10.1117/12.856480; https://doi.org/10.1117/12.856480
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