European Extremely Large Telescope Site Characterization II: High angular resolution parameters

TL;DR

This study characterizes high angular resolution observational parameters at four potential E-ELT sites using consistent measurement techniques, providing detailed turbulence and atmospheric stability data crucial for telescope performance optimization.

Contribution

It offers a comprehensive comparison of turbulence parameters across four candidate sites using standardized instruments and methods during the E-ELT design phase.

Findings

Quantified seeing conditions and isoplanatic angles for each site.

Analyzed seasonal and nightly variations of turbulence parameters.

Estimated coherence time and 'coherence étendue' from wind profile data.

Abstract

This is the second article of a series devoted to European Extremely Large Telescope (E-ELT) site characterization. In this article we present the main properties of the parameters involved in high angular resolution observations from the data collected in the site testing campaign of the E-ELT during the Design Study (DS) phase. Observations were made in 2008 and 2009, in the four sites selected to shelter the future E-ELT (characterized under the ELT-DS contract): Aklim mountain in Morocco, Observatorio del Roque de los Muchachos (ORM) in Spain, Mac\'on range in Argentina, and Cerro Ventarrones in Chile. The same techniques, instruments and acquisition procedures were taken on each site. A Multiple Aperture Scintillation Sensor (MASS) and a Differential Image Motion Monitor (DIMM) were installed at each site. Global statistics of the integrated seeing, the free atmosphere seeing, the boundary layer seeing and the isoplanatic angle were studied for each site, and the results are presented here. In order to estimate other important parameters such as the coherence time of the wavefront and the overall parameter "coherence \'etendue" additional information of vertical profiles of the wind speed was needed. Data were retrieved from the National Oceanic and Atmospheric Administration (NOAA) archive. Ground wind speed was measured by Automatic Weather Stations (AWS). More aspects of the turbulence parameters such as their seasonal trend, their nightly evolution and their temporal stability were also obtained and analyzed.