Guillaume Bouchez

University of Nice-Sophia Antipolis, Nice, Provence-Alpes-Côte d'Azur, France

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Publications (3)4.48 Total impact

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    ABSTRACT: Aims. An experiment was set up at the Concordia station in Antarctica during the winter-over period in 2012 to determine the behaviour of atmospheric optical turbulence in the lower part of the atmospheric boundary layer. The aim of the experiment was to study the influence of turbulence and weather conditions on the quality of astronomical observations. The Concordia station is characterised by the high quality of astronomical images thanks to very low seeing values. The surface layer in the interior of Antarctica during the winter is very stably stratified with the differences of temperature between the surface and the top of the inversion, which reach 20-35 degrees C. In spite of this strong static stability, considerable thermal optically active turbulence sometimes occurs and extends to several tens of metres above the surface, depending on weather conditions. It is important to know the meteorological characteristics that favour good astronomical observations. Methods. The optical measurements of the seeing made by differential image motion monitors installed at two levels of 8 and 20 m were accompanied by observations of turbulence in the lowest one hundred meters. Turbulence was detected and evaluated using a high-resolution sodar developed specially for this purpose. The statistics of some relevant meteorological variables including the long-wave downward radiation, which indicates cloudiness, were determined. Results. Typical patterns of the vertical and temporal structure of turbulence shown by sodar echograms were identified, analysed, and classified. The statistics of the depth of the surface-based turbulent layer and the turbulent optical factor for different height layers are presented together with the seeing statistics. We analysed the dependence of both seeing and integral turbulence intensity within the first 100 m on temperature and wind speed. Conclusions. Seeing and turbulence intensity in the atmospheric boundary layer appear to be correlated. The best values of the seeing (<1 arcsec) are observed when the sodar shows very low turbulence intensity. The main contribution to the image distortion is due to turbulence generated within the lowest 30-50 m near the surface. The presented statistics of the vertical distribution of the atmospheric optical turbulence can be used to determine the optimal location for astronomical instruments.
    Astronomy and Astrophysics 08/2014; 568:A44. DOI:10.1051/0004-6361/201323299 · 4.48 Impact Factor
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    ABSTRACT: The study of the distorting action of the atmospheric turbulence is important to understand the reason of the astronomical seeing variability, and to propose reliable methods to estimate the seeing quality. The influence of the atmospheric surface layer thermal turbulence on distortion of astronomical images is investigated. During a campaign carried out at Concordia station at Dome C, East Antarctica in winter 2012, an experiment was carried out to determine the behaviour and the contribution of the optically-active atmospheric turbulence in the lowest tens meters. The surface layer in the interior of Antarctica during winter is extremely stably stratified with the difference of temperature between the surface and the top of the inversion reaching 30-40 °C. Direct optical measurements of the seeing made by differential image motion monitors (DIMM) at two levels, 8 and 20 m, were made simultaneously with turbulence observations in the near-surface atmospheric layer. The intensity of the thermal turbulence was detected and evaluated using both a specially designed high-resolution sodar, and sonic anemometer measurements. The statistics of some meteorological variables, including long-wave downwelling radiation, characterising the presence of cloudiness are obtained. Typical patterns of the turbulence shown by sodargrams are analysed and classified. The statistics of the heights of the surface-based turbulent layer and of the seeing quality values are presented. A correlation exists between the seeing quality and the intensity of turbulence measured by sodar. Statistics of turbulent optical factor (TOF) for different layers within the surface layer are analysed for the total period and for clear sky conditions to give recommendations on how to choose an optimal height for the installation of the astronomical instrumentation.
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    ABSTRACT: We present long term site testing statistics based on DIMM and GSM data obtained at Dome C, Antarctica. These data have been collected on the bright star Canopus since the end of 2003. We give values of the integrated turbulence parameters in the visible (wavelength 500 nm). The median value we obtained for the seeing are 1.2 arcsec, 2.0 arcsec and 0.8 arcsec at respective elevations of 8m, 3m and 20m above the ground. The isoplanatic angle median value is 4.0 arcsec and the median outer scale is 7.5m. We found that both the seeing and the isoplanatic angle exhibit a strong dependence with the season (the seeing is larger in winter while the isoplanatic angle is smaller).
    IAU 288 Astrophysics from Antarctica; 08/2012