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Theses

Assessing time scales of atmospheric turbulence at observatory
sites

Abstract : The research brought together in this thesis is concerned with the
distortion of astronomical observations due to atmospheric
fluctuations. These fluctuations are especially critical for the
technique of interferometry whose potential is here exemplified by
the study of delta Velorum. The focus of the research is,
accordingly, on improved methods to assess the changing viewing
conditions at existing observatories, as well as to determine the
suitability of potential observatory sites.

Site-testing and site-monitoring missions are usually directed at the
assessment of the Fried parameter with instruments such as the
Differential Image Motion Monitor, DIMM. An estimation of the
coherence time requires then, in addition, wind-speed measurements by
weather stations. A more refined evaluation is obtained with
instruments such as the Multi Aperture Scintillation Sensor, MASS,
that measure the altitude profiles of the index structure constant,
Cn^2, and the wind speed with a resolution of about 500m, and infer
the coherence time from the integrated turbulence profiles. The main
error in the estimated coherence time results from the turbulence
below 500m altitude not being accounted for.

To avoid these complexities, we suggest the direct measurement of a
quantity proportional to the coherence time. The variance of the
defocus velocity is a suitable option, because it can be evaluated
through fast and continuous sampling of the atmospheric defocus
coefficient. The concept of a Fast Defocus Monitor, FADE, an
instrument using a small telescope, some simple optics and a fast
camera is described, and first measurements are presented.

The final aim is to use FADE for site monitoring and site testing
campaigns. A particularly challenging and interesting project will be
to monitor the coherence time at DomeC.
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https://tel.archives-ouvertes.fr/tel-00171277
Contributor : Aglae Kellerer <>
Submitted on : Wednesday, September 12, 2007 - 10:41:59 AM
Last modification on : Wednesday, September 23, 2020 - 4:38:06 AM
Long-term archiving on: : Friday, April 9, 2010 - 1:56:33 AM

Identifiers

  • HAL Id : tel-00171277, version 1

Citation

Aglae Kellerer. Assessing time scales of atmospheric turbulence at observatory
sites. Astrophysics [astro-ph]. Université Paris-Diderot - Paris VII, 2007. English. ⟨tel-00171277⟩

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