EDP Sciences
Free Access
Volume 371, Number 1, May III 2001
Page(s) 366 - 377
Section Instruments, observational techniques and data processing
DOI https://doi.org/10.1051/0004-6361:20010279

A&A 371, 366-377 (2001)
DOI: 10.1051/0004-6361:20010279

SCIDAR measurements at Pic du Midi

J.-L. Prieur1, G. Daigne2 and R. Avila3

1  UMR 5572 d'Astrophysique, Observatoire Midi-Pyrénées -Centre National de la Recherche Scientifique, 14 avenue Édouard Belin, 31400 Toulouse, France
2  Observatoire de Bordeaux, BP 89, 33270 Floirac, France
    e-mail: daigne@observ.u-bordeaux.fr
3  Instituto de Astronomía UNAM, Campus Morelia, A.P. 72-3 (Xangari), 58089 Morelia Michoacán, México
    e-mail: r.avila@astrosmo.unam.mx

(Received 2 January 2001 / Accepted 14 February 2001 )

We present SCIDAR measurements made at the Pic du Midi Observatory with PISCO. A series of vertical profiles of the refractive-index structure constant $C_{\rm N}^2(h)$ was obtained with the observations of the binary stars $\gamma$ Del and $\gamma$ Ari, with 30 second time sampling. In the free atmosphere, the turbulence was dominated by the contribution of a few well-separated atmospheric layers at altitudes in the range 8-20 km, with significant changes within a few minutes. We describe a new method based on the CLEAN algorithm applied on the 2-D covariance function of the irradiance fluctuations in the pupil plane and compare it with the widely-used Maximum Entropy Method applied on a slice of this 2-D function. Our method is much less sensitive to the noise. Vertical profiles of the wind velocity and direction were obtained with an automatic procedure working on the mean cross-correlation function of consecutive frames. Furthermore, we validate a model for the SCIDAR detectivity threshold in terms of distance to the turbulent layers.

Key words: atmospheric effects -- site testing -- turbulence -- methods: data analysis -- techniques: image processing

Offprint request: J.-L. Prieur, jean-louis.prieur@obs-mip.fr

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