SCIDAR measurements at Pic du Midi^*

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

Corresponding author: J.-L. Prieur, jean-louis.prieur@obs-mip.fr

Received: 2 January 2001
Accepted: 14 February 2001

Abstract

We present SCIDAR measurements made at the Pic du Midi Observatory with PISCO. A series of vertical profiles of the refractive-index structure constant was obtained with the observations of the binary stars γ Del and γ 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.