Whole atmospheric-turbulence profiling with generalized scidar

Abstract

Statistical analysis of stellar scintillation on the pupil of a telescope, known as the scidar (scintillation, detection, and ranging) technique, is sensitive only to atmospheric turbulence at altitudes higher than a few kilometers. With the generalized scidar technique, recently proposed and tested under laboratory conditions, one can overcome this limitation by analyzing the scintillation on a plane away from the pupil. We report the first experimental implementation of this technique, to our knowledge, under real atmospheric conditions as a vertical profiler of the refractive-index structure constant C (N)(2) (h). The instrument was adapted to the Nordic Optical Telescope and the William Hershel Telescope at La Palma, Canary Islands. We measure the spatial autocorrelation function of double-star scintillation for different positions of the analysis plane, finding good agreement with theoretical expectations.

Automatic Determination of Wind Profiles with Generalized SCIDAR

“…The SCIDAR technique has been the subject of many papers (e.g., Rocca et al 1974;Vernin & Azouit 1983;Caccia et al 1987;Avila et al 1997;Klückers et al 1998;Prieur et al 2001). Here we present only the guidelines of the method in order to introduce the quantities that are useful for this paper.…”

“…To allow such a determination, Fuchs et al (1998) proposed shifting the (virtual) plane of analysis a few kilometers below the pupil plane. Avila et al (1997) implemented this method on a telescope. This extension of the SCIDAR method is known as generalized SCIDAR (noted here as GS).…”

First evidence of the finite horizontal extent of the optical turbulence layers. Implications for new adaptive optics techniques

“…(1) We compare measured and simulated C 2 N profiles along the same lines of sight. The measured profiles are provided by a Generalized Scidar (Fuchs et al 1998;Avila et al 1997;Avila et al 1998) at the focus of a 2.1 m telescope during a site testing campaign on 16−21 May 2000 in the Observatorio Astronómico Nacional de San Pedro Mártir (Mexico) (31.0441 N, 115.4569 W) and the simulations are provided by the Meso-Nh model (Masciadri et al 1999a;Masciadri et al 1999b In order to give a reliable comparison between measurements and simulations we modified the code so as to give averaged estimations of the optical turbulence calculated over simulations of some hours. We recall that the previous results Masciadri 2001a) were not the result of an average.…”

Multi-instrument measurement campaign at Paranal in 2007

“…Cute-SCIDAR provides the vertical profile of the turbulence energy C 2 n (h) by measuring the scintillation of double stars with a CCD. It is deduced from the spatial autocorrelation functions of the scintillation in two directions, parallel and perpendicular to the double stars separation (Avila et al 1997). The vertical resolution depends on the double star angular separation; for the Cute-SCIDAR it was about 300 m. The integrated optical parameters, seeing and isoplanatic angle, are deduced from the profiles.…”