Untitled Document

Turbulence Profiling in the Canaries Observatories

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Introduction

Although the importance of the experimental knowledge of the vertical structure of the turbulence with good statistical coverage is obvious, has been no an effort continued and systematic of these measures in the observatories, as it has happened to the seeing size. The common monitoring parameters for the turbulence characterization are insufficient for forthcoming MCAO (Multi-Conjugate Adaptive Optics) systems and large telescopes. Site quality traditionally has been characterised by seeing size (zero moment of Cn2), the stability of weather conditions, and useful observing time. Numerous publications give statistical results for sites (e.g. Vernin & Muñoz-Tuñón, 1994 and 1995) such as the Roque de los Muchachos Observatory (ORM, La Palma, Spain). On the other hand, generalized-SCIDAR is perhaps the most contrasted, extended and reliable technique. The reason, probably, is in the absence of an instrument with category of common-user providing profiles of turbulence and wind with quite high height resolution.

Vernin & Roddier (1973) proposed the classical SCIDAR (Scintillation Detection And Ranging) technique, which was developed over a period of several years (Rocca, A., Roddier, F. & Vernin, J., 1974). But this did not allow measuring the turbulence in the lower atmospheric layers above the telescope dome. In order to overcome this shortcoming, Funchs, Tallon, & Vernin (1994 and 1998) proposed the generalized-SCIDAR technique, which has been successfully tested and exploited over the last decade (Ávila, Vernin & Masciadri 1997; Ávila, Vernin & Cuevas 1998; Kluckers et al. 1998). We have developed a new instrument (Fuensalida et al, 2004; Hoegemann et al, 2004), which we call cute-SCIDAR. It is permanently installed at 1m Jacobus Kapteyn Telescope (ORM) and is based on the original generalized-SCIDAR used by the Vernin’s group of Laboratoire Universitaire d’Astrophysique de Nice (LUAN). Recently, we have developed a new version, which has been installed in Paranal Observatory.

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Observations in ORM (2004, 2005)

In order to avoid biased statistical data, we have established to get the measurements in the period of dark nights (around new moon nights) each month. Of this way, besides fixing the statistical sample criterion, we facilitated the SCIDAR observations reducing the background emission. The programming for 2004 was the monitoring throughout one week (dark nights) every month, however technical troubles, bad weather (climatologic conditions out the limits), or overload of work of the team have made to fluctuate the sample. Because the decrease of human resources in the course of 2005, we was reduced to doing less observing nights each month. All resulting profiles were concerned about the statistical calculations, this is, no profile was rejected after data processing.

In the table 1, we resume the statistical coverage of the observations with the number of nights and the profiles each month during 2004 and 2005. We started the measurements with cute-SCIDAR instrument in the JKT on February 2004. During 2004, the average number of profiles per month was 5529 corresponding to more than 997 profiles per night each month (see last row). The total number of nights with measurements was 61 distributed throughout 11 months (5.55 nights/month). In the case of 2005, the average number of profiles per night was 903 in 43 nights throughout 12 months (3.58 nights/month).
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