On the comparison between MASS and G-SCIDAR techniques

The Multi Aperture Scintillation Sensor (MASS) and the Generalized-Scintillation Detection and Ranging (Generalized SCIDAR) are two instruments conceived to measure the optical turbulence (OT) vertical distribution on the whole troposphere and low stratosphere (~ 20 km) widely used in the astronomical context. In this paper we perform a detailed analysis/comparison of measurements provided by the two instruments and taken during the extended site testing campaign carried out on 2007 at Cerro Paranal and promoted by the European Southern Observatory (ESO). The main and final goal of the study is to provide a detailed estimation of the measurements reliability i.e dispersion of turbulence measurements done by the two instruments at different heights above the ground. This information is directly related to our ability in estimating the absolute value of the turbulence stratification. To better analyse the uncertainties between the MASS and the GS we took advantage of the availability of measurements taken during the same campaign by a third independent instrument (DIMM - Differential Imaging Motion Monitor) measuring the integrated turbulence extended on the whole 20 km. Such a cross-check comparison permitted us to define the reliability of the instruments and their measurements, their limits and the contexts in which their use can present some risk.

MOSE: optical turbulence and atmospherical parameters operational forecast at ESO ground-based sites. I: Overview and atmospherical parameters vertical stratification on [0-20] km

We present the overview of the MOSE project (MOdeling ESO Sites) aiming at proving the feasibility of the forecast of the classical atmospherical parameters (wind speed intensity and direction, temperature, relative humidity) and the optical turbulence OT (CN2 profiles and the most relevant integrated astro-climatic parameters derived from the CN2: the seeing, the isoplanatic angle, the wavefront coherence time) above the two ESO ground-based sites of Cerro Paranal and Cerro Armazones. The final outcome of the study is to investigate the opportunity to implement an automatic system for the forecast of these parameters at these sites. In this paper we present results related to the Meso-Nh model ability in reconstructing the vertical stratification of the atmospherical parameters along the 20 km above the ground. The very satisfactory performances shown by the model in reconstructing most of these parameters (and in particular the wind speed) put this tool of investigation as the most suitable to be used in astronomical observatories to support AO facilities and to calculate the temporal evolution of the wind speed and the wavefront coherence time at whatever temporal sampling. The further great advantage of this solution is that such estimates can be available in advance (order of some hours) with respect to the time of interest

Optical Turbulence above the Internal Antarctic Plateau

The internal antarctic plateau revealed in the last years to be a site with interesting potentialities for the astronomical applications due to the extreme dryness and low temperatures, the typical high altitude of the plateau, the weak level of turbulence in the free atmosphere down to a just few tens of meters from the ground and the thin optical turbulence layer developed at the ground. The main goal of a site testing assessment above the internal antarctic plateau is to characterize the site (optical turbulence and classical meteorological parameters) and to quantify which is the gain we might obtain with respect to equivalent astronomical observations done above mid-latitude sites to support plans for future astronomical facilities. Our group is involved, since a few years, in studies related to the assessment of this site for astronomical applications that include the characterization of the meteorological parameters and optical turbulence provided by general circulation models as well as mesoscale atmospherical models and the quantification of the performances of Adaptive Optics (AO) systems. In this talk I will draw the status of art of this site assessment putting our studies in the context of the wide international site testing activity that has been done in Antarctica. I will focus on the site assessment relevant for astronomical applications to be done in the visible up to the near infrared ranges, i.e. those ranges for which the optical turbulence represents a perturbing element for the quality of the images and the AO techniques an efficient tool to correct these wavefront perturbations.