3D mapping of optical turbulence using an atmospheric numerical model

Abstract

Abstract. These last years have seen the development of many devices to measure and monitor some atmospheric parameters characterizing the image degradation at the telescope focus. Many uncertainties about the possibility to forecast such parameters are real although this skill is fundamental for site testing, flexible scheduling and optimization of the performance of both interferometry and adaptive optics. We present our atmospheric numerical model, conceived to provide 3D maps of the classic meteorological parameters P , T and V , and also 3D maps of the C 2 N optical turbulent profiles. Knowing the wind V and the C 2 N profiles, the following integrated parameters are coded: seeing ε, coherence wavefront time τ AO , isoplanatic angle θ AO , scintillation rate σ 2 I and spatial coherence outer scale L 0 .The ability of the model to produce a 3D map of optical turbulence in the vicinity of a telescope and the effects of horizontal grid size are discussed. We demonstrate, for the same night, the global coherence of the different simulation outputs. Here we consider the use that this model could have in ground-based astronomy and we describe how it could be used to give a real forecast of the optical turbulence.

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

“…The good sensitivity of the Meso-Nh model in reconstructing 3D maps of C 2 N is now supported by many studies (Masciadri et al 1999a;Masciadri et al 1999b;Masciadri et al 2001b). It is time to apply the numerical technique to a concrete problem in the context of 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.…”

Improvements in the optical turbulence parameterization for 3D simulations in a region around a telescope

“…So, in order not to exceed the available memory size for the computer runs, we have to find a numerical compromise that limits the maximum number of grid points in our atmospheric model and that describes, in the best way, the phenomenon that we want to describe: the optical turbulence. Previous studies (Masciadri et al 1999a) showed that a good solution is to take a horizontal resolution of about 500 m extended Send offprint requests to: E. Masciadri, e-mail: elena@astroscu.unam.mx over a surface of 60 × 60 km. In the vertical axis we have the first grid point at a height of 50 m, a variable increasing grid size in the first kilometer above the ground and then a constant size of about 600 m until the end of the troposphere (20 km).…”

“…In preceding papers we have presented comparisons between simulated and measured C 2 N profiles above two of the best astronomical sites: Cerro Paranal (Chile) (Masciadri et al 1999a;Masciadri et al 1999b) and Roque de los Muchachos (Canary Islands) (Masciadri et al 2001a). These works aimed at validating the atmospheric model Meso-Nh which was conceived to simulate classical atmospheric parameters and was then adapted to simulate optical turbulence (3D maps of C 2 N ).…”

Variational Multiscale based dissipation models for the estimation of atmospheric seeing

“…In [29,30] an atmospheric Meso-Nh numerical model was used to compute atmospheric seeing in an observation site in Cerro Paranal, Chile. Soon after, the same methodology was applied to the simulation of another observation site at the Roque de Los Muchachos, Canary Islands, Spain [31].…”