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27 July 2010 The hunt for 100% sky coverage
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Tomographic AO (or Wide Field AO) systems use LGS to build a 3D model of turbulence, but rely on NGS for low order sensing. .To preserve reasonable sky coverage, each photon coming from the NGS to sense Tip Tilt has to be optimally exploited. That means a smart control law, a low detection noise, a concentration of the photons onto a small patch and a wave front sensor concept with favorable noise propagation. In this paper, we describe the system choices that were made during the E-ELT laser tomographic system ATLAS phase A study, in order to get a sky coverage as close as possible to 100%. A correct estimation of the sky coverage is therefore a key issue. We have developped a sky coverage estimation strategy based on a Besan¸con model starfield generation, a star(s) selection tool, and a careful estimation of the residual anisoplanatism (after reconstruction process between the NGSs), noise and temporal contributors. We describe the details of the procedure, and derive the ATLAS expected performance.
© (2010) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Serge Meimon, Thierry Fusco, Yann Clenet, Jean-Marc Conan, François Assémat, and Vincent Michau "The hunt for 100% sky coverage", Proc. SPIE 7736, Adaptive Optics Systems II, 77360Y (27 July 2010);

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