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Proceedings Paper

Fractal iterative method for fast atmospheric tomography on extremely large telescopes
Author(s): Michel Tallon; Isabelle Tallon-Bosc; Clémentine Béchet; Fabien Momey; Marie Fradin; Éric Thiébaut
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Paper Abstract

A challenge of adaptive optics (AO) on Extremely Large Telescopes (ELTs) is to overcome the difficulty of solving a huge number of equations in real time, especially when atmospheric tomography is involved. This is particularly the case for multi-conjugate or multi-objects AO systems. In addition, the quality of the wavefront estimation is crucial to optimize the performances of the future systems in a situation where measurements are missing and noises are correlated. The Fractal Iterative Method has been introduced as a fast iterative algorithm for minimum variance wavefront reconstruction and control on ELTs. This method has been successfully tested on Classical Single Conjugate AO systems on Octopus numerical simulator at ESO. But the minimum variance approach is expected to be mostly useful with atmospheric tomography. We present the first results obtained with FrIM in the context of atmospheric tomography. We recall the principle of the algorithm and we summarize the formalism used for modeling the measurements obtained from laser guide stars that entail spot elongation and tip/tilt indetermination, mixed with low order measurements from natural guide stars. We show the respective effects of tip/tilt indetermination, spot elongation, unseen modes on various configurations, as well as the usefulness of priors and correct noise models in the reconstruction. This analysis is essential for balancing the various errors that combine in a quite complex way and to optimize the configuration of the future AO systems for specific science cases and instrument requirements.

Paper Details

Date Published: 27 July 2010
PDF: 10 pages
Proc. SPIE 7736, Adaptive Optics Systems II, 77360X (27 July 2010); doi: 10.1117/12.858042
Show Author Affiliations
Michel Tallon, Univ. de Lyon (France)
Observatoire de Lyon, Univ. de Lyon 1 (France)
Ctr. de Recherche Astrophysique de Lyon, CNRS, Ecole Normale Supérieure de Lyon (France)
Isabelle Tallon-Bosc, Univ. de Lyon (France)
Observatoire de Lyon, Univ. de Lyon 1 (France)
Ctr. de Recherche Astrophysique de Lyon, CNRS, Ecole Normale Supérieure de Lyon (France)
Clémentine Béchet, European Organisation for Astronomical Research in the Southern Hemisphere (Germany)
Fabien Momey, Univ. de Lyon (France)
Observatoire de Lyon, Univ. de Lyon 1 (France)
Ctr. de Recherche Astrophysique de Lyon, CNRS, Ecole Normale Supérieure de Lyon (France)
Marie Fradin, Univ. de Lyon (France)
Observatoire de Lyon, Univ. de Lyon 1 (France)
Ctr. de Recherche Astrophysique de Lyon, CNRS, Ecole Normale Supérieure de Lyon (France)
Éric Thiébaut, Univ. de Lyon (France)
Observatoire de Lyon, Univ. de Lyon 1 (France)
Ctr. de Recherche Astrophysique de Lyon, CNRS, Ecole Normale Supérieure de Lyon (France)


Published in SPIE Proceedings Vol. 7736:
Adaptive Optics Systems II
Brent L. Ellerbroek; Michael Hart; Norbert Hubin; Peter L. Wizinowich, Editor(s)

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