Distributed Kalman filtering compared to Fourier domain preconditioned conjugate gradient for laser guide star tomography on extremely large telescopes

This paper discusses the performance and cost of two computationally efficient Fourier-based tomographic wavefront reconstruction algorithms for wide-field laser guide star (LGS) adaptive optics (AO). The first algorithm is the iterative Fourier domain preconditioned conjugate gradient (FDPCG) algorithm developed by Yang et al. [Appl. Opt. 45, 5281 (2006)], combined with pseudo-open-loop control (POLC). FDPCG’s computational cost is proportional to N log(N), where N denotes the dimensionality of the tomography problem. The second algorithm is the distributed Kalman filter (DKF) developed by Massioni et al. [J. Opt. Soc. Am. A 28, 2298 (2011)], which is a noniterative spatially invariant controller. When implemented in the Fourier domain, DKF’s cost is also proportional to N log(N). Both algorithms are capable of estimating spatial frequency components of the residual phase beyond the wavefront sensor (WFS) cutoff frequency thanks to regularization, thereby reducing WFS spatial aliasing at the expense of more computations. We present performance and cost analyses for the LGS multiconjugate AO system under design for the Thirty Meter Telescope, as well as DKF’s sensitivity to uncertainties in wind profile prior information. We found that, provided the wind profile is known to better than 10% wind speed accuracy and 20 deg wind direction accuracy, DKF, despite its spatial invariance assumptions, delivers a significantly reduced wavefront error compared to the static FDPCG minimum variance estimator combined with POLC. Due to its nonsequential nature and high degree of parallelism, DKF is particularly well suited for real-time implementation on inexpensive off-the-shelf graphics processing units

SAXO+ upgrade : second stage AO system end-to-end numerical simulations

SAXO+ is a proposed upgrade to SAXO, the AO system of the SPHERE instrument on the ESO Very Large Telescope. It will improve the capabilities of the instrument for the detection and characterization of young giant planets. It includes a second stage adaptive optics system composed of a dedicated near-infrared wavefront sensor and a deformable mirror. This second stage will remove the residual wavefront errors left by the current primary AO loop (SAXO). This paper focuses on the numerical simulations of the second stage (SAXO+) and concludes on the impact of the main AO parameters used to build the design strategy. Using an end-to-end AO simulation tool (COMPASS), we investigate the impact of several parameters on the performance of the AO system. We measure the performance in minimizing the star residuals in the coronagraphic image. The parameters that we study are : the second stage frequency, the photon flux on each WFS, the first stage gain and the DM number of actuators of the second stage. We show that the performance is improved by a factor 10 with respect to the current AO system (SAXO). The optimal second stage frequency is between 1 and 2 kHz under good observing conditions. In a red star case, the best SAXO+ performance is achieved with a low first stage gain of 0.05, which reduces the first stage rejection.Comment: 10 pages, 8 figures. Submitted to AO4ELT7 conference proceeding

Multi-core fibre-fed integral-field unit (MCIFU):Overview and first-light

The Multi-Core Integral-Field Unit (MCIFU) is a new diffraction-limited near-infrared integral-field unit for exoplanet atmosphere characterization with extreme adaptive optics (xAO) instruments. It has been developed as an experimental pathfinder for spectroscopic upgrades for SPHERE+/VLT and other xAO systems. The wavelength range covers 1.0 um to 1.6um at a resolving power around 5000 for 73 points on-sky. The MCIFU uses novel astrophotonic components to make this very compact and robust spectrograph. We performed the first successful on-sky test with CANARY at the 4.2 meter William Herschel Telescope in July 2019, where observed standard stars and several stellar binaries. An improved version of the MCIFU will be used with MagAO-X, the new extreme adaptive optics system at the 6.5 meter Magellan Clay telescope in Chile. We will show and discuss the first-light performance and operations of the MCIFU at CANARY and discuss the integration of the MCIFU with MagAO-X.</p

Conception de lois de commande à hautes performances pour l'optique adaptative des grands / très grands télescopes

L optique adaptative (OA) permet de corriger les effets induits par la turbulence atmosphérique, qui dégradent la résolution des télescopes et donc la qualité des images. Introduits dans les années 1990, les systèmes d OA deviennent désormais tomographiques, permettant l analyse du volume turbulent pour une correction à grand champ. Ceci s accompagne d une forte augmentation de la complexité des OA des futurs grands télescopes. Les nouveaux concepts d OA souvent à grands nombres de degrés de liberté (GNDL) requièrent des lois de commande innovantes respectant les contraintes temps réel. Plusieurs aspects originaux sont abordés. Pour les GNDL, le point d'entrée est le choix de la base de représentation de la phase. Deux voies sont explorées : avec une formulation zonale, des méthodes Fourier sont étudiées pour la reconstruction statique de front d'onde ; une nouvelle stratégie combinant méthodes Fourier et méthodes itératives est développée pour adapter la commande optimale linéaire quadratique gaussienne (LQG) aux GNDL. On traite ensuite le problème des dynamiques temporelles des grands miroirs déformables. Pour des dynamiques linéaires, la commande optimale minimisant la variance résiduelle est obtenue comme solution d un problème LQG à temps discret. Ceci permet aussi de quantifier la dégradation de performances pour des commandes sous-optimales. Cette approche est appliquée à la commande des miroirs de basculement destinés aux grands télescopes. On montre que négliger la dynamique conduit à une dégradation significative des performances. Une autre application est traitée: la coordination d un miroir lent et d un miroir rapide (concept woofer-tweeter).Adaptive optics (AO) enables to correct the effects induced by atmospheric turbulence, which affect telescopes resolution and hence image quality. Introduced in the 1990s, AO systems become tomographic, allowing to analyze turbulence in volume in order to achieve wide-field correction. For future large telescopes, this goes together with a sharp increase in complexity. New AO concepts, often exhibiting large number of degrees of freedom (LNDF), require innovative control laws compatible with real-time constraints. Several original aspects are addressed. For LNDFs, the entry point is the selection of a basis for the turbulent phase. Two directions are explored: with a zonal formulation, Fourier methods for static wavefront reconstruction are investigated; a new strategy combining Fourier and iterative methods is developed to adapt optimal Linear Quadratic Gaussian (LQG) control to LNDFs. The issue of large deformable mirror s temporal dynamics is addressed. For linear dynamics, the optimal control minimizing residual variance is obtained as the solution of a discrete-time LQG problem. This also enables to quantify the degradation in performance with suboptimal controllers. This approach is applied to the control of tip-tilt mirrors developed for large telescopes. It is shown that neglecting dynamics results in significant performance degradation. Another application is dealt with: the coordination of slow and fast mirrors (woofer-tweeter concept).PARIS13-BU Sciences (930792102) / SudocSudocFranceF

Delay-Based Non-linear Observers for Congestion Control in Communication Networks

International audienceThe purpose of this contribution is to investigate the construction and use of delay-based observers in communication networks, starting from a state-space model of an elementary network configuration. This work is a step towards the design of a source-rate congestion and delay control algorithm adapted to applications with real-time constraints, such as video streaming. Our ultimate aim is to design an “end to end” control scheme implemented at source level, using only feedback information from the destinations transmitted through the network as part of the general “best effort” data stream, and which could therefore be deployed on essentially every existing network infrastructure, especially those ruled by the Internet Protocol. Obviously, observer-based control structures provide an appropriate conceptual framework to deal with such measurement constraints. In this particular application, we propose to combine a linear state-feedback plus disturbance feedforward control with a non-linear observer of network congestion fed with measurements of source-to-destination transmission delay

Microflore de la litière du sapin Abies alba Mill. : Bactéries et levures

Mise en évidence des bactéries et des levures colonisant les feuilles de la litière. Evolution de cette microflore dans les couches L et F de la litière. Etude des bactéries et des levures isolées, recherche de quelques caractères de ces microorganismes.Faure-Raynaud M., Jacob François-Henri. Microflore de la litière du sapin Abies alba Mill. : Bactéries et levures. In: Bulletin mensuel de la Société linnéenne de Lyon, 47ᵉ année, n°7, septembre 1978. pp. 392-404

Simple control of an adaptive optics retinal imaging system using pupil tracker measurements without pupil stabilization

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Réduction de systèmes linéaires à paramètres incertains

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Model order reduction of random parameter-dependent linear systems

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Intrusive Galerkin Projection for Model Order Reduction of Uncertain Linear Dynamic Systems

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