Simultaneous exoplanet detection and instrument aberration retrieval in multispectral coronagraphic imaging

High-contrast imaging for the detection and characterization of exoplanets relies on the instrument's capability to block out the light of the host star. Some current post-processing methods for calibrating out the residual speckles use information redundancy offered by multispectral imaging but do not use any prior information on the origin of these speckles. We investigate whether additional information on the system and image formation process can be used to more finely exploit the multispectral information. We developed an inversion method in a Bayesian framework that is based on an analytical imaging model to estimate both the speckles and the object map. The model links the instrumental aberrations to the speckle pattern in the image focal plane, distinguishing between aberrations upstream and downstream of the coronagraph. We propose and validate several numerical techniques to handle the difficult minimization problems of phase retrieval and achieve a contrast of 10^6 at 0.2 arcsec from simulated images, in the presence of photon noise. This opens up the the possibility of tests on real data where the ultimate performance may override the current techniques if the instrument has good and stable coronagraphic imaging quality. This paves the way for new astrophysical exploitations or even new designs for future instruments

Fast and robust detection of a known pattern in an image

International audienceMany image processing applications require to detect a known pattern buried under noise. While maximum correlation can be implemented efficiently using fast Fourier transforms, detection criteria that are robust to the presence of outliers are typically slower by several orders of magnitude. We derive the general expression of a robust detection criterion based on the theory of locally optimal detectors. The expression of the criterion is attractive because it offers a fast implementation based on correlations. Application of this criterion to Cauchy likelihood gives good detection performance in the presence of outliers, as shown in our numerical experiments. Special attention is given to proper normalization of the criterion in order to account for truncation at the image borders and noise with a non-stationary dispersion

Worldwide Dissemination of the blaOXA-23 Carbapenemase Gene of Acinetobacter baumannii1

Controlling the spread of this gene will be difficult

Estimation des aberrations d'un télescope optique par diversité de phase

Cet article est consacré à l'estimation des aberrations optiques d'un télescope spatial d'observation de la Terre par diversité de phase. Deux estimateurs sont présentés et comparés à l'aide de simulations. Le premier, déjà utilisé dans la littérature, repose sur la recherche conjointe des aberrations et de l'objet observé par maximisation de la vraisemblance généralisée. Le second est un nouvel estimateur que nous proposons, basé sur la recherche des aberrations seules par maximum de vraisemblance

Restauration myope d'images 3D par diversité de phase

Nous présentons une méthode de déconvolution 3D myope pour l'imagerie rétinienne, développée dans un contexte bayésien. Plusieurs contrainte sont utilisées, en particulier une contrainte de support en Z (issu de la technique de diversité de phase), afin de mieux contraindre le problème

The 2010 Interferometric Imaging Beauty Contest

We present the results of the fourth Optical/IR Interferometry Imaging Beauty Contest. The contest consists of blind imaging of test data sets derived from model sources and distributed in the OI-FITS format. The test data consists of spectral data sets on an object "observed" in the infrared with spectral resolution. There were 4 different algorithms competing this time: BSMEM the Bispectrum Maximum Entropy Method by Young, Baron & Buscher; RPR the Recursive Phase Reconstruction by Rengaswamy; SQUEEZE a Markov Chain Monte Carlo algorithm by Baron, Monnier & Kloppenborg; and, WISARD the Weak-phase Interferometric Sample Alternating Reconstruction Device by Vannier & Mugnier. The contest model image, the data delivered to the contestants and the rules are described as well as the results of the image reconstruction obtained by each method. These results are discussed as well as the strengths and limitations of each algorithm.Comment: To be published in SPIE 2010 "Optical and infrared interferometry II

Approximations convexes de critères pour la synthèse de Fourier optique

- La synthèse d'ouverture optique, ou interférométrie optique, permet d'atteindre de très hautes résolutions en couplant des télescopes de diamètres raisonnables. Elle conduit à résoudre un problème d'estimation où le modèle de bruit correspond à un critère d'attache aux données non-convexe. L'étude proposée ici consiste à approcher le mieux possible ce modèle de bruit tout en imposant un critère convexe. Cette approximation a été validée sur simulations puis sur des données expérimentales