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Authors: M. Bertero, and P. Boccacci
Abstract: The Large Binocular Telescope (LBT), whick will be available in a few years from now, has been designed for high-resolution optical/infrared imaging through coherent cophasing of the two mirrors. The structure of the process of image formation in LBT is similar to that in Computed Tomography (CT) so that it is interesting to investigate the applicability to LBT of image restoration methods developed for CT. A powerful one is the so-called Expectation Maximization (EM), which is also known in the astronomical literature as Lucy-Richardon (LR) method. However slow convergenze is a drawback of this method. In the case of CT an accelerated version, based on ordered subsets of projection data (OS-EM), has been proposed. In this paper we adapt OS-EM to the problem of restoring LBT images and we show that it provides an acceleration by a factor which is roughly equal to the number of indipendent interferometric images of the same object.

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Posted by: admin, on 11/1/2006, in category "2000"
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Authors: M. Bertero, and P. Boccacci
Abstract: A complete axplitation of the imaging properties of the Large Binocular Telescope (LBT) will require a generalization of the restoration methods which apply to the case of a single image. Several different observations must be combined to obtain a high-resolution representation of a given target. The purpose of thi paper is to extend to this problem some of the most used restoration methods, including linear methods such as Tikhonov regularization as well as iterative regularization methods providing positive solution. The proposed methods are implemented and tested on simulated LBT images of diffuse and point-like objects. The results are discussed both from the point of view of the accuracy and from that of the computational efficenty, because LBT images may contain, in principle, up to 10^8 pixels.

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Posted by: admin, on 11/1/2006, in category "2000"
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Authors: S.Correia, A.Richichi
Abstract: We present an experiment of interferometric imaging for the Large Binocular Telescope (LBT), conducted at the 1.5m TIRGO infrared telescope. The raw data were produced by simulating the LBT pupil with a mask on the secondary mirror. Two different conditions of D/r0, where D is the single aperture diameter and r0 the Fried parameter, were simulated by the choice of D; field rotation was simulated by rotating the mask. The data set collected consists of several sequences of short exposure interferograms of one point-like and one binary star in the J-band, for two different D/r0 conditions. We show preliminary results, in particular concerning the fringe contrast loss with integration time. The ability of a Lucy-Richardson based deconvolution algorithm to reconstruct an object from a set of LBT-like interferometric real data was demonstrated on the binary star Leo. The retrieved binary parameter values are compared to catalog values, and a good astrometric agreement is found. Photometric and resolution limitations are also discussed. In a first part, the reconstruction method and preliminary numerical simulations of LBT image restoration using this method are presented.

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Posted by: admin, on 11/1/2006, in category "2000"
Views: this article has been read 7545 times
Authors: S. Correia, M. Carbillet, A. Richichi, M. Bertero, and P. Boccacci
Abstract: In this paper we present simulations of Large Binocular Telescope (LBT) image reconstruction carried out on different types of scientific object. The set of Adaptive Optics-corrected point-spread functions (AO-corrected PSFs) used was generated by means of the Code for Adaptive Optics System (CAOS 2.0). For clarity only one restoration method was applied to the simulated data, namely the extension of the Lucy-Richardson (LR) algorithm, also called ML-EM (Maximum Likelihood - Expectation Maximization). When possible we evaluated the quality of the restorations obtained both by astrometric and photometric analysis. By comparison with results obtained using analytical PSFs, we point out the effect induced by the AO correction on the precision of the retrieved astrometric and photometric parameters or on the morphology of the reconstructed object.

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Posted by: admin, on 11/1/2006, in category "2000"
Views: this article has been read 7566 times
Authors: M.Bertero, P.Boccacci, S.Correia, A.Richichi
Abstract: The Large Binocular Telescope (LBT) has been designed for providing images with high sensitivity and resolution by means of optical/infrared interferometry. It will require specific methods for data reduction since the image of an astronomical object will be obtained from a set of interferometric images corresponding to different orientations of the baseline. In this paper we first stress an interesting analogy between the images of LBT and the projections in Computed tomography (CT). Next we use this analogy for extending to LBT some iterative restoration methods developed for CT, such as ML-EM (Maximum Likelihood -Expectation Maximization), its accelerated version OS-EM (Ordered Subset - Expectation Maximization) and the improved version RAMLA (Row-Action Maximum Likelihood Algorithm). These iterative methods approximate solutions of the Maximum Likelihood problem in the case of Poisson noise. We also consider iterative methods which have been proposed for solving the same problem in the case of Gaussian noise, in particular the Iterative Space Recostruction Algortithm (ISRA) and the Projected Landweber (PL) method. All these methods are implemented and tested by means of same simulated LBT images.

Rating: 14 user(s) have rated this article Average rating: 5.0
Posted by: admin, on 11/1/2006, in category "2000"
Views: this article has been read 7393 times