Sambo, Lara (2011) An iterative method to deconvolve codedmask images. Tesi di Dottorato , Università degli Studi di Ferrara.

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Abstract
Efficent astronomical imaging at energy greater than 20 keV is mainly achieved through modulation, either time (i.e. HXMT) or spatial (i.e. IBIS/INTEGRAL), techniques. Currently, the coded mask technique is widely used with the true spatial intensity distribution reconstructed from the data by the crosscorrelation (CC) method. As the sensitivity of instruments increases, so must the angular resolution in order to avoid problems with source confusion. The IBIS 12’ angular resolution is clearly not sufficient to distinguish all the sources in the crowded field of the Galactic Centre. One possibility to overcome this problem is to change the deconvolution method. The objective of this thesis is to evaluate the real imaging capability of the Direct Demodulation (DD) method. It deconvolves incomplete and noisy data by iteratively solving the image formation equation under physical constraints. With the goal of exploiting the DD technique, in the early of the 1990s the HXMT mission was designed, where the imaging capability is obtained through the temporal modulation of the detected counts by a set of mechanical collimators. To achieve this goal, we developed the LucyRichardson (LR) code to reconstruct directly hardX/soft ray images. It assumes that the data and the noise follow a Poisson distribution and it guarantees the nonnegativity of the restored images. For the moment, any kind of regularization or constraint was implemented in the underlying optimization problem, so this will be illposed yet. Due to the general nature of the DD and the fact that HXMT has still to fly, the IBIS/INTEGRAL data and its PSF were used to check our own code. The pure geometrical PSF considering only the effects due to the photon propagation from the mask to the detector was created. Our CC code implements the same balanced crosscorrelation as the standard software for IBIS/INTEGRAL analysis. The CC deconvolved images are the reference for the image quality obtained with the LR. The great improvement in the theoretical angular resolution and location precision is evident. It is independent on the source position in the total FOV, the iteration number and the source flux. Within the parameters of the simulations used, the LR statistical uncertainty was found to be a factor of 10 smaller than that obtained with the CC. Furthermore, the LR deconvolved images have less fluctuating reconstructed background. The main LR drawback is the flux evaluation of the reconstructed source. It is mainly due to the choice of the correct iteration number. The use of apriori information about the unknown object allows a complete regularization of the problem, so probably solving the problem with the flux estimation. Keywords: Codedmask, Lucy, Richardson, INTEGRAL, IBIS
Tipologia del documento:  Tesi di Dottorato (Tesi di Dottorato) 

Data:  24 Marzo 2011 
Relatore:  Frontera, Filippo  Buchan, Stephen John  Zanghirati, Gaetano 
Coordinatore ciclo:  Frontera, Filippo 
Istituzione:  Università degli Studi di Ferrara 
Dottorato:  XXIII Anno 2008 > FISICA 
Struttura:  Dipartimento > Fisica 
Soggetti:  Area 02  Scienze fisiche > FIS/05 Astronomia e astrofisica 
Parole chiave:  codedmask, Lucy, Richardson, INTEGRAL, IBIS 
Depositato il:  13 Apr 2012 14:06 
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