MiRA: image reconstruction for optical interferometry

MiRA is an algorithm for image reconstruction from data provided by optical interferometers. I wrote this algorithm to cope with problems specific to this type of data (sparseness of the measurements, missing of Fourier phase information, etc.) and not solved by existing methods, e.g., developed for radio-astronomy. MiRA won the 2008' Interferometric Imaging Beauty Contest [6] organized by IAU to compare the image synthesis algorithms designed for optical interferometry. An overview of the existing image synthesis algorithms in radio and optical interferometry is provided in [3]; more specifically, MiRA algorithm has been briefly described in [1, 5] and MiRA has been compared to Wisard method in [4].

In a nutshell, MiRA proceeds by direct minimization of a penalized likelihood. This penalty is the sum of two terms: a likelihood term (typically a χ²) which enforces agreement of the model with the data, plus a regularization term to account for priors. The priors are required to lever the many degeneracies due to the sparseness of the spatial frequency sampling. MiRA implements many different regularizations (quadratic or edge-preserving smoothness, total variation, maximum entropy, etc.) and let the user defines his own priors. The likelihood penalty is modular and designed to account for available data of any kind (complex visibilities, powerspectra and/or closure phase). One of the strength of MiRA is that it is purely based on an inverse problem approach and can therefore cope with incomplete data set; for instance, MiRA can build an image without any Fourier phase information.

MiRA is a research tool, it is however free software usable by others (though you need some basic knowledge in optical interferometry). For instance, MiRA has been used to teach image reconstruction in interferometry to the students of the 2008' VLTI Summer School held in Keszthely [3]. MiRA has been used to obtained the results published in a number of scientific journals [2, 7, 8] or conferences.

For now, input data must be in OI-FITS format, extension to other formats (e.g. UV-tables) is on the way. The algorithm is currently modified to achieve true 3-D reconstruction of multi-wavelength images and to account for other interferometers such as ALMA and next generation VLTI instruments (MATIS).

Installation and usage

You can get the last version of MiRA at GitHub

See INSTALL.md for prerequisites and instructions to install MiRA.

See USAGE.md for a short introduction about using MiRA.

References

[1]	E. Thiébaut, P.J.V. Garcia & R. Foy, "Imaging with Amber/VLTI: the case of microjets," Astrophysics and Space Science 286, pp. 171—176, 2003.
[2]	S. Lacour, S. Meimon, É. Thiébaut, G. Perrin, T. Verhoelst, E. Pedretti, P.A. Schuller, L. Mugnier, J. Monnier, J.P. Berger, X. Haubois, A. Poncelet, G. Le Besnerais, K. Eriksson, R. Millan-Gabet, M. Lacasse, & W. Traub, "The limb darkened Arcturus Imaging with the IOTA/IONIC interferometer," Astronomy & Astrophysics 485, 561—570, 2008.
[3]	É. Thiébaut, "Image Reconstruction with Optical Interferometers," in VLTI Summer School: "Astrometry and imaging with the very large telescope interferometer," Keszthely (Hungary), 2008.
[4]	G. Le Besnerais, S. Lacour, L. M. Mugnier, É. Thiébaut, G. Perrin & S. Meimon, "Advanced imaging methods for long-baseline optical interferometry," IEEE Journal of Selected Topics in Signal Processing 2, 767—780, 2008.
[5]	É. Thiébaut, "MiRA: an effective imaging algorithm for optical interferometry," in Astronomical Telescopes and Instrumentation, Proc. SPIE 7013, 70131I (Marseille, France), 2008.
[6]	W. Cotton, J. Monnier, F. Baron, K.-H. Hofmann, S. Kraus, G. Weigelt, S. Rengaswamy, É. Thiébaut, P. Lawson, W. Jaffe, C. Hummel, T. Pauls, H. Schmitt, P. Tuthill & J. Young, "2008 imaging beauty contest," in Astronomical Telescopes and Instrumentation, Proc. SPIE 7013, 70131N (Marseille, France), 2008.
[7]	J.-B. Le Bouquin, S. Lacour, S. Renard, É. Thiébaut & A. Merand, 2009, "Pre-maximum spectro-imaging of the Mira star T Lep with AMBER/VLTI," Astronomy & Astrophysics 496, L1—L4, 2009.
[8]	F. Millour, O. Chesneau, M. B. Fernandes, A. Meilland, G. Mars, C. Benoist, É. Thiébaut, P. Stee, F. Baron, J. Young, A. Carciofi, A. D. de Souza, P. Kervella, R. G. Petrov, F. Vakili, K.-H. Hofmann, P. Bendjoya, L. Waters & G. Weigelt, 2009, "A binary engine fueling HD 87643's complex circumstellar environment using AMBER/VLTI imaging," to be published in Astronomy & Astrophysics.