Comptes Rendus
The next generation radiotelescopes / Les radiotélescopes du futur
LOFAR calibration and wide-field imaging
Comptes Rendus. Physique, Volume 13 (2012) no. 1, pp. 28-32.

LOFAR is a revolutionary instrument, operating at low frequencies (ν240 MHz). It will drive major breakthroughs in the area of observational cosmology, but its use requires the development of challenging techniques and algorithms. Since its field of view and sensitivity are increased by orders of magnitude as compared to the older generation of instruments, new technical problems have to be addressed. The LOFAR survey team is in charge of commissioning the first LOFAR data produced in the imager mode as part of building the imaging pipeline. We are developing algorithms to tackle the problems associated with calibration (ionosphere, beam, etc.) and wide-field imaging for the achievement of the deep extragalactic surveys. New types of problems arise in that context, and notions such as algorithmic complexity and parallelism become fundamental.

LOFAR est un instrument au design révolutionnaire qui opère à très basses fréquences (10240 MHz) dans un domaine dʼénergie quasiment inexploré. Il est construit presque entièrement en software, et allie réseau phasé et interféromètre. Son utilisation conduira à des avancées scientifiques majeures, mais elle représente un défi technologique considérable. En effet, la sensibilité et le champ de vue de cet instrument étant accru de plusieurs ordres de grandeur par rapport à lʼancienne génération, des phénomènes subtils doivent être considérés. Dʼautre part, les nouvelles technologies utilisées comme les réseaux phasés entraînent des complications de taille. Dans le cadre du groupe de travail « relevés LOFAR » nous développons des procédures dʼétalonnage (ionosphère, lobes de station). Dans le cadre de ces problématiques, de nouvelles difficultés émergent, et les concepts de complexité algorithmique et de parallélisabilité deviennent une base de réflexion.

Published online:
DOI: 10.1016/j.crhy.2011.10.006
Keywords: LOFAR, Interferometry, Calibration, Imaging
Mot clés : LOFAR, Interférométrie, Calibration, Imagerie

Cyril Tasse 1; Ger van Diepen 2; Sebastiaan van der Tol 3; Reinout J. van Weeren 3; Joris E. van Zwieten 3; Fabien Batejat 4; Sanjay Bhatnagar 5; Ilse van Bemmel 2; Laura Bîrzan 3; Annalisa Bonafede 6; John Conway 4; Chiara Ferrari 7; Francesco De Gasperin 8; Kumar Golap 5; George Heald 2; Neal Jackson 9; Giulia Macario 7; John McKean 2; Niruj Mohan 3; Emanuela Orrù 10; Roberto Pizzo 2; David Rafferty 3; Urvashi Rau 5; Huub Röttgering 3; Aleksandar Shulevski 10; on behalf of the LOFAR Collaboration 

1 GEPI, observatoire de Paris-Meudon, 5 place Jules-Janssen, 92190 Meudon, France
2 ASTRON, Postbus 2, 7990 AA Dwingeloo, The Netherlands
3 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
4 Onsala Space Observatory, Chalmers University of Technology, 43992 Onsala, Sweden
5 National Radio Astronomy Observatory, Socorro, NM 87801, USA
6 INAF – Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
7 UNS, CNRS UMR 6202 Cassiopée, observatoire de la Côte dʼAzur, 06300 Nice, France
8 Max-Planck-Institut für Astrophysik, Karl-Schwarzschildstraße 1, 85741 Garching, Germany
9 Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
10 Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
@article{CRPHYS_2012__13_1_28_0,
     author = {Cyril Tasse and Ger van Diepen and Sebastiaan van der Tol and Reinout J. van Weeren and Joris E. van Zwieten and Fabien Batejat and Sanjay Bhatnagar and Ilse van Bemmel and Laura B{\^\i}rzan and Annalisa Bonafede and John Conway and Chiara Ferrari and Francesco De Gasperin and Kumar Golap and George Heald and Neal Jackson and Giulia Macario and John McKean and Niruj Mohan and Emanuela Orr\`u and Roberto Pizzo and David Rafferty and Urvashi Rau and Huub R\"ottgering and Aleksandar Shulevski and on behalf of the LOFAR Collaboration},
     title = {LOFAR calibration and wide-field imaging},
     journal = {Comptes Rendus. Physique},
     pages = {28--32},
     publisher = {Elsevier},
     volume = {13},
     number = {1},
     year = {2012},
     doi = {10.1016/j.crhy.2011.10.006},
     language = {en},
}
TY  - JOUR
AU  - Cyril Tasse
AU  - Ger van Diepen
AU  - Sebastiaan van der Tol
AU  - Reinout J. van Weeren
AU  - Joris E. van Zwieten
AU  - Fabien Batejat
AU  - Sanjay Bhatnagar
AU  - Ilse van Bemmel
AU  - Laura Bîrzan
AU  - Annalisa Bonafede
AU  - John Conway
AU  - Chiara Ferrari
AU  - Francesco De Gasperin
AU  - Kumar Golap
AU  - George Heald
AU  - Neal Jackson
AU  - Giulia Macario
AU  - John McKean
AU  - Niruj Mohan
AU  - Emanuela Orrù
AU  - Roberto Pizzo
AU  - David Rafferty
AU  - Urvashi Rau
AU  - Huub Röttgering
AU  - Aleksandar Shulevski
AU  - on behalf of the LOFAR Collaboration
TI  - LOFAR calibration and wide-field imaging
JO  - Comptes Rendus. Physique
PY  - 2012
SP  - 28
EP  - 32
VL  - 13
IS  - 1
PB  - Elsevier
DO  - 10.1016/j.crhy.2011.10.006
LA  - en
ID  - CRPHYS_2012__13_1_28_0
ER  - 
%0 Journal Article
%A Cyril Tasse
%A Ger van Diepen
%A Sebastiaan van der Tol
%A Reinout J. van Weeren
%A Joris E. van Zwieten
%A Fabien Batejat
%A Sanjay Bhatnagar
%A Ilse van Bemmel
%A Laura Bîrzan
%A Annalisa Bonafede
%A John Conway
%A Chiara Ferrari
%A Francesco De Gasperin
%A Kumar Golap
%A George Heald
%A Neal Jackson
%A Giulia Macario
%A John McKean
%A Niruj Mohan
%A Emanuela Orrù
%A Roberto Pizzo
%A David Rafferty
%A Urvashi Rau
%A Huub Röttgering
%A Aleksandar Shulevski
%A on behalf of the LOFAR Collaboration
%T LOFAR calibration and wide-field imaging
%J Comptes Rendus. Physique
%D 2012
%P 28-32
%V 13
%N 1
%I Elsevier
%R 10.1016/j.crhy.2011.10.006
%G en
%F CRPHYS_2012__13_1_28_0
Cyril Tasse; Ger van Diepen; Sebastiaan van der Tol; Reinout J. van Weeren; Joris E. van Zwieten; Fabien Batejat; Sanjay Bhatnagar; Ilse van Bemmel; Laura Bîrzan; Annalisa Bonafede; John Conway; Chiara Ferrari; Francesco De Gasperin; Kumar Golap; George Heald; Neal Jackson; Giulia Macario; John McKean; Niruj Mohan; Emanuela Orrù; Roberto Pizzo; David Rafferty; Urvashi Rau; Huub Röttgering; Aleksandar Shulevski; on behalf of the LOFAR Collaboration. LOFAR calibration and wide-field imaging. Comptes Rendus. Physique, Volume 13 (2012) no. 1, pp. 28-32. doi : 10.1016/j.crhy.2011.10.006. https://comptes-rendus.academie-sciences.fr/physique/articles/10.1016/j.crhy.2011.10.006/

[1] J.-M. Grießmeier; P. Zarka; M. Tagger Radioastronomy with LOFAR, C. R. Physique, Volume 13 (2012) no. 1, pp. 23-27 ( in this issue )

[2] J. Girard; P. Zarka; M. Tagger; L. Denis; D. Charrier; A.A. Konovalenko; F. Boone Antenna design and distribution for the LOFAR super station, C. R. Physique, Volume 13 (2012) no. 1, pp. 33-37 ( in this issue )

[3] M. de Vos; A.W. Gunst; R. Nijboer The LOFAR Telescope: System architecture and signal processing, IEEE Proceedings, Volume 97 ( August 2009 ), pp. 1431-1437

[4] J.P. Hamaker; J.D. Bregman; R.J. Sault Understanding radio polarimetry. I. Mathematical foundations, Astronomy and Astrophysics Supplement Series, Volume 117 ( May 1996 ), pp. 137-147

[5] J.E. Noordam; O.M. Smirnov The MeqTrees software system and its use for third-generation calibration of radio interferometers, Astronomy & Astrophysics, Volume 524 ( December 2010 ), p. A61+

[6] H.T. Intema; S. van der Tol; W.D. Cotton; A.S. Cohen; I.M. van Bemmel; H.J.A. Röttgering Ionospheric calibration of low frequency radio interferometric observations using the peeling scheme. I. Method description and first results, Astronomy & Astrophysics, Volume 501 ( July 2009 ), pp. 1185-1205

[7] S. van der Tol, Bayesian estimation for ionospheric calibration in radio astronomy, PhD thesis, TU Delft, July 2009.

[8] S. Bhatnagar Calibration and imaging challenges at low radio frequencies: A review of the state of the art (D.J. Saikia; D.A. Green; Y. Gupta; T. Venturi, eds.), The Low-Frequency Radio Universe, Astronomical Society of the Pacific Conference Series, vol. 407, September 2009 (pp. 375+)

[9] T.J. Cornwell; R.A. Perley Radio-interferometric imaging of very large fields – The problem of non-coplanar arrays, Astronomy & Astrophysics, Volume 261 ( July 1992 ), pp. 353-364

[10] T.J. Cornwell; K. Golap; S. Bhatnagar The noncoplanar baselines effect in radio interferometry: The W-projection algorithm, IEEE Journal of Selected Topics in Signal Processing, Volume 2 ( November 2008 ), pp. 647-657

[11] S. Bhatnagar; T.J. Cornwell; K. Golap; J.M. Uson Correcting direction-dependent gains in the deconvolution of radio interferometric images, Astronomy & Astrophysics, Volume 487 ( August 2008 ), pp. 419-429

[12] G. Heald, J. McKean, R. Pizzo, G. van Diepen, J.E. van Zwieten, R.J. van Weeren, D. Rafferty, S. van der Tol, L. Birzan, A. Shulevski, J.D. Swinbank, E.O. Orru, F. de Gasperin, L. Ker, A. Bonafede, G. Macario, C. Ferrari, Recent LOFAR imaging pipeline results, in: ISKAF2010 Science Meeting, 2010.

Cited by Sources:

Comments - Policy