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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
earth and planetary sciences
Applying full polarization A-Projection to very wide field of view instruments: An imager for LOFAR
Astronomy and Astrophysics, Volume 553, Article A105, Year 2013
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Description
The required high sensitivities and large fields of view of the new generation of radio interferometers impose high dynamic ranges, e.g., ~1:10 6 to 1:108 for the Square Kilometre Array (SKA). The main problem for achieving these high ranges is the calibration and correction of direction dependent effects (DDE) that can affect the electro-magnetic field (antenna beams, ionosphere, Faraday rotation, etc.). It has already been shown that the A-Projection is a fast and accurate algorithm that can potentially correct for any given DDE in the imaging step. With its very wide field of view, low operating frequency (~30-250 MHz), long baselines, and complex station-dependent beam patterns, the LOw Frequency ARray (LOFAR) is certainly the most complex SKA pathfinder instrument. In this paper we present a few implementations of the A-Projection in LOFAR which can deal nondiagonal Mueller matrices. The algorithm is designed to correct for all DDE, including individual antennas, projection of the dipoles on the sky, beam forming, and ionospheric effects. We describe a few important algorithmic optimizations related to LOFAR's architecture that allowed us to build a fast imager. Based on simulated datasets we show that A-Projection can dramatically improve the dynamic range for both phased array beams and ionospheric effects. However, certain problems associated with the calibration of DDE remain (especially ionospheric effects), and the effect of the algorithm on real LOFAR survey data still needs to be demonstrated. We will be able to use this algorithm to construct the deepest extragalactic surveys, comprising hundreds of days of integration. © ESO, 2013.
Authors & Co-Authors
Tasse, Cyril
France, Paris
Gepi - Galaxies, Etoiles, Physique, Instrumentation
South Africa, Grahamstown
Rhodes University
South Africa, Pinelands
Square Kilometre Array, South Africa
van der Tol, Sebastiaan
Netherlands, Leiden
Sterrewacht Leiden
van Zwieten, Joris E.
Netherlands, Dwingeloo
Netherlands Foundation for Research in Astronomy
van DIepen, Ger N.J.
Netherlands, Dwingeloo
Netherlands Foundation for Research in Astronomy
Bhatnagar, Sanjay
United States, Socorro
National Radio Astronomy Observatory Socorro
Statistics
Citations: 111
Authors: 5
Affiliations: 6
Identifiers
Doi:
10.1051/0004-6361/201220882
ISSN:
00046361
e-ISSN:
14320746
Study Design
Cross Sectional Study
Study Approach
Quantitative