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LEAP: an innovative direction-dependent ionospheric calibration scheme for low-frequency arrays
Rioja, María J.; Dodson, Richard; Franzen, Thomas M. O.
AA(ICRAR, M468, The University of Western Australia, 35 Stirling Hwy, Crawley, Western Australia 6009, Australia; CSIRO Astronomy and Space Science, PO Box 1130, Bentley, WA 6102, Australia; Observatorio Astronómico Nacional (IGN), Alfonso XII, 3 y 5, E-28014 Madrid, Spain 0000-0003-4871-9535), AB(ICRAR, M468, The University of Western Australia, 35 Stirling Hwy, Crawley, Western Australia 6009, Australia 0000-0003-0392-3604), AC(International Centre for Radio Astronomy Research, Curtin University, Bentley, WA 6102, Australia; CSIRO Astronomy and Space Science, PO Box 1130, Bentley, WA 6102, Australia)
Monthly Notices of the Royal Astronomical Society, Volume 478, Issue 2, p.2337-2349 (MNRAS Homepage)
Publication Date:
Astronomy Keywords:
methods: observational, techniques: interferometric, astrometry, radio continuum: general
Abstract Copyright:
2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
Bibliographic Code:


The ambitious scientific goals of the SKA require a matching capability for calibration of atmospheric propagation errors, which contaminate the observed signals. We demonstrate a scheme for correcting the direction-dependent ionospheric and instrumental phase effects at the low frequencies and with the wide fields of view planned for SKA-Low. It leverages bandwidth smearing, to filter out signals from off-axis directions, allowing the measurement of the direction-dependent antenna-based gains in the visibility domain; by doing this towards multiple directions it is possible to calibrate across wide fields of view. This strategy removes the need for a global sky model, therefore all directions are independent. We use MWA results at 88 and 154 MHz under various weather conditions to characterize the performance and applicability of the technique. We conclude that this method is suitable to measure and correct for temporal fluctuations and direction-dependent spatial ionospheric phase distortions on a wide range of scales: both larger and smaller than the array size. The latter are the most intractable and pose a major challenge for future instruments. Moreover, this scheme is an embarrassingly parallel process, as multiple directions can be processed independently and simultaneously. This is an important consideration for the SKA, where the current planned architecture is one of compute-islands with limited interconnects. Current implementation of the algorithm and ongoing developments are discussed.
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