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arXiv · 2002.00127

Probabilistic direction-dependent ionospheric calibration for LOFAR-HBA

J. G. Albert·R. J. van Weeren·H. T. Intema·H. J. A. Röttgering
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Abstract

Direction dependent calibration and imaging is a vital part of producing deep, high fidelity, high-dynamic range radio images with a wide-field low-frequency array like LOFAR. Currently, state-of-the-art facet-based direction dependent calibration algorithms rely on the assumption that the isoplanatic-patch size is much larger than the separation between bright in-field calibrators. This assumption is often violated due to the dynamic nature of the ionosphere, and as a result direction dependent errors affect image quality between calibrators. In this paper we propose a probabilistic physics-informed model for inferring ionospheric phase screens, providing a calibration for all sources in the field of view. We apply our method to a randomly selected observation from the LOFAR Two-Metre Sky Survey archive, and show that almost all direction dependent effects between bright calibrators are corrected and that the root-mean-squared residuals around bright sources is reduced by 32\% on average.

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J. G. Albert, R. J. van Weeren, H. T. Intema, H. J. A. Röttgering. 2020-02-01. Probabilistic direction-dependent ionospheric calibration for LOFAR-HBA. https://doi.org/10.1051/0004-6361/201937424

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