Ionospheric calibration of low frequency radio interferometric observations using the peeling scheme I. Method description and first results

By H. Intema, S. Tol, W. Cotton, A. Cohen, I. V. Bemmel, H. Röttgering. 2009

229 citations recorded by the source corpus.

Calibration of radio interferometric observations becomes increasingly difficult towards lower frequencies. Below ∼300 MHz, spatially variant refractions and propagation delays of radio waves traveling through the ionosphere cause phase rotations that can vary significantly with time, viewing direction and antenna location. In this article we present a description and first results of SPAM (Source Peeling and Atmospheric Modeling), a new calibration method that attempts to iteratively solve and correct for ionospheric phase errors. To model the ionosphere, we construct a time-variant, 2-dimensional phase screen at fixed height above the Earth’s surface. Spatial variations are described by a truncated set of discrete Karhunen-Loeve base functions, optimized for an assumed power-law spectral density of free electrons density fluctuations, and a given configuration of calibrator sources and antenna locations. The model is constrained using antenna-based gain phases from individual self-calibrations on the available bright sources in the field-of-view. Application of SPAM on three test cases, a simulated visibility data set and two selected 74 MHz VLA data sets, yields significant improvements in image background noise (5–75 percent reduction) and source peak fluxes (up to 25 percent increase) as compared to the existing self-calibration and field-based calibration methods, which indicates a significant improvement in ionospheric phase calibration accuracy.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/0e3d5013b69506313d291206f33b8e7d7beef7f8

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Citations in the corpus

The GMRT 150 MHz all-sky radio survey - First alternative data release TGSS ADR1 (2016, methodology): “One of the main DDEs is ionospheric dispersive delay, which causes smearing of sources (ionospheric “seeing”) as well as relatively large residual sidelobe structure across the pointing image when processed using only direction-independent self-calibration (e.g., Intema et al. 2009).”
Reionization and the Cosmic Dawn with the Square Kilometre Array (2012, background): “A number of different approaches (or suggested approaches) have been taken thus far (e.g. Intema et al. 2009; Matejek & Morales 2009), among which are multiple phase screens, “rubber-sheet“ models (which correct mostly for source motion, i.e. equivalent to tip-tilt corrections in the optical),…”
Diffuse Radio Emission from Galaxy Clusters (2019, methodology): “We acknowledge the help of Soumyajit Mandal, Huib Intema, and Dawoon Jung for making some of the displayed GMRT images with SPAM (Intema et al. 2009; Intema 2014).”
LOFAR 150-MHz observations of the Boötes field: catalogue and source counts (2016, methodology): “…for. van Weeren et al. (2016, herafter vW16) have recently presented a new scheme for calibrating the DDEs and imaging LOFAR data that combines elements from existing direction-dependent calibration methods such as SPAM (Intema et al. 2009) and SAGECAL (Yatawatta et al. 2013; Kazemi et al. 2011).”
LOFAR FACET CALIBRATION (2016, methodology): “However, field-based calibration methods are not suitable for arrays with very long baselines such as LOFAR (Lonsdale 2005; Intema et al. 2009).”