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

H. T. Intema; S. van der Tol; W. D. Cotton; A. S. Cohen; I. M. van Bemmel; H. J. A. Röttgering

doi:10.1051/0004-6361/200811094

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Volume 501 / No 3 (July III 2009)

A&A, 501 3 (2009) 1185-1205

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Table 1:

Overview of the processing parameters for the three data sets that are handled with SPAM as defined in the test cases.
Field name	VLSS J0900+398 (simulated)	VLSS J0900+398 (real)	VLSS J1300-208 (real)
Pixel size^a	18.9 $^{\prime \prime }$	18.9 $^{\prime \prime }$	11.1 $^{\prime \prime }$
Number of facets	347	243	576
Facet separation	$1.18^{\circ}$	$1.18^{\circ}$	$0.62^{\circ}$
SPAM calibration cycles^b	1	1	3
Peeling sources	10^c	11	9
KL model height	1000 km^d	200 km	200 km
Fitted KL model terms	15	15	20^e
Rejected time intervals	0 / 464	25 / 464	86 / 484
Model fit phase rms	$3.0^{\circ}\pm 0.8^{\circ}$	$21.3^{\circ}\pm 2.4^{\circ}$	$23.2^{\circ}\pm 3.2^{\circ}$
Peeling corrections applied directly	no	yes	yes

^a The pixel size for all field-based calibration images is 20 $^{\prime \prime }$ . ^b Adding more cycles did not significantly improve the image quality. ^c Arbitrarily limited to mimic a more realistic scenario. ^d Increased to improve match with FBC phase screen. ^e In this case, 15 terms proved to be insufficient.

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