Stefan J. Wijnholds, "Imaging with the SKA core", SKA2010 -
International SKA Science and Engineering Meeting, Manchester (UK), 22-25
extended abstract: The moderate resolution and high brightness
sensitivity of the SKA core may be exploited to study the diffuse structures
in our Galaxy, the IGM and the cosmic web. The combination of high sensitivity
and moderate resolution leads to confusion limited maps at each frequency from
which the source components along each line-of-sight may be extracted by
exploiting the difference in spectral characteristics of the individual
sources. This extraction can only be successful if the individual maps are
made using a reliable and consistent method.
Least squares imaging has several attractive features that make it well
suited for imaging with the SKA core:
- The model based imaging (deconvolution) problem can be solved in closed
- The closed form solution for the complete grid of pixels in the image is
mathematically identical to the solution for simultaneous source power
estimation in the self-calibration process (see ), which should facilitate
integration of the calibration and imaging processes.
- The availability of a closed form solution allows for a complete error and
noise propagation analysis .
- It implicitly handles arbitrary direction dependent effects that may vary
over time and frequency during the observation .
- The numerical complexity of the deconvolution operation only depends on
the number of image parameters regardless of the amount of visibility data
- It has been demonstrated that the algorithm reaches the Cramer-Rao bound
on actual data . The Cramer-Rao bound is the lower bound on the total
variance on the estimated parameters for an unbiased estimator.
In this presentation I discuss the strengths and weaknesses of l_2-based
image optimization to demonstrate its suitability for imaging with the SKA
core. I illustrate this by application to actual LOFAR data. I also discuss
the numerical complexity of the algorithm demonstrating that this is a viable
option for imaging with the SKA core.
- Stefan J. Wijnholds, Fish-Eye Imaging With A LOFAR Station. In Proceedings
of the International Union of Radio Science (URSI) Benelux Forum, Delft, The
Netherlands, 8 June 2009.
- Stefan J. Wijnholds, Least Squares All-Sky Imaging With A LOFAR
Station. In SKA Calibration and Imaging Workshop (CalIm), Socorro (New
Mexico), USA, 30 March - 3 April 2009.
- Stefan J. Wijnholds and Alle-Jan van der Veen, Fundamental Imaging Limits
of Radio Telescope Arrays. IEEE Journal of Selected Topics in Signal
Processing, 2(5):613-623, October 2008.
- Stefan J. Wijnholds and Alle-Jan van der Veen, Multisource
Self-calibration for Sensor Arrays. IEEE Transactions on Signal Processing,
57(9):3512-3522, September 2009.
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