A Fast and Exact wstacking and wprojection Hybrid Algorithm for Widefield Interferometric Imaging
Abstract
The standard widefield imaging technique, the wprojection, allows correction for wide fields of view for noncoplanar radio interferometric arrays. However, calculating exact corrections for each measurement has not been possible due to the amount of computation required at high resolution and with the large number of visibilities from current interferometers. The required accuracy and computational cost of these corrections is one of the largest unsolved challenges facing nextgeneration radio interferometers such as the Square Kilometre Array. We show that the same calculation can be performed with a radially symmetric wprojection kernel, where we use onedimensional adaptive quadrature to calculate the resulting Hankel transform, decreasing the computation required for kernel generation by several orders of magnitude, while preserving the accuracy. We confirm that the radial wprojection kernel is accurate to approximately 1% by imaging the zerospacing with an added wterm. We demonstrate the potential of our radially symmetric wprojection kernel via sparse image reconstruction, using the software package PURIFY. We develop a distributed wstacking and wprojection hybrid algorithm. We apply this algorithm to individually correct for noncoplanar effects in 17.5 million visibilities over a 25 by 25 degree FoV Murchison Widefield Array observation for image reconstruction. Such a level of accuracy and scalability is not possible with standard wprojection kernel generation methods. This demonstrates that we can scale to a large number of measurements with large image sizes while still maintaining both speed and accuracy.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 2019
 DOI:
 10.3847/15384357/ab0a05
 arXiv:
 arXiv:1807.09239
 Bibcode:
 2019ApJ...874..174P
 Keywords:

 techniques: image processing;
 techniques: interferometric;
 methods: data analysis;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 9 Figures, 19 Pages. Accepted to ApJ