TY - JOUR
T1 - Direct wide-field radio imaging in real-time at high time resolution using antenna electric fields
AU - Kent, James
AU - Beardsley, Adam P.
AU - Bester, Landman
AU - Gull, Steve F.
AU - Nikolic, Bojan
AU - Dowell, Jayce
AU - Thyagarajan, Nithyanandan
AU - Taylor, Greg B.
AU - Bowman, Judd
N1 - Funding Information:
Construction of the LWA has been supported by the Office of Naval Research under Contract N00014-07-C-0147 and by the AFOSR. Support for operations and continuing development of the LWA1 is provided by the Air Force Research Laboratory and the National Science Foundation under grants AST-1835400 and AGS-1708855. APB is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1701440. We gratefully acknowledge the support of NVIDIA Corporation with the donation of a Titan X GPUused for prototyping and testing. GBT and JD acknowledge support from NSF/AST award 1711164. JK is funded by Engineering and Physical Sciences Research Council, part of United Kingdom Research and Innovation (UKRI).
Publisher Copyright:
© 2019 The Author(s)
PY - 2020/1/1
Y1 - 2020/1/1
N2 - The recent demonstration of a real-time direct imaging radio interferometry correlator represents a new capability in radio astronomy. However, wide-field imaging with this method is challenging since wide-field effects and array non-coplanarity degrade image quality if not compensated for. Here, we present an alternative direct imaging correlation strategy using a direct Fourier transform (DFT), modelled as a linear operator facilitating a matrix multiplication between the DFT matrix and a vector of the electric fields from each antenna. This offers perfect correction for wide field and non-coplanarity effects. When implemented with data from the Long Wavelength Array (LWA), it offers comparable computational performance to previously demonstrated direct imaging techniques, despite having a theoretically higher floating point cost. It also has additional benefits, such as imaging sparse arrays and control over which sky coordinates are imaged, allowing variable pixel placement across an image. It is in practice a highly flexible and efficient method of direct radio imaging when implemented on suitable arrays. A functioning electric field direct imaging architecture using the DFT is presented, alongside an exploration of techniques for wide-field imaging similar to those in visibility-based imaging, and an explanation of why they do not fit well to imaging directly with the digitized electric field data. The DFT imaging method is demonstrated on real data from the LWA telescope, alongside a detailed performance analysis, as well as an exploration of its applicability to other arrays.
AB - The recent demonstration of a real-time direct imaging radio interferometry correlator represents a new capability in radio astronomy. However, wide-field imaging with this method is challenging since wide-field effects and array non-coplanarity degrade image quality if not compensated for. Here, we present an alternative direct imaging correlation strategy using a direct Fourier transform (DFT), modelled as a linear operator facilitating a matrix multiplication between the DFT matrix and a vector of the electric fields from each antenna. This offers perfect correction for wide field and non-coplanarity effects. When implemented with data from the Long Wavelength Array (LWA), it offers comparable computational performance to previously demonstrated direct imaging techniques, despite having a theoretically higher floating point cost. It also has additional benefits, such as imaging sparse arrays and control over which sky coordinates are imaged, allowing variable pixel placement across an image. It is in practice a highly flexible and efficient method of direct radio imaging when implemented on suitable arrays. A functioning electric field direct imaging architecture using the DFT is presented, alongside an exploration of techniques for wide-field imaging similar to those in visibility-based imaging, and an explanation of why they do not fit well to imaging directly with the digitized electric field data. The DFT imaging method is demonstrated on real data from the LWA telescope, alongside a detailed performance analysis, as well as an exploration of its applicability to other arrays.
KW - Instrumentation: interferometers
KW - Techniques: image processing
KW - Techniques: interferometric
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U2 - 10.1093/mnras/stz3028
DO - 10.1093/mnras/stz3028
M3 - Article
AN - SCOPUS:85079625405
SN - 0035-8711
VL - 491
SP - 254
EP - 263
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 1
ER -