TY - JOUR
T1 - An efficient feedback calibration algorithm for direct imaging radio telescopes
AU - Beardsley, Adam P.
AU - Thyagarajan, Nithyanandan
AU - Bowman, Judd
AU - Morales, Miguel F.
N1 - Funding Information:
National Science Foundation under grant AST-1139974 of the University Radio Observatory program.
Funding Information:
This work has been supported by the National Science Foundation through award AST-1206552. We thank Danny Jacobs for his valuable inputs, and Greg Taylor for providing us with LWA data. Construction of the LWA has been supported by the Office of Naval Research under Contract N00014-07-C-0147. Support for operations and continuing development of the LWA1 is provided by the
Funding Information:
This work has been supported by the National Science Foundation through award AST-1206552. We thank Danny Jacobs for his valuable inputs, and Greg Taylor for providing us with LWA data. Construction of the LWA has been supported by the Office of Naval Research under Contract N00014-07-C-0147. Support for operations and continuing development of the LWA1 is provided by the National Science Foundation under grant AST-1139974 of the University Radio Observatory program.
Publisher Copyright:
© 2017 The Authors.
PY - 2017/10
Y1 - 2017/10
N2 - We present the E-field Parallel Imaging Calibration (EPICal) algorithm, which addresses the need for a fast calibration method for direct imaging radio astronomy correlators. Direct imaging involves a spatial fast Fourier transform of antenna signals, alleviating an O(Na2) computational bottleneck typical in radio correlators, and yielding amore gentleO(Ng log2 Ng) scaling, where Na is the number of antennas in the array and Ng is the number of gridpoints in the imaging analysis. This can save orders of magnitude in computation cost for next generation arrays consisting of hundreds or thousands of antennas. However, because antenna signals are mixed in the imaging correlator without creating visibilities, gain correction must be applied prior to imaging, rather than on visibilities post-correlation.We develop the EPICal algorithm to form gain solutions quickly and without ever forming visibilities. This method scales as the number of antennas, and produces results comparable to those from visibilities. We use simulations to demonstrate the EPICal technique and study the noise properties of our gain solutions, showing they are similar to visibility-based solutions in realistic situations. By applying EPICal to 2 s of Long Wavelength Array data, we achieve a 65 per cent dynamic range improvement compared to uncalibrated images, showing this algorithm is a promising solution for next generation instruments.
AB - We present the E-field Parallel Imaging Calibration (EPICal) algorithm, which addresses the need for a fast calibration method for direct imaging radio astronomy correlators. Direct imaging involves a spatial fast Fourier transform of antenna signals, alleviating an O(Na2) computational bottleneck typical in radio correlators, and yielding amore gentleO(Ng log2 Ng) scaling, where Na is the number of antennas in the array and Ng is the number of gridpoints in the imaging analysis. This can save orders of magnitude in computation cost for next generation arrays consisting of hundreds or thousands of antennas. However, because antenna signals are mixed in the imaging correlator without creating visibilities, gain correction must be applied prior to imaging, rather than on visibilities post-correlation.We develop the EPICal algorithm to form gain solutions quickly and without ever forming visibilities. This method scales as the number of antennas, and produces results comparable to those from visibilities. We use simulations to demonstrate the EPICal technique and study the noise properties of our gain solutions, showing they are similar to visibility-based solutions in realistic situations. By applying EPICal to 2 s of Long Wavelength Array data, we achieve a 65 per cent dynamic range improvement compared to uncalibrated images, showing this algorithm is a promising solution for next generation instruments.
KW - Instrumentation: interferometers
KW - Techniques: image processing
KW - Techniques: interferometric
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U2 - 10.1093/MNRAS/STX1512
DO - 10.1093/MNRAS/STX1512
M3 - Article
AN - SCOPUS:85052100746
SN - 0035-8711
VL - 470
SP - 4720
EP - 4731
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 4
ER -