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  4. LEAP: Looking beyond pixels with continuous-space EstimAtion of Point sources
 
research article

LEAP: Looking beyond pixels with continuous-space EstimAtion of Point sources

Pan, Hanjie  
•
Simeoni, Matthieu Martin Jean-Andre  
•
Hurley, Paul
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2017
Astronomy & Astrophysics

Context. Two main classes of imaging algorithms have emerged in radio interferometry: the CLEAN algorithm and its multiple variants, and compressed-sensing inspired methods. They are both discrete in nature, and estimate source locations and intensities on a regular grid. For the traditional CLEAN-based imaging pipeline, the resolution power of the tool is limited by the width of the synthesized beam, which is inversely proportional to the largest baseline. The finite rate of innovation (FRI) framework is a robust method to find the locations of point-sources in a continuum without grid imposition. The continuous formulation makes the FRI recovery performance only dependent on the number of measurements and the number of sources in the sky. FRI can theoretically find sources below the perceived tool resolution. To date, FRI had never been tested in the extreme conditions inherent to radio astronomy: weak signal / high noise, huge data sets, large numbers of sources. Aims. The aims were (i) to adapt FRI to radio astronomy, (ii) verify it can recover sources in radio astronomy conditions with more accurate positioning than CLEAN, and possibly resolve some sources that would otherwise be missed, (iii) show that sources can be found using less data than would otherwise be required to find them, and (v) show that FRI does not lead to an augmented rate of false positives. Methods. We implemented a continuous domain sparse reconstruction algorithm in Python. The angular resolution performance of the new algorithm was assessed under simulation, and with visibility measurements from the LOFAR telescope. Existing catalogs were used to confirm the existence of sources. Results. We adapted the FRI framework to radio interferometry, and showed that it is possible to determine accurate off-grid point source locations and their corresponding intensities. In addition, FRI-based sparse reconstruction required less integration time and smaller baselines to reach a comparable reconstruction quality compared to a conventional method. The achieved angular resolution is higher than the perceived instrument resolution, and very close sources can be reliably distinguished. The proposed approach has cubic complexity in the total number (typically around a few thousand) of uniform Fourier data of the sky image estimated from the reconstruction. It is also demonstrated that the method is robust to the presence of extended-sources, and that false-positives can be addressed by choosing an adequate model order to match the noise level.

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Type
research article
DOI
10.1051/0004-6361/201731828
Web of Science ID

WOS:000418460000002

Author(s)
Pan, Hanjie  
Simeoni, Matthieu Martin Jean-Andre  
Hurley, Paul
Blu, Thierry  
Vetterli, Martin  
Date Issued

2017

Published in
Astronomy & Astrophysics
Volume

608

Article Number

A136

Subjects

techniques: Interferometric

•

methods: numerical

•

techniques: image processing

•

LCAV-SSP

URL

Code repository

https://github.com/hanjiepan/LEAP
Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
LCAV  
RelationURL/DOI

IsSupplementedBy

https://doi.org/10.5281/zenodo.1044019
Available on Infoscience
October 17, 2017
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/141479
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