Publications of the Astronomical Society of Australia Publications of the Astronomical Society of Australia Society
Publications of the Astronomical Society of Australia
Publications of the Astronomical Society of Australia

Publications of the Astronomical Society of Australia

Volume 29 Number 3 2012

Source Finding and Visualisation

ASv29n3_PRSource Finding and Visualisation

Bärbel S. Koribalski
pp. 213-213

Large radio surveys, such as those proposed for the Australian SKA Pathfinder (ASKAP), require excellent source-finding algorithms. Here, we discuss advanced methods for finding sources in spectral line, radio continuum and polarisation surveys. We also look into data visualisation to explore the survey results together with their multi-wavelength counterparts.

AS11027 Detection Thresholds and Bias Correction in Polarized Intensity

Samuel J. George, Jeroen M. Stil and Ben W. Keller
pp. 214-220

Detection thresholds in polarized intensity and polarization bias correction are investigated for surveys where the polarization information is obtained from RM synthesis. The false detection rate of sources in polarized intensity is investigated for images with non-Gaussian noise in Stokes Q and U.

AS11026 The Completeness and Reliability of Threshold and False-discovery Rate Source Extraction Algorithms for Compact Continuum Sources

M. T. Huynh, A. Hopkins, R. Norris, P. Hancock, T. Murphy, R. Jurek and M. Whiting
pp. 229-243

The EMU survey with ASKAP aims to utilise an automated source identification and measurement approach that is demonstrably optimal. A key stage in source extraction methods is the background estimation and the choice of a threshold high enough to reject false sources, yet not so high that the catalogues are significantly incomplete. In this analysis, we present results from testing the SExtractor, Selavy (Duchamp), and sfind source extraction tools on simulated radio continuum data.

AS11062 Maser Source-Finding Methods in HOPS

A. J. Walsh, C. Purcell, S. Longmore, C. H. Jordan and V. Lowe
pp. 262-268

We have compared duchamp and manual identification methods for identifying masers in the Galactic plane survey HOPS. We find noise in the data is the limiting factor determining efficiency of both methods. duchamp may be useful for very large datasets, but the manual method is quicker for smaller datasets.

AS11041 Basic Testing of the DUCHAMP Source Finder

T. Westmeier, A. Popping and P. Serra
pp. 276-295

This paper discusses the results of basic source finding tests with the duchamp source finder on different source models. We find duchamp to be a powerful source finder, capable of reliably detecting sources down to low signal-to-noise ratios. duchamp's measurements of basic source parameters, however, are affected by systematic errors.

Existing telescopes rely on human expertise to reduce raw data and then analyse the images for non-pointlike objects; however, the next generation of radio telescopes will make this infeasible. We explore the Circle Hough Transform as a detection method on a sample of different extended circular or arc-like astronomical objects.

AS11067 Comparison of Potential ASKAP HI Survey Source Finders

A. Popping, R. Jurek, T. Westmeier, P. Serra, L. Flöer, M. Meyer and B. Koribalski
pp. 318-339

The large size of the ASKAP Hi surveys DINGO and WALLABY necessitates automated 3D source finding. Here we present a comparison of the performance of five different methods of automated source finding. These source finders are duchamp, gamma-finder, a cnhi finder, a 2d–1d wavelet reconstruction finder and a sigma clipping method (s+c finder).

In this paper we compare four different methods of pre-processing ASKAP Hi spectral line observations to improve source finder performance. We test two conventional methods, linear smoothing and wavelet reconstruction (as implemented by Duchamp). The other two methods we test are iterative median smoothing and mathematical morphology opening subtraction. Both of these methods are not typically used.

We present algorithms used to enhance the source-finding capabilities of duchamp for use in the processing pipelines for the Australian Square Kilometre Array Pathfinder (ASKAP). These algorithms cover parallel processing, variable detection thresholds and two-dimensional fitting. We also discuss the development process and community involvement therein.