Results of the GREAT08 Challenge: an image analysis competition for cosmological lensing

Sarah Bridle, Sreekumar T. Balan, Matthias Bethge, Marc Gentile, Stefan Harmeling, Catherine Heymans, Michael Hirsch, Reshad Hosseini, Mike Jarvis, Donnacha Kirk, Thomas Kitching, Konrad Kuijken, Antony Lewis, Stephane Paulin-Henriksson, Bernhard Schoelkopf, Malin Velander, Lisa Voigt, Dugan Witherick, Adam Amara, Gary BernsteinFrederic Courbin, Mandeep Gill, Alan Heavens, Rachel Mandelbaum, Richard Massey, Baback Moghaddam, Anais Rassat, Alexandre Refregier, Jason Rhodes, Tim Schrabback, John Shawe-Taylor, Marina Shmakova, Ludovic van Waerbeke, David Wittman

Research output: Contribution to journalArticlepeer-review


We present the results of the Gravitational LEnsing Accuracy Testing 2008 (GREAT08) Challenge, a blind analysis challenge to infer weak gravitational lensing shear distortions from images. The primary goal was to stimulate new ideas by presenting the problem to researchers outside the shear measurement community. Six GREAT08 Team methods were presented at the launch of the Challenge and five additional groups submitted results during the 6-month competition. Participants analyzed 30 million simulated galaxies with a range in signal-to-noise ratio, point spread function ellipticity, galaxy size and galaxy type. The large quantity of simulations allowed shear measurement methods to be assessed at a level of accuracy suitable for currently planned future cosmic shear observations for the first time. Different methods perform well in different parts of simulation parameter space and come close to the target level of accuracy in several of these. A number of fresh ideas have emerged as a result of the Challenge including a re-examination of the process of combining information from different galaxies, which reduces the dependence on realistic galaxy modelling. The image simulations will become increasingly sophisticated in future GREAT Challenges, meanwhile the GREAT08 simulations remain as a benchmark for additional developments in shear measurement algorithms.

Original languageEnglish
Pages (from-to)2044-2061
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - 1 Jul 2010


  • gravitational lensing: weak
  • methods: data analysis
  • methods: statistical
  • techniques: image processing
  • cosmology: observations
  • large-scale structure of Universe


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