The Third Gravitational Lensing Accuracy Testing (GREAT3) Challenge Handbook

TL;DR

The GREAT3 challenge is a community effort to improve and evaluate methods for precise galaxy shape measurement in astronomical images, addressing key effects relevant to upcoming weak lensing surveys.

Contribution

It introduces a comprehensive challenge with realistic simulations testing complex galaxy models, spatially varying PSFs, and multi-exposure data, with publicly available software and benchmarks.

Findings

Benchmarking of existing shape measurement methods.

Identification of key challenges in weak lensing analysis.

Community engagement in method development.

Abstract

The GRavitational lEnsing Accuracy Testing 3 (GREAT3) challenge is the third in a series of image analysis challenges, with a goal of testing and facilitating the development of methods for analyzing astronomical images that will be used to measure weak gravitational lensing. This measurement requires extremely precise estimation of very small galaxy shape distortions, in the presence of far larger intrinsic galaxy shapes and distortions due to the blurring kernel caused by the atmosphere, telescope optics, and instrumental effects. The GREAT3 challenge is posed to the astronomy, machine learning, and statistics communities, and includes tests of three specific effects that are of immediate relevance to upcoming weak lensing surveys, two of which have never been tested in a community challenge before. These effects include realistically complex galaxy models based on high-resolution imaging from space; spatially varying, physically-motivated blurring kernel; and combination of multiple different exposures. To facilitate entry by people new to the field, and for use as a diagnostic tool, the simulation software for the challenge is publicly available, though the exact parameters used for the challenge are blinded. Sample scripts to analyze the challenge data using existing methods will also be provided. See http://great3challenge.info and http://great3.projects.phys.ucl.ac.uk/leaderboard/ for more information.