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Coordination Team:THOMAS KITCHING, ADAM AMARA, SARAH BRIDLE, MANDEEP GILL, CATHERINE HEYMANS, RICHARD MASSEY, BARNABY ROWE, LISA VOIGT

Advisory Team:SREE BALAN, GARY BERNSTEIN, MATTHIAS BETHGE, FREDERIC COURBIN, MARC GENTILE, STEFAN HARMELING, ALAN HEAVENS, MICHAEL HIRSCH, RESHAD HOSSEINI, DONNACHA KIRK, KONRAD KUIJKEN, RACHEL MANDELBAUM, BABACK MOGHADDAM, GULDARIYA NURBAEVA, STEPHANE PAULIN-HENRIKSSON, ANAIS RASSAT, JASON RHODES, BERNHARD SCHOLKOPF, TIM SCHRABBACK, JOHN SHAWE-TAYLOR, MARINA SHMAKOVA, ANDY TAYLOR, MALIN VELANDER, LUDOVIC VAN WAERBEKE, DUGAN WITHERICK, DAVID WITTMAN

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The Challenge of Measuring ShapesThe Challenge of Measuring Shapes

Typical starUsed for finding Convolution kernel

Typical galaxyused for cosmicshear analysis

Slide from S. Bridle

5/19

Cosmic LensingCosmic Lensing

Real data:gi~0.03

gi~0.2

Slide from S. Bridle

6/19

Atmosphere and TelescopeAtmosphere and Telescope

Convolution with kernel

Real data: Kernel size ~ Galaxy size

Slide from S. Bridle

7/19

PixelisationPixelisation

Sum light in each square

Real data: Pixel size ~ Kernel size /2

Slide from S. Bridle

8/19

NoiseNoise

Mostly Poisson. Some Gaussian and bad pixels.Uncertainty on total light ~ 5 per cent

Slide from S. Bridle

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Need to measure shear to 10-3

Current MethodsCurrent Methods

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STEP : Shear Testing Programme STEP : Shear Testing Programme

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Heymans et al., 2006; Massey et al., 2007 & Kitching et al., 2008

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KSB

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Quality FactorQuality Factor

Kitching et al., 2008 (form filling functions); Amara & Refregier (2007)

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7 non-lensing participantsQ~1000 in some regimes

GREAT08 : Stacking Procedure is Important

GREAT08 : Stacking Procedure is Important

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Winning Methods (Q=1000) Stacked the Data

Average Data

AverageEstimators

IndividualObject

Statistic

EnsembleStatistic

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2006 2008 2010

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Massey et al. 2008 Fu et al. 2008

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Bonus Star Challenge: Reconstruct the PSF at non-star positions

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Take Part and Help CosmologyTake Part and Help Cosmology

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http://www.greatchallenges.info/http://www.greatchallenges.info/

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GREAT10 Handbook, Kitching et al., 2010

“Every time the amount of data increases by a factor of ten we should totally rethink the way we analyze it”

Jerome Freidman, Data Mining and Statistics, 1997

http://www.greatchallenges.info/http://www.greatchallenges.info/