Weak gravitational lensing induces distortions on the images of background galaxies , and thus provides a direct measure of mass fluctuations in the universe .
The distortion signature from large-scale structure has recently been detected by several groups for the first time , opening promising prospects for the near future .
Since the distortions induced by lensing on the images of background galaxies are only of a few percent , a reliable measurement demands very accurate galaxy shape estimation and a careful treatment of systematic effects .
Here , we present a study of a shear measurement method using detailed simulations of artificial images .
The images are produced using realisations of a galaxy ensemble drawn from the HST Groth strip .
We consider realistic observational effects including atmospheric seeing , PSF anisotropy and pixelisation , incorporated in a manner to reproduce actual observations with the William Herschel Telescope .
By applying an artificial shear to the simulated images , we test the shear measurement method proposed by Kaiser , Squires & Broadhurst ( 1995 , KSB ) .
Overall , we find the KSB method to be reliable with the following provisos .
First , although the recovered shear is linearly related to the input shear , we find a coefficient of proportionality of about 0.8 .
In addition , we find a residual anti-correlation between the PSF ellipticity and the corrected ellipticities of faint galaxies .
To guide future weak lensing surveys , we study how seeing size , exposure time and pixelisation affect the sensitivity to shear .
We find that worsened seeing linearly increases the noise in the shear estimate , while the sensitivity depends only weakly on exposure time .
The noise is dramatically increased if the pixel scale is larger than that of the seeing .
In addition , we study the impact of overlapping isophotes of neighboring galaxies , and find that this effect can produce spurious lensing signals on small scales .
We discuss the prospects of using the KSB method for future , more sensitive , surveys .
Numerical simulations of this kind are a required component of present and future analyses of weak lensing surveys .