Evolution of Large Scale Structure { Garching , August 1998 SIMULATING WEAK LENSING BY LARGE -

We use numerical simulations of ray tracing through N-body simulations to investigate weak lensing by large-scale structure. Here we focus on the reconstruction of statistics of the convergence eld from noisy data on galaxy ellipticities. On degree scales and smaller the shear and convergence statistics lie in the nonlinear regime and have a non-gaussian distribution. For this regime ray tracing simulations are necessary to provide reliable error estimates and calibration of the measurements. We show how the skewness can in principle be used to probe the mean density in the universe m, but is sensitive to sampling errors and requires large observed areas. We show how measures of non-Gaussianity that use the full probability distribution provide robust discriminators of models with varying m.