  The present generation of weak lensing surveys will be superseded by surveys
run from space with much better sky coverage and high level of signal to noise
ratio, such as SNAP. However, removal of any systematics or noise will remain a
major cause of concern for any weak lensing survey. One of the best ways of
spotting any undetected source of systematic noise is to compare surveys which
probe the same part of the sky. In this paper we study various measures which
are useful in cross correlating weak lensing surveys with diverse survey
strategies. Using two different statistics - the shear components and the
aperture mass - we construct a class of estimators which encode such
cross-correlations. These techniques will also be useful in studies where the
entire source population from a specific survey can be divided into various
redshift bins to study cross correlations among them. We perform a detailed
study of the angular size dependence and redshift dependence of these
observables and of their sensitivity to the background cosmology. We find that
one-point and two-point statistics provide complementary tools which allow one
to constrain cosmological parameters and to obtain a simple estimate of the
noise of the survey.
