  Exploiting the full statistical power of future cosmic shear surveys will
necessitate improvements to the accuracy with which the gravitational lensing
signal is measured. We present a framework for calibrating shear with image
simulations that demonstrates the importance of including realistic
correlations between galaxy morphology, size and more importantly, photometric
redshifts. This realism is essential so that selection and shape measurement
biases can be calibrated accurately for a tomographic cosmic shear analysis. We
emulate Kilo-Degree Survey (KiDS) observations of the COSMOS field using
morphological information from {\it Hubble} Space Telescope imaging, faithfully
reproducing the measured galaxy properties from KiDS observations of the same
field. We calibrate our shear measurements from lensfit, and find through a
range of sensitivity tests that lensfit is robust and unbiased within the
allowed 2 per cent tolerance of our study. Our results show that the
calibration has to be performed by selecting the tomographic samples in the
simulations, consistent with the actual cosmic shear analysis, because the
joint distributions of galaxy properties are found to vary with redshift.
Ignoring this redshift variation could result in misestimating the shear bias
by an amount that exceeds the allowed tolerance. To improve the calibration for
future cosmic shear analyses, it will be essential to also correctly account
for the measurement of photometric redshifts, which requires simulating
multi-band observations.
