  The Calibration enhancement effort for the Space Telescope Imaging
Spectrograph (STIS) aims to improve data calibration via the application of
physical modelling techniques.
  We describe here a model of the Charge Transfer process during read-out of
modern Charge Coupled Devices, and its application to data from STIS. The model
draws upon previous investigations of this process and, in particular, the
trapping and emission model developed by Robert Philbrick of Ball Aerospace.
  Early comparison to calibration data is encouraging. Essentially, a physical
description of the STIS CCD combined with the physics of known defects in the
silicon lattice expected to arise in a hostile radiation environment, is enough
to yield results which approximately match real data. Uncertainties remain,
however, in the details of the model and the physical description of STIS.
