We investigate the effect of atmospheric phase and scintillation anisoplanatism on the measurement of the local
gradient of the wavefront using a Hartmann-Shack type wavefront sensor. This is accomplished by simulation
of the imaging process, starting with 100 synthetic, anisoplanatic phase and scintillation screens that were
computed for several viewing angles and that correspond to Fried parameters of 7 and 12 cm. The screens
are calculated using the approximated turbulence profile at the site selected for the ATST, Haleakala on Maui,
Hawaii, USA. Phase aberrations are propagated through the wavefront sensor, considering each viewing angle in
each subaperture (of adjustable size) separately. The point spread functions (PSF) are calculated for the viewing
directions as well as specified (and adjustable) pixel scale in the sensor camera. Subsequently, these PSFs are
convolved with a typical wavefront sensor lock structure of solar AO systems, an image of solar granulation.
The cross-correlation peak of the thus created anisoplanatic subimages is finally used to find the local gradients
of the wavefront. We find that phase anisoplanatism contributes significantly to the measurement error of a
Hartmann-Shack type wavefront sensor, whereas we cannot detect a notable increase thereof from scintillation
anisoplanatism in the subaperture when using a cross-correlating algorithm to find the gradient of the incident wavefront.