Principle of correlating Shack-Hartmann wavefront sensor working on granulation. Granulation images formed by a lenslet-array. The central subaperture is fully obstructed by the pick-off mirror for the DST guiding telescope beam. Cross-correlations derived from images referenced a particular subaperture. Shift vectors derived from Cross-Correlations.
Global tilt is removed from the tilt vector map.
Wavefront derived from tilt map using a modal reconstruction scheme.