  The image quality from Ground-Layer Adaptive Optics (GLAO) can be gradually
increased with decreased contiguous field of view. This trade-off is dependent
on the vertical profile of the optical turbulence (Cn2 profiles). It is known
that the accuracy of the vertical distribution measured by existing Cn2
profiling techniques is currently quite uncertain for wide field performance
predictions 4 to 20 arcminutes. With assumed uncertainties in measurements from
Generalized-SCIDAR (GS), SODAR plus MASS we quantify the impact of this
uncertainty on the trade-off between field of view and image quality for
photometry of science targets at the resolution limit. We use a point spread
function (PSF) model defined analytically in the spatial frequency domain to
compute the relevant photometry figure of merit at infrared wavelengths.
Statistics of this PSF analysis on a database of Cn2 measurements are presented
for Mt. Graham, Arizona and Dome C, Antarctica. This research is part of the
activities of ForOT (3D Forecasting of Optical Turbulence above astronomical
sites).
