  Using five independent analytic and Monte Carlo simulation codes, we have
studied the performance of wide field ground layer adaptive optics (GLAO),
which can use a single, relatively low order deformable mirror to correct the
wavefront errors from the lowest altitude turbulence. GLAO concentrates more
light from a point source in a smaller area on the science detector, but unlike
traditional adaptive optics, images do not become diffraction-limited. Rather
the GLAO point spread function (PSF) has the same functional form as a
seeing-limited PSF, and can be characterized by familiar performance metrics
such as Full-Width Half-Max (FWHM). The FWHM of a GLAO PSF is reduced by 0.1"
or more for optical and near-infrared wavelengths over different atmospheric
conditions. For the Cerro Pachon atmospheric model this correction is even
greater when the image quality is worst, which effectively eliminates
"bad-seeing" nights; the best seeing-limited image quality, available only 20%
of the time, can be achieved 60 to 80% of the time with GLAO. This
concentration of energy in the PSF will reduce required exposure times and
improve the efficiency of an observatory up to 30 to 40%. These performance
gains are relatively insensitive to a number of trades including the exact
field of view of a wide field GLAO system, the conjugate altitude and actuator
density of the deformable mirror, and the number and configuration of the guide
stars.
