  Deep observations of the Universe, usually as a part of sky surveys, are one
of the symbols of the modern astronomy because they can allow big
collaborations, exploiting multiple facilities and shared knowledge. The new
generation of extremely large telescopes will play a key role because of their
angular resolution and their capability in collecting the light of faint
sources. Our simulations combine technical, tomographic and observational
information, and benefit of the Global-Multi Conjugate Adaptive Optics (GMCAO)
approach, a well demonstrated method that exploits only natural guide stars to
correct the scientific field of view from the atmospheric turbulence. By
simulating K-band observations of 6000 high redshift galaxies in the Chandra
Deep Field South area, we have shown how an ELT can carry out photometric
surveys successfully, recovering morphological and structural parameters. We
present here a wide statistics of the expected performance of a GMCAO-equipped
ELT in 22 well-known surveys in terms of SR.
