  The era of the next generation of giant telescopes requires not only the
advent of new technologies but also the development of novel methods, in order
to exploit fully the extraordinary potential they are built for. Global Multi
Conjugate Adaptive Optics (GMCAO) pursues this approach, with the goal of
achieving good performance over a field of view of a few arcmin and an increase
in sky coverage. In this article, we show the gain offered by this technique to
an astrophysical application, such as the photometric survey strategy applied
to the Chandra Deep Field South as a case study. We simulated a close-to-real
observation of a 500 x 500 arcsec^2 extragalactic deep field with a 40-m class
telescope that implements GMCAO. We analysed mock K-band images of 6000
high-redshift (up to z = 2.75) galaxies therein as if they were real to recover
the initial input parameters. We attained 94.5 per cent completeness for source
detection with SEXTRACTOR. We also measured the morphological parameters of all
the sources with the two-dimensional fitting tools GALFIT. The agreement we
found between recovered and intrinsic parameters demonstrates GMCAO as a
reliable approach to assist extremely large telescope (ELT) observations of
extragalactic interest.
