The HAR observing methods such as Adaptive Optics and
Interferometery, require a better understanding of the behavior of
the perturbed wavefronts, more exactly a better knowledge of the
atmospheric turbulence model in addition to the associate
parameters. This is very crucial for modeling the HAR techniques and
particularly for the evaluation of their performance. Indeed, it is
well-known that the performance of an AO system depends upon the
seeing conditions, the outer scale, the isoplanatic angle and the
coherence time. A review of the site-testing instruments deployed at
Dome C will be given, their pertinence and their implications on HAR
techniques will be discussed comparatively to the Paranal site.