The likely characteristics of the high antarctic plateau for astronomy have been widely discussed, and are described in greater detail elsewhere (e.g. Burton 1996). This experiment forms part of a continuing program of site-testing in Antarctica, being conducted by groups from the University of New South Wales (Australia), the Université de Nice (France) and the Center for Astrophysical Research in Antarctica (U.S.A.), of which the aim is to determine as completely as possible the observing conditions at the South Pole, before performing measurements at more remote sites on the plateau. Several other experiments are in progress, the results from some of which have been reported (Ashley et al. 1996; Nguyen et al. 1996).
The results presented here form the second part of a campaign to determine the
optical seeing at the South Pole, and its variation with altitude, by direct
measurement of the thermal fluctuations associated with the atmospheric
turbulence.
These can be directly related to refractive index variations, which are the
source
of atmospheric seeing. In the first
part of this experiment (Marks et al. 1996) we observed very strong
optical
turbulence close to the surface (
on average in the lowest 27 m),
compared with similar measurements performed at mid-latitude sites
(Vernin & Tuñon-Muñóz 1994;
ESO-VLT working group
1987),
which put the seeing contribution from this region at 
.Individual measurements were highly variable, and often indicated a significant
decrease in optical turbulence with height above the surface.
It became clear from these results
that determining the vertical extent of turbulence in the boundary layer was
of prime importance in characterising the seeing at the site.
In our second season, balloon-borne microthermal sensors were used to obtain integrated values of the seeing over the entire atmosphere, as well as to observe the altitude profile of the optical turbulence. The results of fifteen balloon flights are discussed here, including the relation of the turbulence profile to simultaneously measured temperature and wind velocity gradients. We use the observed correlation between these quantities to speculate on the likely conditions at other sites higher on the plateau.
The strong concentration of optical turbulence in the boundary layer is a highly favourable situation for the use of image correction techniques, and in the final section we quantify some of the important site parameters in adaptive optics, for comparison with the values obtained under the conditions found at mid-latitude sites.
Copyright The European Southern Observatory (ESO)