Antarctic site testing - Microthermal measurements of surface-layer seeing at the South Pole

Results from experiments measuring the optical seeing in the surface layer at the South Pole Station are presented. Seeing measurements were taken over 49 data runs between April and August 1994, using microthermal sensors placed at 3 levels on a 27 m-high mast. The seeing contribution from this region was quite large in comparison with similar experiments performed at other sites, with a mean value measured over this period of 0.64 ''. However, there is often a significant decrease in the optical turbulence over the height of the mast, with mean values of 0.37 '' and 0.46 '' measured in the upper (17-27 m) and lower (7-17 m) sections respectively. These measurements coincide with a large and highly variable temperature inversion, the behaviour of which is often well correlated with the observed turbulence profile. The results can be roughly separated into four or five categories, characterised by the temperature inversion alone. Further analysis of the data should provide some predictive power about the likely optical turbulence profile of the surface layer in given observing conditions.