Characterisation of the Dome C Atmospheric Boundary Layer Turbulence with a Non-Doppler Acoustic Radar

The Antarctic plateau has superb astronomical seeing above a turbulent boundary layer. This layer has a thickness of between tens of metres and a few hundred metres, depending on the site. We are developing a sonic radar, SNODAR, to measure the turbulence in the boundary layer from 10 to 50 m, and, in particular, to measure the height of the boundary layer to an accuracy of 1 m. Commercial sonic radars typically have a lower limit of about 10 m, and have 10 m range bins. The results from SNODAR should allow a confident assessment of the height at which one must mount a telescope in order to realise the superb free atmosphere seeing from the Antarctic plateau, which has been measured at Dome C to be 0.27 arcsecs on average, and better than 0.15 arcsecs for 25% of the time.