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 50m, and, in particular, to measure the height of the boundary layer to an accuracy of 1m. Commercial sonic radars typically have a lower limit of about 10m, and have 10m 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 DomeC to be 0.27 arcsecs on average, and better than 0.15 arcsecs for 25% of the time.