Where is the surface-layer turbulence?

Remote turbulence sensing in the first 100m above ground using lunar scintillation has revealed that the seeing measured by regular site monitors can be over-estimated. This explains the well-known discrepancy between the VLT image quality and the seeing measured by the DIMM at Paranal. The concept of ”site seeing” needs to be critically reviewed, considering strong dependence of this parameter on the height of site monitors and on the local turbulence in their immediate vicinity. Higher resolution of ground-based telescopes can be reached if we accept that the natural seeing can be better than shown by the DIMMs and that the contribution of telescope and its environment to the seeing can be significant on nights with superb conditions. This is particularly relevant to the wide-angle optical and IR telescopes which do not rely on adaptive optics. Eventually, a wide-angle adaptive optics will remove local and instrumental distortions and will deliver images truly limited by the atmosphere.