2010MNRAS.404..144M

A characterization of the optical turbulence vertical distribution (C²_Nprofiles) and all the main integrated astroclimatic parameters derived from the C²_N and the wind speed profiles above the site of the Large Binocular Telescope (LBT) (Mt Graham, Arizona, USA) is presented. The statistics include measurements related to 43 nights done with a Generalized SCIDAR (GS) used in standard configuration with a vertical resolution ΔH ∼ 1 km on the whole 20 km and with the new technique (High Vertical Resolution GS) in the first kilometre. The latter achieves a resolution ΔH ∼ 20-30 m in this region of the atmosphere. Measurements done in different periods of the year permit us to provide a seasonal variation analysis of the C²_N. A discretized distribution of C²_N, useful for the Ground Layer Adaptive Optics (GLAO) simulations, is provided and a specific analysis for the LBT Laser Guide Star system ARGOS (running in GLAO configuration) case is done including the calculation of the `grey zones' for J, H and K bands. Mt Graham is confirmed to be an excellent site with median values of the seeing without dome contribution ε = 0.72 arcsec, the isoplanatic angle θ₀= 2.5 arcsec and the wavefront coherence time τ₀= 4.8 ms. We find that the OT vertical distribution decreases in a much sharper way than what has been believed so far in the proximity of the ground above astronomical sites. We find that 50 per cent of the whole turbulence develops in the first 80±15 m from the ground. We finally prove that the error in the normalization of the scintillation that has been recently demonstrated in the principle of the GS technique affects these measurements by an absolutely negligible quantity (0.04 arcsec).