Measurements of profiles of the wavefront outer scale using observations of the limb of the Moon

The wavefront outer scale is an important parameter to use when evaluating the experimental performance of large aperture telescopes. Knowledge of three-dimensional atmospheric wavefront distortions is required for specifications of multiconjugate adaptive optics systems, which are essential for observations using Extremely Large Telescopes with a wider field of view. We aim to estimate the vertical distribution of the wavefront outer scale. We analyse the angular correlation of the fluctuations of the wavefront angle of arrival, deduced from image motion of the limb of the Moon. We use a simulated annealing algorithm to deduce the height dependence of the wavefront outer scale with given C-N(2) profiles simultaneously measured with the scintillation detection and ranging (SCIDAR) instrument. We present results obtained during two campaigns of observation at the Mauna Kea Observatory (Hawaii) and the Observatoire de Haute Provence (France). Estimated profiles of the outer scale exhibit smaller values in the boundary layer than in the free atmosphere. Comparisons with measurements of the outer scale using the Generalized Seeing Monitor (GSM) are possible and give good agreement. We consider some implications for adaptive optics systems.