Abstract
The first measurements of the spatial coherence outer scale L [0] at the Observatorio Astronómico Nacional at San Pedro Mártir, Mexico, are reported. This parameter was measured with the Generalized Seeing Monitor of Nice University, France. A log-normal distribution is found with a median value of 27.0 m. The importance of L [0] in the derivation of adaptive optics (AO) performances is discussed. It is shown that low L [0] values boost the corrective ability of low-order AO, but have almost no effect on high-order AO performances.
