Outer scale is a relevant parameter for the experimental performance evaluation of large telescopes. Different techniques have been used for the outer scale estimation. In situ measurements with radiosounding balloons have given very small values of outer scale. This latter has also been estimated directly at the ground level from the wavefront analysis with High Angular Resolution (HAR) techniques using interferometric or Shack-Hartmann or more generally AO systems data. Dedicated instruments have been also developed for the outer scale monitoring such as the Generalized Seeing Monitor (GSM) and the Monitor of Outer Scale Profile (MOSP). The measured values of outer scale from HAR techniques, GSM and MOSP are somewhat coherent and are larger than the in situ results. The main explanation of this difference comes from the definition of the outer scale itself.

This paper aims to give a review in a non-exhaustive way of different techniques and instruments for the measurement of the outer scale. Comparisons of outer scale measurements will be discussed in the light of the different definitions of this parameter, the associated observable quantities and the atmospheric turbulence model as well.

Date Published: 26 July 2016
PDF: 12 pages
Proc. SPIE 9909, Adaptive Optics Systems V, 99091K (26 July 2016); doi: 10.1117/12.2231375

Published in SPIE Proceedings Vol. 9909:
Adaptive Optics Systems V
Enrico Marchetti; Laird M. Close; Jean-Pierre Véran, Editor(s)