NAOS on-line characterization of turbulence parameters and adaptive optics performance

An on-line estimation of turbulence parameters (r(0), L-0 and wind speed) and adaptive optics (AO) performance is presented. The method is based on the reconstruction of open-loop data from deformable mirror voltages and residual wavefront sensor slopes obtained in closed loop. This dedicated tool implemented in the real time computer of the NAOS (Nasmyth adaptive optics system) system (first AO of the very large telescope) allows us without any loop opening to automatically monitor and display (every 15 s) both the atmospheric conditions and the system performance. We have validated the algorithm and tested its robustness on simulated and experimental data (both in the laboratory and on sky). Using data obtained over more than one year (from January 2002 to June 2003), a statistical study on NAOS performance and turbulence characteristics is proposed.