Usage of Large Binocular Telescope pupils to estimate the local outer scale of turbulence

The design of adaptive optics systems is driven by the local characteristics of the atmospheric turbulence. Site characterization campaigns utilizing a variety of atmospheric monitoring equipment provides a statistical description of parameters such integrated seeing, vertical distribution of turbulence strength as well as the coherent time of the turbulence. Modeling work, intended to understand the operation bandwidth of adaptive optics systems make use of Kolmogorov turbulence theory as well as time series of atmospheric parameters obtained from regression analysis based on site characterization data. However, most of the time, even in the more detailed studies, one parameter though important is not measured and monitored with the same attention than the other turbulence parameters, namely, the outer scale of the turbulence. The image quality in large aperture telescopes has been shown to have an important dependence on the instantaneous magnitude of the outer scale of the turbulence. In general terms, the shorter the outer scale of the turbulence, the lower the wavefront variance over the aperture of the imaging system and consequently the higher the image quality. This study focuses in using reconstructed open loop wavefront sensor data observed simultaneously by the two apertures of the Large Binocular Telescope (LBT) to compute and monitor the outer scale of the turbulence.