Atmospheric outer scale profiling for wide-field adaptive optics

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All major ground-based observatories are equipped with adaptive optics systems to compensate for image distortion caused by atmospheric turbulence. Overcoming the effects of turbulence allows ground-based telescopes to routinely beat the spatial resolving power of their space-based counterparts. For the next generation of 30-40m diameter 'extremely large' telescopes the interaction between the telescope structure, the surface layers of the atmosphere and the adaptive optics system becomes complex. Existing models of atmospheric turbulence describe a characteristic outer scale that constrains the magnitude of refractive index fluctuations across the largest spatial scales. For extremely large telescopes, the impact of a time-varying outer scale on adaptive optics and telescope control can severely degrade image quality and limits the fraction of the observable sky. Characterisation of the outer scale is the biggest unsolved problem in profiling as it cannot be easily disentangled from telescope errors. The aim of this project is to characterise the outer scale in the local environment of the telescope where turbulence is typically strongest and assess the impact of this on the performance of the next generation of adaptive optics instruments.