Improving the resolution of ground-based telescopes

Atmospheric turbulence profoundly limits the angular resolution of astronomical telescopes working at visible and near-infrared wavelengths. In fact, the angular resolution for conventional imaging through turbulence is on the order of 5–20t% of the diffraction-limited resolution at the best observatories in the world. The origin of these performance degradations is random turbulence-induced fluctuations in the index of refraction of the atmosphere. Random index-of-refraction fluctuations producing the optical path length of the atmosphere to be random in both space and time, producing random aberrations in the telescope pupil that degrade imaging performance. Over the past several years significant advances have been made in developing both hardware and image-processing-based techniques for improving the resolution of astronomical telescopes. Hardware-oriented correction techniques are based on wave-front sensing and adaptive optics. Image-processing-based methods include speckle-imaging techniques and hybrid imaging techniques that use elements of adaptive-optics systems and image reconstruction. Analysis techniques for predicting the performance of these imaging methods have been developed, and the comparative performance of these imaging techniques has been examined. This paper discusses turbulence and image-detection statistics, describes the fundamentals of methods for overcoming turbulence effects, and provides representative performance results.