Remote wave-front sensing using atmospheric scintillations

Wavefront sensors for adaptive optics measure the phase error produced by all layers of atmospheric turbulence. In doing so, they also measure the scintillation pattern in the aperture plane of the telescope for calibration purposes. However, scintillation can provide information about wavefronts in the higher atmosphere (7 - 10 km). This is because it is produced as Fresnel diffraction of high elevation turbulence. Scintillation can also be viewed as a laplacian of the same high altitude perturbations, when there is no middle level turbulence. Thus it can be inverted to yield these perturbations. Using this additional information, adaptive optics systems could correct for either low- or high-elevation turbulence (or both), and increase the field of view available for observation. The method is limited to high intensity and small size of the reference star, absence of middle level turbulence, and narrow spectral response by the detector.