MEASUREMENT OF ATMOSPHERIC ISOPLANATISM USING STELLAR SCINTILLATION

Comparison of the scintillation of a double star and a nearby single star can be used to indicate the difference in the structure of atmospheric turbulence along two paths which have the angular separation of the double star. This method is not restricted by the diffraction limit of imaging systems and so may be used to measure the isoplanatic angle associated with the smallest scales of the scintillation pattern. Such measurements are relevant to schemes to compensate ground-space laser beams so that they propagate undistorted by atmospheric turbulence. We present observations of Alpha and Beta Crucis under conditions of weak to strong scintillation. These show that the associated turbulent structure was generally different along two paths separated by 21 μrad. On one occasion this anisoplanatism is confirmed to have been associated with scintillation patterns about 3 cm in size, produced by turbulence at an altitude of 1 km. © 1990.