Publisher Summary This chapter discusses the effects of atmospheric turbulence in optical astronomy, summarizes the present state of the theory, reviews the experimental checks that have been made, and discusses the implications in the domain of astronomical observations. Diffraction limited resolution has been obtained with large telescopes up to magnitude 13 by means of speckle interferometry. A Michelson interferometer is already working in the visible on a 20 m baseline up to magnitude 4, and many projects are nearing completion. However, such technological progress can be useful only if accurate quantitative measurements prove to be feasible through atmospheric turbulence. In addition, much work remains to be done before achieving a full understanding of atmospheric effects. The relationship between isoplanicity or speckle boiling and the structure of the atmosphere is still not clear.

V The Effects of Atmospheric Turbulence in Optical Astronomy

The most recent developments on the propagation of optical beams in a turbulent medium, such as the clear atmosphere, are reviewed. Among the phenomena considered are beam spreading, beam wander, loss of coherence, scintillations, angle-of-arrival variations, and short-pulse effects.

Electromagnetic beam propagation in turbulent media

Modified astronomical speckle interferometry “speckle masking”

In 1975, we reviewed the recent developments on wave propagation in turbulent media. In this paper, we update that paper to include recent results on adaptive optics, intensity scintillations, pulse propagation, atmospheric measurements at visible, IR, and millimeter wave frequencies, speckle interferometry, and other related topics.

Electromagnetic beam propagation in turbulent media: An update

A method to obtain an estimate of Fried’s seeing parameter r0 from time series of an arbitrarily shaped, resolved structure that exhibits degradation resulting from atmospheric turbulence is presented. The basic idea is to evaluate the ratio of the observed squared modulus of the average Fourier transform and the observed average power spectrum. The theory of the method is developed, and the influence of noise on the ratio is discussed. The method has been applied to five consecutive time series of observations of solar granulation under different seeing conditions. The power spectra, which are reconstructed with appropriate theoretical modulation transfer functions, converge.

Estimating Fried’s parameter from a time series of an arbitrary resolved object imaged through atmospheric turbulence

A new technique (speckle interferometry) has been developed by Gezari, Labeyrie, and Stachnik, which allows the measurement of stellar diameters from a series of photographs obtained from large-aperture ground-based telescopes. The series of photographs is processed to obtain the Weiner spectrum of the photographic image, i.e., the ensemble-averaged modulus-squared Fourier transform obtained from the series of images. Gezari, Labeyrie, and Stachnik have measured stellar diameters as small as 0″.05, about 20 times better than is usually possible. In this paper, mathematical expressions are obtained for the Wiener spectrum of the image of a point source. As is well known, the Wiener spectrum of the image of an extended, incoherently radiating object, is expressible as a product of this point-source spectrum and the object spectrum. Calculations are performed using the Rytov approximation and assuming that the underlying atmospheric turbulence is describable by a Kolmogorov spectrum. Asymptotic closed-form expressions are obtained for angular frequencies much less than, and much greater than, the conventional seeing limit. In the latter case, the Wiener spectrum is found to be proportional to the optical transfer function.

D. Korff

Papers

Analysis of a method for obtaining near-diffraction-limited information in the presence of atmospheric turbulence