Scope and summary

This dissertation intends to describe and summarize in a comprehensive manner several studies, both theoretical and experimental, on the effects of seeing and wind turbulence associated with various types and configurations of telescope enclosures. The knowledge acquired on these effects will then be integrated into new methods and procedures for a global evaluation of telescope performance and will provide improved design guidelines for the project of future telescopes and their enclosures.

Therefore the scope of this dissertation is twofold:

1. A description of the effect of local atmospheric turbulence on the observation performance of astronomical optical telescopes. This description includes a number of new developments and experimental results which allow to get both useful engineering parameterizations and a global view and interpretation of these phenomena.

2. A contribution to the development of engineering criteria and guidelines, which draws the practical conclusions from the research results and which should assist the civil engineer assigned to the design of a telescope enclosure.

In the next chapter the main factors that influence the image quality of an astronomical telescope are summarized. The definitions underlying the seeing phenomenon are given together with its relationship with the temperature fluctuations of the atmosphere. One then introduces the errors caused by wind loading on the telescope: guiding errors due to vibrations of the telescope structures and dynamic deformations of the primary mirror. All these contributions are summarized in an error budget tree (fig. ).

Chapter describes the main requirements of telescope enclosures and outlines the concurrent engineering approach required to achieve an optimal design.
Through the description of history cases of telescope projects, we introduce the main issues and open questions related to local atmospheric turbulence and their consequences on the telescopes' performance and on the engineering of telescope enclosures. The last section of the chapter (§(, page ) summarizes these outstanding problems which constitute the main research object of the dissertation and are then expanded in the next chapters.

Chapter describes the aerodynamic environment surrounding a telescope. Two distinct aspects are studied by means of wind tunnel and full scale experiments: the first one concerns the characterization of the wind turbulence on the upper part of the telescope, which is responsible for high frequency guiding errors. The second aspect analyzed concerns the turbulent pressure fluctuations on the primary mirror and their relationship with optical aberrations.

In chapter we analyze the local seeing effects, due to refractive turbulent inhomogeneities of the atmosphere caused by the telescope and by the observatory itself. The various contributions from the primary mirror of the telescope, the enclosure and the atmospheric surface layer are elucidated by means of experimental measurements, theoretical analysis and numerical simulations.

Chapter introduces a systems engineering approach in which the different contributions to the telescope image quality can be combined for a global evaluation of performance of the telescope and the influence of the enclosure.