Seeing Prevision—A Possible Application to the TNG Telescope at La Palma

Abstract

One of the most important problems for ground astronomy has always been the limiting resolution of the image imposed by the atmospheric turbulence in addition to the limit imposed by the optical instrument. The large diameters of the new generation telescopes increase the light collected by the instruments but can’t do anything to get a better spatial resolution in the image. The atmospheric turbulence modifies in a stochastic way the amplitude and the phase of the incoming wave front, and the images appear degraded. Different parameters are normally used to globally characterize the turbulence intensity in the atmosphere: Fried’s parameter r ₀, the seeing ∈, the C ²_n profiles, the outer scale L ₀, and the isoplanatic angles are only a sample of them. The seeing is universally used to characterize the image quality (Roddier et al., 1981), and it is defined as the width at the half height of a star image at the focus of a large diameter telescope. Now there are many reliable techniques and instruments (Sarazin and Roddier, 1990; Coulman, 1985) usually employed to measure the seeing. Direct or indirect methods are used to compute this parameter.