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Diameter measurements performed with the so- lar astrolabe are aected by instrumental and atmospheric eects. The problem is to know how these eects con- tribute to the error on diameter measurements. Thus, a numerical simulation is developed to bring some responses to this problem. For this purpose, synthetic images of the Sun similar to the ones obtained by the instrument through the Earth atmosphere are simulated. A fractal model is used to generate randomly perturbed wavefronts and therefore optical response of the whole system, at- mosphere and instrument. Many sequences of solar im- ages are then simulated for various observation conditions (Fried's parameterr0, spatial coherence outer scale L0 and atmospheric characteristic times). They are used to dene the time of contact of the direct and reflected solar im- ages which is fundamental in the solar astrolabe experi- ment. It is then studied as a function of the observation conditions relatively to the experimental characteristics (exposure time).

Error due to atmospheric turbulence effects on solar diameter measurements performed with an astrolabe