Presentation 1 : Poster
wavefront deformations retrieval for solar observation
M.Chibani, A.Irbah, J.Borgnino, F.Martin
The ground-based astronomical observations, especially for solar diameter measurement, suffer from the distortion of the wave-front phase that is caused by the atmospheric turbulence. Borgnino & al. proposed a technique that permits the measure of the turbulence parameters by observing the solar limb. A diaphragm is put at the focal plan of the main lens, then a second lens is used to obtain the pupil plan image. The diaphragm causes a spatial filtering, this effect combined with the assumption that the solar limb is mostly linear for a small angle, leads to an expression that links the intensity fluctuations observed on the pupil plan with the phase of the wave-front. Using the technique aforementioned we shall, at a first stage, measure the temporal parameters related to the wave-front.
The diaphragm introduces two kinds of filtering; the first one is the diffraction effect that depends only on the diaphragm’s aperture. The second one is the integration effect that depends both upon the diaphragm’s aperture and the turbulent layers altitude. Thus, we ought to choose a diaphragm’s aperture that makes the measurement as independent as possible on the layers altitude.
The simulations we made show that this technique is completely suitable for turbulence parameters measurement in case of solar observation and that regardless of the filtering effect introduced by the diaphragm.