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The increasing need for high throughput and security in ground-satellite links is fostering the development
of optical telecommunication solutions to compensate for the atmospheric turbulence by adaptive optics (AO).
In the case of a Low-Earth Orbit (LEO) satellite, it is crucial to maximize the duration of the downlink, even
at low elevations, since a satellite spends half of the time it is viewable by a ground station between 30° and
10° elevations. However, as the elevation decreases, the path of the beam through the atmosphere gets longer,
and the perturbations in the pupil of the receiver terminal get stronger. This is all the more noticeable as we go
from a weak perturbation regime to a strong perturbation regime. This is a critical issue for AO systems since
an inhomogeneous distribution of intensity leads to a reduced performance of the wavefront sensor (WFS) and
thus hinders the correction. Regarding the Shack-Hartmann wavefront sensor (SHWFS), scintillation induces
a wide signal range between the various subapertures causing part of them to be saturated and others to be
extinguished. Besides, some subapertures spots suffer from strong diffraction effects induced by non-uniform
intensity distribution, making it difficult to obtain accurate centroid measurements. We propose here to study the
effect of the number of subapertures of a SHWFS on its performance in the presence of amplitude perturbations
representative of a LEO to ground link. We show preliminary results –while neglecting noise and dynamic
range limitations– leading to the conclusion that increasing the SHWFS sampling of the pupil plane improves
its robustness to scintillation.
