Propagation of optical flat-topped Gaussian beams in earth-satellite optical communication links is investigated where part of the link is turbulent atmosphere. Flat-topped Gaussian source field is obtained by superposing many Gaussian beams of different source size. Starting with the flat-topped Gaussian incidence at the earth surface, the average intensity at the satellite is formulated by using the extended Huygens Fresnel principle. For the structure constant variation versus height, Hufnagel-Valley model is employed in the vertical and slant paths. The received average intensity is numerically calculated and the effects of the source and medium parameters on the received average intensity profile are examined for different zenith angles. In earth-satellite optical communications links, the advantages of using flat-topped Gaussian beams as compared to Gaussian beams are scrutinized.