Atmospheric optical links are particularly affected by weather conditions. In this article, visibility and attenuation have been recorded over a distance for a terrestrial free space optical link operating with a 780 nm wavelength. This paper has shown the experimental optical link attenuation measurements results performed for visibilities ranging from 9-12 km. The existing models showing the relationship between atmospheric visibility and optical attenuation do not match well if compared with recorded data. Appropriate expressions which has consolidated Kruse attenuation model have been derived. The comparison of the corrected model to field data has shown the accuracy of the proposed modification.