Experimental analysis of image quality for an horizontal overwater propagation

The effect of atmospheric turbulence on the imaging of scenes, for an horizontal propagation of the light over a distance of 20 km, 15 meters above the sea surface, was analyzed at visible wavelength using a 20 cm telescope. Point-sources images were recorded during the night, and the Fried parameter r 0 was derived leading to values ranging from 1.5 to 3.6 cm. A very high level of scintillation was observed. Studies of correlations between close-by sources lead to a very small domain of isoplanatism. Daytime observations of an extended source are also performed; an image motion of small spatial coherent length seems to be drawn by an horizontal wind producing wave-like distortion of horizontal lines and boiling-like of vertical ones.