Belonging to the group of the photometeors, mirages are due to the curving of light rays passing through layers of air in which the refractive index changes considerably with height as a result of differences in density. They are therefore generally observed when the temperature of the Earth's surface differs markedly from that of the air above. A mirage may occur as a lower mirage over intensely heated surfaces (often seen on roads) or as upper mirage over cold surfaces. Latter case, also called superior mirror effect, is less common and the objects at the horizon are loomed and sometimes turned upside down.

The picture was taken on a hot summer day at the coast in which the air temperature did rise above 35°C. Just above the relative cold sea surface the superior mirror effect became visible and the ships on the horizon are floating in the air as upside down images.