Sounding the Sumburgh Foghorn

Scotland, UK. A foghorn is a fog signal that uses sound to warn vehicles of navigational hazards like rocky coastlines or boats of the presence of other vessels, in foggy conditions.

The term is most often used in relation to marine transport. When visual navigation aids such as lighthouses are obscured, foghorns provide an audible warning of rock outcrops, shoals, headlands, or other dangers to shipping.