A foghorn or fog signal is a device that uses sound to warn vehicles of navigational hazards such as 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.
Building housing the two diaphone foghorns at Split Rock Light.
An early form of fog signal. The fog bell at Fort Point Light Station, Maine.
Foghorn at the Lizard Lighthouse, Cornwall. This installation uses a siren to produce sound.
Another Trinity House fog siren installation on Flat Holm, now restored by the Flat Holm Project
Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influenced by nearby bodies of water, topography, and wind conditions. In turn, fog affects many human activities, such as shipping, travel, and warfare.
Light fog in Bangladesh
Minute droplets of water constitute this after-dark radiation fog, with an ambient temperature of −2 °C (28 °F). Their motion trails are captured as streaks.
A close-up view of water droplets forming fog. Those outside the camera lens's depth of field appear as orbs.
Advection fog layer in San Francisco with the Golden Gate Bridge and skyline in the background
