Fog dispersal is the process of clearing or dissipating fog, often artificially, to improve visibility, particularly for aviation and transportation. It's essentially any method used to make fog less dense or to remove it altogether from a specific area. The goal is to make conditions safer for activities that are hindered by poor visibility due to fog.
Methods of Fog Dispersal
Several techniques exist to disperse fog, although their practicality and effectiveness vary depending on the type of fog, weather conditions, and the scale of the area needing to be cleared. These methods can be broadly categorized as follows:
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Heating: Warming the air can increase evaporation and reduce the relative humidity, causing the fog to dissipate. This method is typically localized and may be implemented using powerful heaters or burners.
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Seeding: Introducing hygroscopic materials (materials that attract water) into the fog can cause water droplets to coalesce and grow large enough to fall as drizzle or rain, thereby clearing the fog. Silver iodide and other salts are often used for seeding.
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Mixing: Forcing drier air to mix with the fog can lower the humidity and cause the fog to evaporate. This can be achieved through mechanical means, such as large fans or downdraft-inducing aircraft.
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Fog Collection: This involves physically capturing the water droplets in the fog using nets or other structures. This method is more about harvesting water from fog than dispersal for visibility, but it does reduce the fog density in the immediate vicinity of the collectors.
Fog Investigation and Dispersal Operation (FIDO)
During World War II, a particularly notable fog dispersal system called Fog Investigation and Dispersal Operation (FIDO), sometimes referred to as "Fog Intense Dispersal Operation" or "Fog, Intense Dispersal Of," was developed to allow aircraft to land safely in dense fog and smog. FIDO worked by creating a large, open fire along the runway, which warmed the air and evaporated the fog directly above the landing strip. While effective, it was resource-intensive and environmentally impactful.
Current Applications
Modern fog dispersal efforts are largely focused on aviation. Airports sometimes employ ground-based heating systems, seeding techniques, or improved weather forecasting to mitigate the impact of fog on flight operations. The environmental impact and cost-effectiveness of each method are carefully considered.
