The international definition of fog consists of a collection of suspended water droplets or ice crystals near the Earth’s surface that lead to a reduction of horizontal visibility below 1 km (5/8 of a statute mile) (NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, 1995). If the visibility is greater than 1 km, then it is called mist (WMO, 1966). Prevailing visibility is the maximum visibility value common to sectors comprising one-half or more of the horizon circle (MANOBS, 2006). Water droplets and ice crystals, typically 5 to 50 lm in diameter (PRUPPACHER and KLETT, 1997), form as a result of supersaturation generated by cooling, moistening and/or mixing of near surface air parcels of contrasting temperatures. The presence of suspended droplets and/or crystals can render an object undistinguishable to a distant observer and thus causes poor visibility conditions.