Tracking Fog from Space

Hong Kong is shrouded in fog yesterday (6 March 2006) and today (7 March 2006) as a moist maritime airstream affected the region. The lowest visibility this morning was only 200 metres. With the use of weather satellite, it is possible to locate the fog from space.

During the day, fog can be observed with the naked eye. At night, however, observation of fog can prove to be a difficult task, particularly when there is no light around. The Hong Kong Observatory receives and processes satellite images from the Earth Observing Satellites (EOSs) to assist weather forecasters in monitoring of fog around Hong Kong. The sensors onboard the EOSs take images of the earth using a number of infrared channels. After special processing of the satellite images, the location of fog can be highlighted in colour (Figure 1).

A few examples of fog episodes in 2006 can be found in the satellite gallery on the Hong Kong Observatory's website, which is accessible at
http://www.weather.gov.hk/en/wxinfo/intersat/satellite_gallery/index.htm.

Figure 1 Image captured by the Earth Observing Satellite of NASA at 11 p.m. on 6 March 2006. Fog (in red colour) shrouded the Pearl River Delta and the neighbouring waters.