terça-feira, 3 de fevereiro de 2009
These images come from satellites which remain above a fixed point on the Earth (i.e. they are "geostationary"). The visible images record visible light from the sun reflected back to the satellite by cloud tops and land and sea surfaces. They are equivalent to a black and white photograph from space. They are better able to show low cloud than infrared images (low cloud is more reflective than the underlying land or sea surface). However, visible pictures can only be made during daylight hours.
Coast-lines and lines of latitude and longitude have been added to the images and they have been altered to polar stereographic projection.
The visible images are updated every hour. It usually takes about 20 minutes for these images to be processed and be updated on the web site. The time shown on the image is in UTC.