Since clouds are excellent reflectors of light, they appear white, while land masses and water of the oceans appear darker. Satellites broadcast the visible data to earth where a black and white photograph is constructed. Visible images show the daytime cloud cover on earth, and they assist with the mapping of ice within the shipping channels of the polar regions and the Great Lakes. Visible images also detect valuable data about Northern Hemisphere snow cover and monitor the conditions of vegetation. Polar orbiting satellites record the global data they collect and broadcast the data as they pass over one of the two receiving stations located in Alaska and Virginia.
Satellites can provide an image of the weather day or night, when sunlight is no longer available.
These images are called infrared. Chances are, images seen on the late evening television weather broadcast are infrared images. The earth radiates heat into space all the time. Infrared imagery shows different temperatures in black, white and shades of grey. The coldest temperatures show up as white and warmest as black.