A weather satellite monitors weather conditions on planet Earth.
Using infrared or visible radiation imagery techniques, these weather
satellites can detect clouds, snow and ice cover, fires, and city lights,
pollution, sand storms, ocean currents, and other environmental factors.
Infrared satellite imagery senses surface and cloud top temperatures
by measuring the wavelengths of electromagnetic radiation emitted
from these objects. High clouds are very cold, so they appear
white. Warmer, mid-level clouds will be light gray. Low
clouds, which are even warmer, appear dark gray or black. When
low clouds are actually the same temperature as the surrounding terrain,
they cannot be distinguished at all.
Visible satellite imagery uses reflected solar radiation (sunlight)
to distinguish objects in the atmosphere and on Earth's surface.
Clouds and fresh snow reflect sunlight well, so they appear white.
Clouds and snow can be differentiated because clouds move and snow does
not. Ground surfaces without snow cover reflect less sunlight, so
they appear black. This imagery cannot, of course, be used during
the night because it relies on reflections from the sun's rays.