Geostationary Operational Environmental Satellites (GOES) satellites are a mainstay of weather forecasting for the National Weather Service. Satellite images you see on the nightly TV weathercast are from GOES satellites.
The United States operates two meteorological satellites in geostationary orbit, one over the equator at 75°W with a view of the East Coast and the other over the equator at 135°W for the West Coast view. At right, are the the views from each satellite. Click images to enlarge.
Since the satellites are positioned over the equator, they are viewing the northern hemisphere at an angle so you can get a sense of the vertical development of the clouds. Also taller clouds will cast shadows onto lower ones so visible imagery is an excellent tool for locating developing thunderstorms.
However, computer enhancements of these images are common. Probably the most common enhancement is combining both GOES West and East into one image of the continental U.S. and changing the perspective (right).
This view (the same time frame as the two above full disk views) has been enhanced to color the surface of the earth as well change the perspective to make it appear the satellite is directly over the center of the U.S.
These satellites are capable of providing information on clouds and moisture in three primary forms - visible, infrared (IR), and water vapor imagery.
- Visible imagery
- Visible imagery is just like the name suggests; an image of the earth in visible light. This is a similar manner to that of a person taking a picture with a camera. The satellite detects sunlight reflected from objects within the viewfinder. In the case of the satellite, the objects are the upper surfaces of clouds. Thick clouds do a much better job of reflecting light and therefore appear brighter in visible photos.
With the satellites positioned over the equator, they view the northern hemisphere at an angle so you can get a sense of the vertical development of the clouds. Also taller clouds will cast shadows onto lower ones so visible imagery is an excellent tool for locating developing thunderstorms.
- Infrared imagery
- The obvious problem with visible imagery is that it is only available during the day. To combat this problem, the infrared (IR) sensor was devised. It senses radiant (heat) energy given off by the clouds. Warmer (lower in the atmosphere) clouds give off more energy than cold (higher) clouds. The IR sensor measures the heat and produces several images based upon different wavelengths in the IR range of the electromagnetic spectrum.
Often these images are color enhanced to help better distinguish the taller (coldest, usually from thunderstorms) cloud tops.
- Water vapor imagery
- Water vapor imagery is unique in that it can detect water vapor (water in a gas state) in addition to clouds. However, due to absorption of energy by the atmosphere this view only "sees" the top third of the troposphere. While the low level moisture is hidden from the satellite sensor, the upper level moist/dry areas is plainly observable. Moist areas show up as white and dry areas as black.