GOES visible (or “sun-lit”) image GOES Satellite The GOES (Geostationary Operational Environmental Satellite) Imager scans the earth to build images with spectral frequencies in the visible and infrared wavelengths. The satellite orbits the earth at approximately 36,000 km--22,300 miles-- (about a tenth of the distance to the moon). This geostationary orbit (with a period of 24 hours) allows continuous observation of the same region on the earth. For GOES, the western hemisphere. Why? Because the geostationary satellites orbit the Earth's axis as fast as the Earth spins. The GOES is operated by the National Oceanic and Atmospheric Administration (NOAA) /National Environmental Satellite, Data, and Information Service (NESDIS). The configuration has typically included GOES-East scanning eastern North America, South America, and the western Atlantic Ocean (at longitude 75 West) and GOES-West scanning western North America and the eastern Pacific Ocean (at Longitude 135 West). These images are from the eastern GOES. These images are all from 18 UTC (noon Central) on March 6, 2003. Most satellite images seen on the local television news or the Weather Channel are produced by GOES satellites. GOES visible (or “sun-lit”) image The visible image shows reflected sunlight in the visible part of the electro-magnetic spectrum. A visible satellite image represents sunlight scattered by objects suspended in the atmosphere or on Earth. Visible images are only available during the day. Differences in the reflected radiation of clouds, water, land, and vegetation allow differentiating these features in the imagery. Dark areas in a visible satellite image represent geographic regions where only small amounts of visible sunlight are reflected back to space. The oceans are usually dark while highly reflective surfaces, like snow and thick clouds are bright. The visible data are useful for cloud, haze detection and severe storm identification. GOES infrared window or “heat” image This infrared image measures the heat of the emitted surface. These images are available both during the day and night. All objects emit radiation related to their temperature and their ability to emit radiation. This infrared (IR) band provides information on the temperature of land, water, and clouds by measuring the infrared radiation emitted from surfaces below the satellite. The radiant energy measured by infrared radiometers is converted to a temperature. Cold surfaces are color-coded to be white, while hot surfaces are displayed as dark shades. Cold clouds are displayed as white shades, while warmer clouds are shades of gray. The hot land surfaces are shown in black. The infrared band is used to determine cloud-drift winds, severe storm identification, and location of heavy rainfall. GOES Water Vapor image Water vapor is transparent to radiation at visible and IR wavelengths. This is why visible and IR satellite imagery are used to observe surface features and clouds. However, water vapor is a very efficient absorber and emitter of radiation with wavelengths near 6.7 μm. So, satellite radiometers measuring the amount of radiation emitted by the atmosphere at these wavelengths can be used to detect water vapor in the atmosphere. The water vapor satellite image displays the water vapor concentration in the middle and upper parts of the troposphere, a key region for storm development and growth. Clouds appear white, while the dark regions denote drier air or “jet streaks.” The GOES “water vapor” imagery is useful for estimating regions of mid-level moisture content and tracking mid-level atmospheric motions. UW CIMSS / NOAA NESDIS