Besides collecting imagery, most environmentalsatellites perform additional functions. Somesatellites contain communications packages designedto receive and relay signals between earth stations andother satellites and to collect and relay observationreports from automatic observation sites or buoys.Some satellites carry search and rescue (SAR) beaconlocators. More advanced satellites carry sophisticatedinstruments known as "atmospheric sounders." Thesesystems use infrared and microwave energy to providevertical temperature and moisture profiles of earth’satmosphere from the surface up to 30 miles. They alsoevaluate atmospheric stability. In addition, satellitescan be used to measure a variety of otherenvironmental parameters, such as sea surfacetemperature, wave height, snow/ice cover, low-levelwind speed and direction, and ozone distribution.Although these functions are very important tometeorology and oceanography, you will not normallybe involved in this type of data collection or dataprocessing. In this module, we discuss only thedifferences in satellites that are important to you inacquiring satellite imagery.In the United States, both the U.S. Department ofCommerce and the U.S. Department of Defenseoperate meteorological satellite programs. TheNational Oceanic and Atmospheric Administration(NOAA), a division under the Department ofCommerce, operates its satellite programs through theNational Environmental Satellite, Data, andInformation Service (NESDIS). Their primarymeteorological satellite programs are theGeostationary Operational Environmental Satellite(GOES), and the Advanced Television InfraRedObservation Satellite-NOAA (ATN) polar-orbiter(also called a TIROS-N or NOAA satellite). Bothsystems are energized with solar power while in orbit.The Department of Defense oversees the DefenseMeteorological Satellite Program, usually referred toas the DMSP.GEOSTATIONARY SATELLITESGeostationary satellites are placed at an altitude(35,800 km) where their orbital period exactly matchesthe rotation of the earth. The satellite sensors scan theearth in horizontal lines, starting near the North Poleand working down towards the South Pole.Geostationary satellites are ideal for making large-scale, frequent observations of a fixed geographicalarea centered on the equator. Thus, they are bettersuited to track rapidly moving large-scale disturbancesin the atmosphere, or to look closely at small-scale orshort-duration changes in the atmosphere. However,their distance from the earth limits the resolution of theimagery. In addition, these satellites do not "see" thepoles at all, and to achieve global coverage of just theequatorial regions, a network of 5 to 6 geostationarysatellites is required. Figure 1-5 shows atypical GOESsatellite.Figure 1-5.—GOES satellite.1-5
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