GEOSTATIONARY SATELLITES

Besides collecting imagery, most environmental satellites perform additional functions. Some satellites contain communications packages designed to receive and relay signals between earth stations and other satellites and to collect and relay observation reports from automatic observation sites or buoys. Some satellites carry search and rescue (SAR) beacon locators. More advanced satellites carry sophisticated instruments known as "atmospheric sounders." These systems use infrared and microwave energy to provide vertical temperature and moisture profiles of earth’s atmosphere from the surface up to 30 miles. They also evaluate atmospheric stability. In addition, satellites can be used to measure a variety of other environmental parameters, such as sea surface temperature, wave height, snow/ice cover, low-level wind speed and direction, and ozone distribution. Although these functions are very important to meteorology and oceanography, you will not normally be involved in this type of data collection or data processing. In this module, we discuss only the differences in satellites that are important to you in acquiring satellite imagery. In the United States, both the U.S. Department of Commerce and the U.S. Department of Defense operate meteorological satellite programs. The National Oceanic and Atmospheric Administration (NOAA), a division under the Department of Commerce, operates its satellite programs through the National Environmental Satellite, Data, and Information Service (NESDIS). Their primary meteorological satellite programs are the Geostationary Operational Environmental Satellite (GOES), and the Advanced Television InfraRed Observation Satellite-NOAA (ATN) polar-orbiter (also called a TIROS-N or NOAA satellite). Both systems are energized with solar power while in orbit. The Department of Defense oversees the Defense Meteorological Satellite Program, usually referred to as the DMSP. GEOSTATIONARY SATELLITES Geostationary satellites are placed at an altitude (35,800 km) where their orbital period exactly matches the rotation of the earth. The satellite sensors scan the earth in horizontal lines, starting near the North Pole and working down towards the South Pole. Geostationary satellites are ideal for making large- scale, frequent observations of a fixed geographical area centered on the equator. Thus, they are better suited to track rapidly moving large-scale disturbances in the atmosphere, or to look closely at small-scale or short-duration changes in the atmosphere. However, their distance from the earth limits the resolution of the imagery. In addition, these satellites do not "see" the poles at all, and to achieve global coverage of just the equatorial regions, a network of 5 to 6 geostationary satellites is required. Figure 1-5 shows atypical GOES satellite. Figure 1-5.—GOES satellite. 1-5