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NOAA's Geostationary and Polar-Orbiting Weather Satellites

Operating the country's system of environmental ( weather ) satellites is one of the major responsibilities of the National Oceanic and Atmospheric Administration's (NOAA's) National Environmental Satellite, Data, and Information Service (NESDIS). NESDIS operates the satellites and manages the processing and distribution of the millions of bits of data and images theses satellites produce daily. The primary customer is NOAA's National Weather Service, which uses satellite data to create forecasts for the public, television, radio, and weather advisory services. Satellite information is also shared with various Federal agencies, such as the Departments of Agriculture, Interior, Defense, and Transportation; with other countries, such as Japan, India, and Russia, and members of the European Space Agency (ESA) and the United Kingdom Meteorological Office; and with the private sector.

NOAA's operational weather satellite system is composed of two types of satellites: geostationary operational environmental satellites (GOES) for short-range warning and "now-casting" and polar-orbiting satellites for longer-term forecasting. Both types of satellite are necessary for providing a complete global weather monitoring system.

A new series of GOES and polar-orbiting satellites has been developed for NOAA by the National Aeronautics and Space Administration (NASA). The new GOES-I through M series provide higher spatial and temporal resolution images and full-time operational soundings (vertical temperature and moisture profiles of the atmosphere). The newest polar-orbiting meteorological satellites (that began with NOAA-K in 1998) provide improved atmospheric temperature and moisture data in all weather situations. This new technology will help provide the National Weather Service the most advanced weather forecast system in the world.

Geostationary Operational Environmental Satellites (GOES)

GOES satellites provide the kind of continuous monitoring necessary for intensive data analysis. They circle the Earth in a geosynchronous orbit, which means they orbit the equatorial plane of the Earth at a speed matching the Earth's rotation. This allows them to hover continuously over one position on the surface. The geosynchronous plane is about 35,800 km (22,300 miles) above the Earth, high enough to allow the satellites a full-disc view of the Earth. Because they stay above a fixed spot on the surface, they provide a constant vigil for the atmospheric "triggers" for severe weather conditions such as tornadoes, flash floods, hail storms, and hurricanes. When these conditions develop the GOES satellites are able to monitor storm development and track their movements.

GOES satellite imagery is also used to estimate rainfall during the thunderstorms and hurricanes for flash flood warnings, as well as estimates snowfall accumulations and overall extent of snow cover. Such data help meteorologists issue winter storm warnings and spring snow melt advisories. Satellite sensors also detect ice fields and map the movements of sea and lake ice.

NASA launched the first GOES for NOAA in 1975 and followed it with another in 1977. Currently, the United States is operating GOES-10 and GOES-12. (GOES-9, which is partially operational, is being provided to the Japanese Meteorological Agency to replace their failing geostationary satellite.) GOES-11 is being stored in orbit as a replacement for GOES-12 or GOES-10 in the event of failure failure.

GOES-10 and GOES-12
The United States normally operates two meteorological satellites in geostationary orbit over the equator. Each satellite views almost a third of the Earth's surface: one monitors North and South America and most of the Atlantic Ocean, the other North America and the Pacific Ocean basin. GOES-12 (or GOES-East) is positioned at 75 W longitude and the equator, while GOES-10 (or GOES-West) is positioned at 135 W longitude and the equator. The two operate together to produce a full-face picture of the Earth, day and night. Coverage extends approximately from 20 W longitude to 165 E longitude. This figure shows the coverage provided by each satellite.

The main mission is carried out by the primary instruments, the Imager and the Sounder. The imager is a multichannel instrument that senses radiant energy and reflected solar energy from the Earth's surface and atmosphere. The Sounder provides data to determine the vertical temperature and moisture profile of the atmosphere, surface and cloud top temperatures, and ozone distribution.

Other instruments on board the spacecraft are a Search and Rescue transponder, a data collection and relay system for ground-based data platforms, and a space environment monitor. The latter consists of a magnetometer, an X-ray sensor, a high energy proton and alpha detector, and an energetic particles sensor. All are used for monitoring the near-Earth space environment or solar "weather." GOES-12, the newest satellite also carries a Solar X-Ray Imager (SXI).

The United States reaps many benefits from the new series of GOES satellites as they aid forecasters in providing better advanced warnings of thunderstorms, flash floods, hurricanes, and other severe weather. The GOES-I series provide meteorologists and hydrologists with detailed weather measurements, more frequent imagery, and new types of atmospheric soundings. The data gathered by the GOES satellites, combined with that from new Doppler radars and sophisticated communications systems make for improved forecasts and weather warnings that save lives, protect property, and benefit agricultural and a variety of commercial interests.

For users who establish their own direct readout receiving station, the GOES satellites transmit low resolution imagery in the WEFAX service. WEFAX can be received with an inexpensive receiver. Highest resolution Imager and Sounder data is found in the GVAR primary data user service which requires more complex receiving equipment. More information about establishing receiving stations can be obtained from the Email contact at the bottom of the page.

For more detailed information about the GOES satellites, see the GOES I-M DataBook, Revision 1, published 4 January 1997 by Space Systems-Loral. The most recent pictures received from the directly from the NOAA GOES satellites can be found at the NOAA GOES Server.

Polar-Orbiting Satellites

Complementing the geostationary satellites are two polar-orbiting satellites known as Advanced Television Infrared Observation Satellite (TIROS-N or ATN), constantly circling the Earth in an almost north-south orbit, passing close to both poles. The orbits are circular, with an altitude between 830 (morning orbit) and 870 (afternoon orbit) km, and are sun synchronous. One satellite crosses the equator at 7:30 a.m. local time, the other at 1:40 p.m. local time. The circular orbit permits uniform data acquisition by the satellite and efficient control of the satellite by the NOAA Command and Data Acquisition (CDA) stations located near Fairbanks, Alaska and Wallops Island, Virginia. Operating as pair, these satellites ensure that data for any region of the Earth are no more than six hours old.

A suite of instruments is able to measure many parameters of the Earth's atmosphere, its surface, cloud cover, incoming solar protons, positive ions, electron-flux density, and the energy spectrum at the satellite altitude. As a part of the mission, the satellites can receive, process and retransmit data from Search and Rescue beacon transmitters, and automatic data collection platforms on land, ocean buoys, or aboard free-floating balloons. The primary instrument aboard the satellite is the Advanced Very High Resolution Radiometer or AVHRR.

Data from all the satellite sensors is transmitted to the ground via a broadcast called the High Resolution Picture Transmission (HRPT). A second data tranmission consists of only image data from two of the AVHRR channels, called Automatic Picture Transmission (APT). For users who want to establish their own direct readout receiving station, low resolution imagery data in the APT service can be received witn inexpensive equipment, while the highest resolution data transmitted in the HRPT service utilizes a more complex receiver. Additional information about establishing receiving station can be obtained from the Email contact below.

The polar orbiters are able to monitor the entire Earth, tracking atmospheric variables and providing atmospheric data and cloud images. They track weather conditions that eventually affect the weather and climate of the United States. The satellites provide visible and infrared radiometer data that are used for imaging purposes, radiation measurements, and temperature profiles. The polar orbiters' ultraviolet sensors also provide ozone levels in the atmosphere and are able to detect the "ozone hole" over Antarctica during mid-September to mid-November. These satellites send more than 16,000 global measurements daily via NOAA's CDA station to NOAA computers, adding valuable information for forecasting models, especially for remote ocean areas, where conventional data are lacking.

Currently, NOAA is operating five polar orbiters. A new series of polar orbiters, with improved sensors, began with the launch of NOAA-15 in May 1998 and NOAA-16 on September 21, 2000. The newest, NOAA-17, was launched June 24, 2002.  NOAA-12, NOAA-14 and NOAA-15 all continue transmitting data as stand-by satellites. NOAA-16 and NOAA-17 are classified as the "operational" satellites.

Find out about the first United States weather satellite launched in 1960. For more technical information on the NOAA polar-orbiting satellites, see the NOAA-KLM User's Guide, and the NOAA - L Advanced TIROS-N (ATN) Pamphlet. Link to the USGS site for more information about the AVHRR instrument.

How Satellites Are Named
NOAA assigns a letter to the satellite before it is launched, and a number once it has achieved orbit. For example, GOES-H, once in orbit, was designated GOES-7, GOES-G, which was lost at launch, was never assigned a number. The same system is used for polar orbiters; for example, NOAA-11, still in orbit, was designated NOAA-H before launch. NOAA-J became NOAA-14.

Additional Links to Information
Other sites to visit: NASAs GOES Project Office and POES Project Office. Find out about the U.S. military metorological satellite, DMSP. Examples of NOAA polar orbiting satellite imagery of significant weather events can be found at the JHU Applied Physics Laboratory web site. A collection of pictures (NOAA in Space) related to NOAA satellites can be found at the NOAA Library.

There is a brief history of the GOES satellites from NASA. Florida State University has a history of many of the NOAA satellites and details of when they were launched.

Other United States and Non-U.S. Satellites
Many other environmental satellites are operated by nations, international organizations and commercial enterprises. Below are links to more information to a sampling of these other satellite systems.

• METEOSAT, the European geostationary satellite from the ESOC site; also, learn about METEOSAT Second Generation (MSG).
  
• METEOR-- Russia's polar orbiting satellites: METEOR-3/TOMS (Total Ozone Mapping Spectrometer) data archive, 1991-1994. General METEOR APT information note.
  
• Landsat, a high resolution Earth observation satellite managed by NASA and the USGS.
  
• SeaWiFs oceanographic satellite.
  
• Earth Observation Satellite EOS Terra.
  
• METOP, the European polar-orbiter to be launched in 2005.
  
• RADARSAT: Canada's Satellites
  
• MOS-1,1b, JERS-1, ADEOS, GMS: Japan's Satellites

[NOTICE: When following some of the links listed above, you will leave the NOAASIS web site and the NOAA domain. We provide these links since the information may be of interest to our users. However, NOAA does not necessarily endorse the content of any of these sites.]

Revised: 21 November 2003