NOAA's Geostationary and Polar-Orbiting Weather Satellites

Operating the country's system of environmental satellites is one of the major responsibilities of the National Oceanic and Atmospheric Administration, NOAA's National Environmental Satellite, Data, and Information Service (NESDIS) operates the satellites and manages the processing and distribution of the millions of bits of data and images theses satellites produce daily. The prime customer is NOAA's National Weather Service, which uses satellite data to create forecasts for 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 kinds of satellite are necessary for providing a complete global weather monitoring system.

A new series of GOES and polar-orbiting satellites is being developed for NOAA by the National Aeronautics and Space Administration (NASA). The new GOES-I will provide higher spatial and temporal resolution images and full-time operational soundings. The polar-orbiting meteorological satellites will provide improved atmospheric temperature and moisture data in all weather situations. This new technology will give the National Weather Service the most advanced weather forecast system in the world.

Geostationary Operational Environmental Satellites (GOES)

GOES satellite 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 atmospheric "triggers" for severe weather conditions such as tornadoes, flash floods, hail storms, and hurricanes. When these conditions develop the GOES satellite monitor storms 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-7, which is supported by Europe's Meteosat-3, and will launch GOES-I in April 1994 and GOES-J in 1995.

GOES-7, Meteosat-3, and GOES-I

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. The two operate together to send a full-face picture of the Earth, day and night. However, with the failure of the GOES-6 in 1989, the United States had only one operational satellite, GOES-7, which was repositioned midway over the United States.

In August 1991, Meteosat-3 was moved from 5 degrees West to 50 degrees West over the equator to supplement NOAA's GOES system. In February 1993, it was moved to 75 degrees West Meteosat-3 was launched in 1988 and served as Europe's operational satellite until June 1989 when it was replaced by Meteosat 4. It was developed for and operated by, the ESA on behalf of the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT).

The United States will reap many benefits from the April 1994 launch of GOES-I as it begins to aid forecasters in providing better advanced warnings of thunderstorms, flash floods, hurricanes, and other severe weather. Improved forecasts will save lives, preserve property, and benefit agricultural and commercial interests.

The GOES-I will provide meteorologists and hydrologists with detailed weather measurements, more frequent imagery, and new types of atmospheric soundings. The data gathered by GOES-I, combined with that from new Doppler radars, will make possible a revolutionary flood and water management system devised by National Weather Service hydrologists, greatly aiding water resource managers as they make critical decisions about allocating precious water resources, particularly those of the western states.

Polar-Orbiting Satellites

Complementing the geostationary satellites are two polar- orbiting satellites known as advanced Television Infrared Observing System (TIROS) satellites. Constantly circling the Earth in an almost north-south orbit, passing close to both poles. One crosses the equator at 7:30 a.m. local time, the other at 1:40 p.m. local time. Operating as pair, these satellites ensure that data for any region of the Earth are no more than six hours old.

The polar orbiters monitor the entire Earth, tracking atmospheric variables and providing atmospheric data and cloud images. They track weather patterns that 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 to NOAA's Command and Data Acquisition (CDA) station computers, adding valuable information for forecasting models, especially for remote ocean areas, where conventional data are lacking.

Currently, NOAA is operating two polar orbiters: NOAA-11, launched in September 1988, and NOAA-12, launched in May 1991. NOAA-J is scheduled for launch in late 1994, with follow-on models launched as needed in subsequent years.

How Satellites Are Names

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, now in orbit, was designated NOAA-H before launch.