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As the April 11, 1965 , Palm Sunday tornado outbreak devastated parts of four midwestern states, the NOAA Weather Service (NWS) forecasters tracked storms with surveillance equipment that today would be termed rudimentary at best.

Advances in electronics and related technologies over the ensuing years have proven to be a boon for agency forecasters in their efforts to save lives and prevent property damage. The rise of Doppler radar and weather satellites opened the doors for the massive amounts of data deciphered by today’s forecasters to give timely and accurate forecasts and warnings.

Radar Technology and Weather Service Modernization

Weather Service radar operators on April 11, 1965, could see only green blobs on their radar scopes and were required to have visual confirmation from the ground to issue tornado “alerts.” Radars were scattered across the country, with large areas not served at all, in a combination of "network" and "local warning" radars. Operators were able to tell where a storm system was located, but only the most experienced could provide much detail about a given storm.

The multi-billion dollar NWS modernization of the 1990s brought state-of-the-art technologies to both radar and satellite programs. Doppler radar and weather satellites in geosynchronous orbit of the Earth provided forecasters with the tools needed to take weather warning capabilities to new levels.

As the 1950s radars (as well as some upgraded in the 1970s) approached obsolescence, the NWS joined the Department of Defense and the Department of Transportation (specifically the Federal Aviation Administration) to create design parameters for a new generation of Doppler weather radars that are able to see inside storm systems and better track their motion. The Weather Surveillance Radar 1988 Doppler (WSR-88D) was designed specifically to monitor weather systems and tie into modern computer systems that turned technological dreams of the 1960s into routine surveillance in the 21st Century.

Employing the Doppler effect to track frequencies of winds moving toward the radar and winds moving away from the radar, the WSR-88D observes the presence and calculates the speed and direction of motion of severe weather elements such as tornadoes and thunderstorms. The WSR-88D provides quantitative area precipitation measurements, important in hydrologic forecasting of potential flooding. The severe weather and motion detection capabilities contribute to improved accuracy and timeliness of NWS warnings. The technology has helped the NWS increase tornado warning lead times; improve the detection and measurement of damaging winds, severe turbulence, wind shear and hail associated with severe thunderstorms; improve forecasts of the location and severity of thunderstorms; and improve the accuracy in identifying threatened areas and substantially reduced the number of false alarms.

Radar detects the presence and location of an object by bouncing an electromagnetic signal off of it and measuring the time it takes for the signal to return. This measurement is used to determine the distance and direction of the object from the radar, such as particles of water, ice or dust in the atmosphere. Radar signals reflected from a moving object undergo a change in frequency related to the speed of the object traveling toward or away from the radar antenna. The return signal is different for objects moving away from the radar and objects moving toward the radar.

The WSR-88D detects two motions associated with clouds. The radar calculates both the speed and direction of motion of a severe storm. It also detects internal motions of the storm and certain unique internal motions can be a precursor of tornado formation. For example, a developing tornado can be detected forming above the Earth before it reaches the ground. This means earlier detection of the precursors to tornadoes, as well as data on the direction and speed of tornadoes once they form.

As part of the 1990s modernization, the NWS, the Department of Defense and the FAA deployed more than 160 radars across the country. The integrated network of radars with overlapping coverage of the entire United States and its island territories from Guam to Puerto Rico dramatically enhanced the NWS’ ability to safeguard life, property and commerce.

Satellites Boost Weather Surveillance

Modern-day weather satellites play their own important role in tracking severe weather. In 1965, the first satellite created for weather surveillance was still two years from reality. Those early satellites bore little resemblance to the geostationary satellites that provide images seen daily on television weather casts across the country today.

The first weather satellite, designated the Applications Technology Satellite 3 (ATS 3), was launched Nov. 5, 1967. The ATS 3 was a set of six NASA spacecraft created to explore and flight-test new technologies and techniques for communications, meteorological and navigation satellites. The major objective of the early ATS satellites was to test whether gravity would anchor the satellite in a synchronous orbit (22,300 miles above the earth), allowing it to move at the same rate the Earth turns, thus seeming to remain stationary. The tested satellites also collected and transmitted meteorological data and functioned, at times, as communications satellites to the Pacific Basin and Antarctica . ATS satellites provided the first color images from space as well as regular cloud cover images for meteorological studies.

Synchronous Meteorological Satellites

To provide improved meteorological data on worldwide weather phenomena for improved forecasting, NASA launched two Synchronous Meteorological Satellites (SMS): SMS 1 was launched May 17, 1974, and SMS 2 was launched Feb. 6, 1975. After the SMS 2 launch, NASA turned over the geostationary satellite program to NOAA for operation. NOAA acquired additional spacecraft identical to SMS and gave them the new name Geostationary Operational Environmental Satellite (GOES). The SMS series included the first operational satellite in the NOAA system.

Geostationary Operational Environmental Satellites (GOES)

Built by Philco-Ford, the early GOES satellites were spin-stabilized (the spinning of the satellite kept it in a stable orientation with Earth), which meant they viewed the Earth only about ten percent of the time. NOAA operated these satellites from 1975 until 1994, when NOAA introduced a new generation of three-axis stabilized spacecraft labeled GOES I-M. GOES satellites, currently in operation, view the Earth 100 percent of the time and provide round-the-clock surveillance of the continental United States and coastal waters.

The United States operates two meteorological satellites in geostationary orbit about 22,300 miles above the Earth; one over the East Coast and one over the West Coast. NOAA’s National Environmental Satellite, Data and Information Service (NESDIS) operates the GOES series. New GOES satellites will be launched as required to keep the system operational. Space Systems/Loral (formerly Ford Aerospace) is the GOES I-M development contractor.

GOES satellites provide data for severe storm evaluation and information on cloud cover, winds, ocean currents, fog distribution, storm circulation and snow melt, using both visual and infrared imagery. They also receive transmissions from free-floating balloons, buoys and remote automatic data collection stations around the world. The imagery is also used to estimate rainfall during thunderstorms and hurricanes to help issue flash flood and flood warnings.

Because they are above a fixed point, the satellites provide a constant vigil for atmospheric triggers for severe weather conditions such as tornadoes, hail storms, hurricanes and flash floods. When these conditions develop, the satellites monitor storms and track their movements.

Polar Orbiting Satellites

NOAA weather and climate forecasters have a second set of space-based tools for monitoring severe weather and the atmosphere: the Polar Operational Environmental Satellite (POES). While GOES craft maintain a synchronous orbit to stay in one location above the Earth, POES craft circle the Earth in a sun-synchronous orbit (at an altitude of 450 nautical miles), in an almost north-south orbit, passing close to both poles. One POES crosses the equator in early morning and the other crosses in early afternoon. Operating as a team, these satellites ensure data for any region of the Earth are no more than six hours old.

POES spacecraft are used primarily for long-range weather and climate forecasting as well as search and rescue operations initiated by distress beacon signals. They also provide forecasters with information on cloud cover, storm location, temperature and heat balance in the Earth’s atmosphere.

Media contact:

Pat Slattery, NOAA National Weather Service: (816) 891-8914



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  Page last modified: 11-Mar-2010 9:35 AM