NOAA TECHNOLOGY TAKES WEATHER DETECTION TO NEW HEIGHTS SINCE PALM SUNDAY TORNADO OUTBREAK
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
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.
Pat Slattery, NOAA National Weather Service: (816) 891-8914