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Weather Satellites Overview

S E N T I N E L S     I N     T H E     S K Y : W E A T H E R     S A T E L L I T E S

                            By Robert Haynes

When we talk about the weather, we often find ourselves fascinated
with its complexity and capriciousness. We are as curious as were our
ancient ancestors, who were acutely aware of how weather affected
their food supply and survival. Some tribes and cultures erected
permanent structures, with which they could continually chart the
course of the Sun and monitor seasonal changes.

Today we are no less relenting in our interest in the weather. We have
built and launched into space a family of weather satellites that
watch the weather from high above us. These "sentinels in the Sky" are
constantly on guard for those inevitable moments when friendly weather
turns to foe. They are tireless observers, telling us when a distant
low-pressure system over the Atlantic may develop into a hurricane and
threaten our lives with damaging winds. They monitor the warming ocean
currents of an El Nino that may affect crops in the United States or
Europe by changing expected precipitation patterns. They allow us to
understand the weather with some degree of certainty, and not be
victims of nature's whims.

Benjamin Franklin was the first American to suggest weather could be
predicted. From newspaper articles, Franklin deduced that severe
storms generally move across the nation from west to east. He further
deduced that if this were so, observers could follow a storm and
notify those ahead of its path that it was coming.

Franklin's ideas were finally put to practical use shortly after the
telegraph was invented in 1837. This revolutionary form of
communication soon spanned the country. It wasn't long until it was
used to link a network of weather watchers, who clicked their
observations along telegraph lines to a central office where a
national weather map was created.

Today, satellites are those observers, beeping messages to a receiving
antenna connected to a computer. Meteorologists analyze the messages
and use the data to predict how the weather will behave and how it
will affect us.

A     V I E W     F R O M     A B O V E

Weather watchers along the telegraph lines had to base their
understanding about the weather solely on what they could see from the
ground. Well into the 20th century, meteorologists still based most of
their knowledge on ground observations. Having no way to observe or
study weather patterns over long periods, and no way to monitor
cloudtops, meteorologists had little notion of large-scale weather
behavior. If aerial views were made, they were taken from airplanes or
weather balloons, but were of too short a duration to provide the kind
of information needed. Some progress was made in 1959 when the U.S.
Army Signal Corps launched VANGUARD II, but it was also short lived.

Then, in 1960, the National Aeronautics and Space Administration
(NASA) placed in orbit the first TIROS (Television Infrared
Observational Satellite). With its tiny TV cameras, TIROS flew over
more than two-thirds of the Earth's surface. Its pictures revealed
global weather patterns of clouds, and provided meteorologists with a
new tool--a nephanalysis, or cloud chart. These high-altitude views
sharpened meteorologists' scrutiny of weather and of the environment,
and promised even greater benefits to come.

NASA built and launched bigger and better TIROS satellites. By 1965
nine more TIROS satellites had been launched. They had progressively
longer operational times and carried infrared radiometers to study
Earth's heat distribution. Several satellites were placed in polar
orbits rather than near-equatorial ones so they could take pictures
over more of the Earth's surface.

TIROS 8 had the first Automatic Picture Transmission (APT) equipment.
This instrument allowed pictures to be sent back to Earth right after
they had been taken instead of stored for later transmission.
Eventually APT pictures could be received on fairly simple ground
stations.

TIROS 9 and 10 were test satellites of improved configurations for the
TIROS Operational Satellite (TOS) system. TOS satellites were often
called ESSA after the government agency that financed and operated
them, the Environmental Sciences Services Administration. ESSA
satellites were placed in Sun-synchronous orbits, so they would pass
over the same positions on the Earth at the same time every day. This
would allow meteorologists to view local cloud cover changes on a
24-hour basis.

With the success of TIROS, NASA created a second-generation research
satellite called NIBUS. More complex than TIROS, NIMBUS satellites
carried an APT system, an advanced TV cloud-mapping camera system, and
an infrared radiometer that allowed pictures at night for the first
time.

Seven NIMBUS satellites were placed in orbit between 1964 and 1978.
NIMBUS satellites tested space-borne meteorological equipment that led
to a fully operational weather observing service with 24-hour-a-day
coverage.

Today, weather satellites scan the Earth. With their vigilance, not a
single tropical storm anywhere on Earth goes undetected. The early
detection and warnings they provide have saved thousands of lives.

When Mt. St. Helens erupted on May 18, 1980, weather satellites looked
on as tons of volcanic ash were spewed into the atmosphere. They
photographed hourly the eastwardly spread of the massive dust clouds,
allowing meteorologists to warn aircraft pilots of the danger and to
study the effects such an explosion might have on the world's climate.
Fortunately, those effects in this instance were slight.

Satellites are the workhorses of a complete weather monitoring system.
They scan the globe day and night, transmitting back weather
information such as temperatures, cloud formations, wind patterns, sea
currents, etc. For years, the swirling cloud patterns have been
standard props for TV weathercasters. Hardly anyone can tune in a
weathercast without seeing a "satellite view."

A C R O S S     G O V E R N M E N T     L I N E S

Our understanding of the weather has multiplied during the years
weather satellites have operated. The service these weather watchers
provide span many governmental lines both here and overseas. NASA
contributes the research and development, and over sees procurement of
these spacecraft, and evaluates their performance in flight. Once NASA
launches the satellites into their appropriate orbits, the
responsibility for operating them falls to another government agency;
however, NASA continues its research role even after the spacecraft
become operational. NASA's broad space program generates advanced
technologies that are tested and applied to produce new generations of
satellites.

The Department of Commerce's National Oceanic and Atmospheric
Administration (NOAA) is the government agency that directs the
nation's system of weather satellites. NOAA manages the processing and
distribution of the millions of bits of data and images these
satellites produce daily. The prime consumer is NOAA's Weather
Service, which employs satellite data to create forecasts for
television, radio, and weather advisory services. Satellite
information is also shared by government departments such as
Agriculture, Interior, Defense, Transportation, and Energy.

Weather satellites create an international network. Information is
routinely shared among the member nations of the World Meteorological
Organization as well as with nations that operate their own weather
satellites such as Japan, India, the Soviet Union, and members of the
European Space Agency.

N O A A     S A T E L L I T E     S Y S T E M

NOAA was established in 1970 inside the U.S. Department of Commerce
with the mission to ensure the safety of the general public from
atmospheric phenomena and to provide the public with an understanding
of the Earth's environment and resources. NOAA was also given the
responsibility to chart the airways, oceans, and waters of the United
States, and to guide the development of marine fisheries. One of the
ways NOAA does this is by operating its system of weather satellites.
Command and Data Acquisition Stations in Wallops, VA and Fairbanks, AK
send commands to the orbiting satellites and receive data
transmissions. A fully staffed weather satellite processing and
distribution facility is located in Suitland, MD just outside
Washington DC.

Besides looking down on weather conditions around the world,
satellites perform a host of other services. They assess crop growth
and other agricultural conditions, sense shifting ocean currents, and
measure surface temperatures of oceans and land. They relay data from
surface instruments that sense tide conditions, Earth tremors, river
levels, and precipitation.

Weather satellites also broadcast the correct time as it is precisely
measured by the Department of Commerce's National Bureau of Standards.
They receive weather data from ocean buoys, weather balloons, and
aircraft in flight, relaying this data to the Data Acquisition
Stations. Using a facsimile technique, they also broadcast cloud cover
pictures and charts. [See "The Value of Weather Satellites"]

The TIROS-N series of satellites broadcast pictures and data so that
any properly equipped receiving station on the ground can receive the
pictures without needing to link with an expensive computer. This
capability has prompted many schools across the country to install
antennas and to build their own weather receiving systems. [Secondary
school teachers may obtain a copy of TEACHER'S GUIDE FOR BUILDING AND

OPERATING WEATHER SATELLITE GROUND STATIONS from the Educational
Programs Officer, NASA Goddard Space Flight Center, Greenbelt, MD
20771]

NOAA's operational weather satellite system comprises two types of
satellites: Polar Orbiters and Geostationary Satellites (GOES). The
polar orbiters constantly circle the globe, providing coverage of the
globe every day. They circle in low orbits (850 km) and support
large-scale, multiday forecasts. The GOES satellites circle in a much
higher orbit (35,000 km) so that their orbital rate exactly matches
the rotation of the Earth's surface. This keeps them above a fixed
spot on the surface, providing a constant vigil for severe weather
conditions that may spawn tornadoes, flash floods, hail storms, and
hurricanes. Both kinds of satellites are necessary to provide a
complete global weather monitoring system.

 T H E     V A L U E     O F     W E A T H E R     S A T E L L I T E S

The value of weather satellites to save lives has been known from the
beginning. Their ability to track storms and permit early warnings has
been their greatest contribution. However, their benefits do not end
with observing the tops of clouds and storm systems.

Satellites can pinpoint different temperature boundaries in ocean
surface areas, and give commercial fishermen vital clues to the
whereabouts of commercial fish such as tuna, herring and swordfish.
They can provide early frost warnings, which can save millions of
dollars a day for citrus growers who must then heat their groves. In
Hawaii, rain warnings are provided, giving crucial information for
sugarcane harvesting. Satellites also play a role in forest management
and fire control.

NOAA's polar-orbiting satellites observe snow and ice melting
conditions, enabling water supply managers to plan irrigation and
flood control. This is especially important to the multi-billion
dollar agricultural economies of our western states, where mountain
runoff provides an estimated 70 percent of the water supply. Satellite
ice monitoring helps extend the shipping season on the Great Lakes
into the winter months, generating extra economic activity for middle
America and neighboring Canadian provinces.

S E V E R E     S T O R M     S U P P O R T

Geostationary satellites continuously watch atmospheric conditions
that breed tornadoes, squall lines, and other severe storms. The
"triggers" for such events often can be detected by satellites before
the actual storms develop. When they do develop, the satellites
monitor storm life cycles, and track movements. The value of this
information is increasing steadily as new applications and small
interactive computer systems are developed from the partnership of
government, industry, and our high schools and universities.

R A I N F A L L

Imagery from space is also used to estimate rainfall during
thunderstorms and hurricanes for flash flood warnings. Using GEOS
satellite  data, interactive computer technologies estimate the
precipitation amounts associated with severe weather. During Hurricane
Diana, for example, calculations indicated nearly 20 inches of
rainfall over North Carolina in a 2-day period. Actual rainfall
reached 18 inches. Interactive computer technology is also used to
estimate 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. By also monitoring the southward
progression of freezing seasonal temperatures, satellite imagery has
often allowed forecasters enough time to warn crop growers to light
smudge pots or take other measures to protect crops from damage.

V O L C A N I C     M O N I T O R I N G

Far above the surface, satellites provide remarkable views of volcanic
eruptions. Both the polar orbiting and GOES satellites monitor
eruptions when they occur, allowing scientists to analyze and track
dust clouds.

So far, numerous volcanic eruptions have been detected with sensors on
polar-orbiting satellites. The satellites send this data to the
Smithsonian Scientific Event Alert Network where it is disseminated to
the scientific community, federal and state agencies, and foreign
countries.

F I R E     D E T E C T I O N

Blazes can be located by their smoke plumes and the heat registered on
infrared sensors. Sensors on both the polar orbiters and the GOES have
located wilderness fires in remote and difficult-to-reach areas,
enabling emergency forces to better contain the flames.

O C E A N O G R A P H Y

Large-scale weather patterns are affected by temperatures and currents
in the oceans. Polar-orbiting sensors compute some 20-40 thousand
global sea temperatures daily.  In areas around the United States,
these readings reveal ocean currents and features such as the Gulf
Stream, its wall and associated eddies, upwellings off the West Coast,
and the Gulf of Mexico loop currents.

Ocean surface temperatures help meteorologists study ocean influences
on climate. Such an influence is El Nino, a widespread warming of the
waters off the west coast of South America. In 1982-83, El Nino and
its associated weather-pattern reversal over the coast of South
America brought severe flooding to Ecuador and northern Peru, while it
left a drought in other areas of the world.

V E G E T A T I O N     I N D E X     M A P P I N G

Since 1982, NOAA has used satellites to look at the progress of crops
and to study vegetation growth. Since 1984, vegetation index maps have
been sent to the Weather Service field offices to help farmers monitor
the growing season. The multispectral images of the polar-orbiting
satellites make this possible.

By measuring the greenness of plant chlorophyl, scientists can
determine not only the health of crops, but can also pinpoint areas of
drought, desert creep, or deforestation the world over. Weather
scientists of many developing nations have been trained in this
technique under a program conducted by NOAA for the Agency for
International Development.

F I S H E R I E S

Commercial fishery operations have also benefited from the data
supplied by weather satellites. Determining the currents and sea
temperatures can help locate schools of tuna or salmon and can assist
in tracking the movement of fish eggs and larvae. Satellite data can
be used to study hypoxia, a severe lack of oxygen at deep sea levels
that can completely block the growth and development of sea life.

N E W     S A T E L L I T E S ,     S E N S O R S ,     S Y S T E M S

In the near future, satellite research and applications will resolve a
global view of the atmosphere, ocean and land in unprecedented breadth
and depth. This will mean a big shift in emphasis for the weather
satellite system. Originally driven by space hardware, the system is
increasingly being driven by information. Data processing and
distribution will get more emphasis as this information explosion
develops.

Three new polar-orbiting satellites are to be launched beginning in
1992, carrying a new, eagerly awaited instrument called an Advanced
Microwave Sounding Unit. For the first time, it will give forecasters
global profiles of temperature and moisture inside cloudy regions over
the world's oceans and continents. The instruments will provide new
data every six hours, so that when the satellite passes over an area
of severe storms, local forecasters will, for the first time, have
information about atmospheric stability close to, and inside, a storm
system. This is important in predicting storms because air mass
instability feeds tornadoes, hurricanes, and other severe weather
conditions.

Five new geostationary satellites of an entirely new design, carrying
improved instruments, are to appear at intervals beginning in 1989.
For two generations all the GOES spacecraft have been spinning like
tops as they move along their orbits. The new GOES will be
non-spinning and their instruments will be able to view the Earth
continuously, rather than "eyeing" a scene once with each revolution.
Both the satellite and its solar photovoltaic-panel powerplant will be
larger.

This new design is expected to improve dramatically the performance of
both imagers and sounders. When this new satellite appears it will no
longer be necessary to turn off a sounder while an imager is
operating. An unusual new sensor will constantly take pictures of the
Sun, detecting solar X-rays. This will enable scientists to peer
deeper into the Sun's surface to spot energy flares that can affect
Earth's weather.

Another new sensor will observe lightning flashes on Earth. By
counting these flashes, scientists hope to learn more about how
electrical exchange affects weather.

For the period into the 21st century and beyond, plans are being drawn
by NASA and NOAA for astronaut-tended, polar-orbiting meteorological
platforms. These will function as part of NASA's Space Station.
Whereas present weather satellites have life expectancies of only a
few years, the repairable platforms are expected to last for many
years.

NASA plans a serviceable geostationary platform for early in the 21st
century. Discussion of a project to develop a microwave sounder for
geostationary flight is already in progress. Planners anticipate that
many "active" instruments will join the array of existing sensors.
Active instruments, such as radar, send out a pulse or series of
pulses to "illuminate an area of interest." A wind sensor using laser
pulses is another potential gain for forecasters.

Already weather satellites present an excellent example of
international cooperation in space. In the years ahead, many more
nations are expected to participate in weather satellite programs.

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I N S T R U M E N T A T I O N C A R R I E D     B Y W E A T H E R     S A T E L L I T E S


Both the polar-orbiting and GOES satellites carry instruments to
measure and monitor activities other than weather. For example, they
monitor solar winds and flares, and collect and relay data picked up
by river and tide gages, seismometers, buoys, ships, airplanes, and
automatic weather stations. GOES satellites transmit their data to the
National Weather Service as well as directly to amateur and
professional users.

Future GOES satellites will carry improved instruments for concurrent
imaging and atmospheric sounding and provide additional information on
atmospheric movements of water vapor and the remapping of picture
elements to permit better calculation of winds based on cloud motion.

EACH POLAR-ORBITING SATELLITE CARRIES SIX PRIMARY SYSTEMS.

ADVANCED VERY HIGH RESOLUTION RADIOMETER. This instrument senses
clouds over both ocean and land, using the visible and infrared parts
of the spectrum. It stores measurements on tape, and later plays them
back to NOAA's command and data acquisition stations. The satellites
also broadcast in "real time" (this means transmissions are
simultaneous with the observations of the instruments). These
real-time broadcasts are available in both high-resolution and
low-resolution picture images and can be received by anyone in the
world equipped with a receiving station. Over the years, such
receiving stations have been built and operated by foreign weather
services, commercial American weather services, and high schools and
colleges throughout the world.

TIROS OPERATIONAL VERTICAL SOUNDER. This instrument combines data from
three complementary instrument units to provide temperature and
moisture data from the Earth's surface up through the atmosphere.

ARGOS DATA COLLECTION AND PLATFORM LOCATION SYSTEM. The instruments in
this French-provided system collect data from sensors placed on fixed
and moving platforms, including ships, buoys, and weather balloons,
and transmits data to a ground station antenna. Because ARGOS also
determines the precise location of these moving sensors, it can serve
wildlife managers by monitoring and tracking sensors placed on birds
and animals.

SPACE ENVIRONMENT MONITOR. This equipment measures energetic particles
emitted by the Sun over essentially the full range of energies and
magnetic field variations in the Earth's near-space environment.
Readings made by these instruments are invaluable in measuring the
Sun's radiation activity.

SEARCH AND RESCUE TRACKING (COSPAS/SARSAT). This system has already
proven invaluable in saving human life. Search and rescue transmission
equipment on board weather satellites receives emergency signals from
persons in distress. The satellites transmit these signals to ground
receiving stations in the U.S. and overseas. Signals are forwarded to
the nearest rescue coordination center. These centers compute the
location of the signals and give a rescue team (usually within a few
miles) the coordinates of the emergency site. Both the U.S. and Soviet
Union cooperate in the Search and Rescue Tracking system: SARSAT is
the American acronym for "Search and Rescue Satellite Assisted
Tracking"; COSPAS is the Soviet equivalent.

EARTH RADIATION BUDGET EXPERIMENT. This instrument is a radiometer. It
is designed to measure all radiation striking the Earth as well as all
radiation leaving . Such monitoring enables scientists to measure the
loss or gain of terrestrial energy to space. Shifts in this energy
"budget" affect the Earth's average temperatures, in which even slight
changes can affect climatic patterns.

GEOS SATELLITES CARRY FOUR BASIC SENSOR SYSTEMS.

VISIBLE-INFRARED SPIN-SCAN RADIOMETER AND ATMOSPHERIC SOUNDER. This
radiometer provides visible infrared and sounding measurements of the
Earth. These images, together with images received from the
polar-orbiting satellites, are processed on the ground and then
radioed back up to the GOES for broadcast in graphic form as a
"Weather Facsimile," or WEFAX. WEFAX images are received by ground
stations on land as well as on ships. Currently, the GOES WEFAX
transmissions are received from western Europe to eastern Australia.

GOES satellites transmit their data to the National Weather Service as
well as to the amateur and professional users as far away as
Australia. There are over 1,000 known WEFAX users who avail themselves
to this free service.

SPACE ENVIRONMENT MONITOR. This instrument is almost identical to the
sensors aboard the polar orbiters. They measure the condition of the
Earth's magnetic field, the solar activity and radiation around the
spacecraft, and transmit these data to a central processing facility.

THE DATA COLLECTION SYSTEM. Similar to the Data Collection and
Platform Location System on the polar orbiters, this system also
gathers and relays readings made by sensors placed on various objects
(both mobile and stationary) at various locations.

SEARCH AND RESCUE TRANSPONDERS. This instrument is carried on GOES
East, orbiting at 75 degrees west longitude, and on GOES West, which
is located at 135 degrees west longitude. The GOES satellites can
relay distress signals at all times, but cannot locate them. Only the
low altitude polar-orbiting satellites can compute a signal's
location. The two satellites work together to create a search and
rescue system, allowing a message to be intercepted by a GOES and
relayed even though a polar orbiter may be temporarily outside radio
"line of sight." [See "Search and Rescue"]

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S E A R C H     A N D     R E S C U E

The concept for a satellite-aided search and rescue project (SARSAT)
began almost as soon as the first satellites were placed in Earth
orbit. Experimental equipment had been placed on the early Nibus
satellites, and the first operational system was on TIROS. In 1976,
the effort became an international project, with the United States,
Canada, and France participating.

In 1980, the Soviet Union agreed to equip COSMOS satellites with
COSPAS repeaters. Other nations have since joined in. The
COSPAS/SARSAT satellites monitor the entire surface of the Earth,
listening for distress signals from downed airplanes, capsized boats,
and persons in other emergencies.

These signals are transmitted to special ground receiving stations in
the United States and overseas. The location of the signal is computed
and the nearest rescue coordination center is notified. When an air or
sea rescue team goes out, it has a "fix" within a few miles of the
actual emergency. Satellite search has cut recovery time from days to
a few hours.

The program has been instrumental not only in saving hundreds of lives
but also in saving millions of dollars in search efforts. The system
is proving increasingly valuable as additional enhancements and
improvements are made.

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P O L A R  -  O R B I T I N G     S A T E L L I T E S

For normal weather coverage, NOAA operates two polar-orbiting
satellites. They circle the globe in a north-south orbit, passing over
both the North and South poles. One crosses the equator in the morning
and the other in the afternoon. They circle in a "Sun-synchronous"
orbit of approximately 810 - 850 kilometers, and each observes the
entire Earth twice a day. Because they are Sun-synchronous, these
satellites circle the Earth so that they cross the equator at the same
time daily. The morning satellite crosses southward over the equator
at 7:30 am and the afternoon satellite crosses northward at about 2:30
pm. Operating together as a pair, these satellites assure that
measurements for any region of the Earth are no more than six hours
old.

These polar orbiters provide visible and infrared radiometer data that
are used for imaging purposes, radiation measurements, and vertical
temperature profiles, and can help calculate water vapor content at
several atmospheric levels. They send some 16,000 global measurements
daily to NOAA's Weather Service computers, adding valuable information
to forecasting models, especially for remote ocean areas, where
conventional data are lacking.

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G O E S     S A T E L L I T E S

The current Geostationary Operational Environmental Satellite (GOES)
system consists of GOES East and West, which orbit at 75 degrees west
and 135 degrees west longitude. Each views almost a third of the
Earth's surface: GOES East monitors North and South America and most
of the Atlantic Ocean, while GOES West looks down at North America and
the Pacific Ocean basin. The two operate together to send a full-face
picture of the Earth every 30 minutes, day and night. Pictures of
smaller areas can be sent more often should a storm need monitoring.
These satellites give meteorologists nearly continuous viewing of
storms and cloud patterns, as well as measurements of wind fields at
cloud altitudes.

The GOES satellites circle the Earth in a "geosynchronous" orbit. This
means they orbit the equatorial plane of the Earth at a speed and
altitude that allows them to hover continuously over one position on
the surface. The geosynchronous plane is about 35,800 kilometers above
the Earth, high enough to allow satellites orbiting there to have a
full-disc view of the Earth.

NASA launched the first geostationary weather satellite in 1966 and
followed it with another the next year. So far, NASA has placed eight
of NOAA's GOES satellites into orbit. Two of these, GOES East and GOES
West, are fully operational.

These GOES satellites complement the TIROS polar-orbiting satellites.
Both view remote areas and relay their data to instruments at NOAA's
ground stations.

By remaining stationed over the same spot both day and night, the GOES
can provide the kind of continuous monitoring necessary for intensive
data analysis and weather predictions. They look for such catastrophic
events as hurricanes, tornadoes, and other severe storms and relay
data to ground receiving antennas. These satellites duplicate some of
the functions on the polar-orbiting satellites, but from a distant
broader perspective, they add the advantage of maintaining a constant
vigil.

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D E F I N I T I O N S

RADIOMETER - A satellite instrument that measures radiation (reflected
             sunlight and heat, or thermal radiation).

SOUNDER    - A special kind of radiometer which measures changes of
             atmospheric temperature with height, and changes in water
             vapor content of the air at various levels.

IMAGER     - A satellite instrument that measures and maps sea-surface
             temperatures, cloudtop temperatures, and land
             temperatures. Imager data are converted by computer into
             pictures.

INFRARED-ONLY
            - A small part of the electro-magnetic "spectrum" is
              visible to us as light. The rest of it can be sensed as
              heat, or infrared radiation. Infrared sensors serve as
              satellite "eyes" during periods of darkness.

REMAPPING   - When the spherical Earth is photographed by satellites,
              areas lying near the outer edge of the picture are
              distorted. Remapping is done to flatten the Earth into a
              standard projection.

RESOLUTION - The value of a telephoto lens is permitting the
             photographer to get a larger picture of the subject
             (sharper resolution) but less of the surroundings. It's
             the same with satellites. Resolution of today's satellite
             "picture elements" ("pixels") can vary from 10 meters (30
             feet) for surveying uses to 1 km (3000 feet) for weather
             satellites.

WEFAX      - Telegraphic abbreviation for "weather facsimile," a
             system for transmitting via radio visual reproductions of
             weather forecast maps, temperature summaries, clouds
             analyses, etc. Most of these WEFAX transmissions are
             relayed by GOES spacecraft today.

PLATFORMS   - Weather satellites are often called "space platforms"
              because they serve as emplacements in space for various
              instrument systems. The same term is applied to
              automatic weather data transmitters installed on buoys,
              balloons, ships, and planes, and mounted in remote
              areas. Weather satellites collect this data and feed it
              into the daily world weather analysis.

EL NINO   -   A warming of the surface waters of the eastern
              equatorial Pacific that occurs at irregular intervals of
              2 to 7 years and lasts for 1 to 2 years. The SOUTHERN
              OSCILLATION is a global-scale seesaw in atmospheric
              pressure between Indonesia-North Australia, and the
              southeast Pacific. Together, they are interacting parts
              of a single global system of climate fluctuations
              popularly known as ENSO--The El Nino/Southern
              Oscillation, so named because it first was associated
              with Christmas, the time of the Christ Child.

NEPHANALYSIS
            - Using cloud pictures to study the relationship between
              cloud forms and storm centers. In classical mythology
              Nephele was a woman Zeus formed from a cloud.

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NASA FACTS, SENTINELS IN THE SKY: WEATHER SATELLITES, Haynes, NF-152,
NASA/NOAA

Comments and questions: Jennifer Green
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mental Satellite (GOES) system consists of GOES East and West, which orbit at 75 degrees west and 135 degrees west longitude. Each views almost a third of the Earth's surface: MGkm!#g3v4| R&hU O  6 8   F H  [ ( p ?|LL_Q.r?f!aAbd5{GQ@Ofsu=|8v@ !!\!!!("o"""D####$$O$$$#%i%%%%&Y&&&'!'g'''5(|((()J)R)T)))$*e*!ce***5+y++++,-,u,w,,-L----.M.../b/u/w///;000 1S11111172~223D3333334[444$5e55576667K777778B88888 9h999999":j::::;;J;;;<]<<<<=Y===>>F>H>!cH>>>?c???? @N@@@@@AACAAABXBBBBB.CvCCC>DDDDDE_EEE2FvFFFAGNGPGGG!H]HHH/I8I:IIIJNJJJJJ)KjKKKK LaLLLLL:MMM NLNNNNOGOOOOO2P4P6PxPPQIQQQQQ!aQ,RtRRRSSSSTTTTTUTUUUV=V?VVV W WUWWW%XlXXXX YNYYYYY6Z~ZZ [R[[[#\h\\\\]g]]]:^a^c^^^^#_`___%`f````4a|aaaa"bgbbbb2cycccc9d|ddeEeeeeeCfEflfnfffcf9g~gggg*hehhhii[iii/jvjjjjkUkmkokkkkk1lyllmImmmnbnnnnn7o|oopPppppppq qfqqq5r}rrsMsssss2tuttuHufuhuuuyUyWyyyyzfzzczzz&{m{{{{{|e||||,}t}}}}~`~~~7QS cڀ!`0fh3vA~ÄV؅څ"$k|φ.9:IKMDF  ͅ ,@"-8CNNP.\ogjr|(}ͅ EB?BGBD  # H  H  MDe*H>QfzMEFGHIJK(Times New Roman Symbol&Arial"h腌 &5Jennifer L. GreenJennifer L. Green