Sentinels in the Sky: Weather Satellites

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AUTHOR Haynes, Robert TITLE Sentinels in the Sky: Weather Satellites. INSTITUTION National Aeronautics and Space Administration, Washington, D.C.; National Oceanic and Atmospheric Administration (DOC), Rockville, Md. REPORT NO NASA- NF- l52(S) PUB DATE 89 NOTE 21p.; Colored pictures and drawings may not reproduce well. PUB TYPE Reports - Descriptive (141)

EDRS PRICE MFO1 /PCO1 Plus Postage. DESCRIPTORS Aerospace Technology; *Earth Science; *Meteorology; *Satellites (Aerospace); Science Materials; *Science Programs; Sciences; *Scientific Research; *Weather; Wind (Meteorology) IDENTIFIERS *National Aeronautics and Space Administration

ABSTRACT This publication describes forecasting weather activity using satellites. Information is included on the development of weather satellites, the National Oceanic and Atmospheric Administration (NOAA) Satellite System (including the polar-orbiting satellites), and the Geostationary Operational Environmental Satellite (GOES). The publication discusses the value of weather satellites; search and rescue; storm and rainfall forecasting; volcanic monitoring; fire detection; ocean temperature measurement; vegetation index mapping; and fish tracking. The instrumentation carried by weather satellites is discussed and definitions of the vocabulary used are lixted. (YP)

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4. Table of Contents

A View from Above r 3 Search and Rescue 4 Across Government Lines 7 'NOAA Satellite System 8 The' Value of Weather Satellites 8 Severe Storm Support 9 Rainfall 10 Volcanic Monitoring 10 Fire Detection 10 Oceanpgraphy 10 Vegetation Index Mapping 11 Fisheries 11 Polar-Orbiting Satellites 11 Instrumentation Carried by Weather Satellites 12 GOES Satellites 14 New Satellites, Sensors, Systems 15 Definitions 17

M r. 6

Sentinels in the Sky: Weather Sptellites

By Robert Haynes

This publication was develoOd as a joint effort between NASA and the National eanic and Atmospheric Admi ion (NOAA). Special thanks go.to Basil Littin, Public Affairs Officer, Ron Gird, Satellite Meteorologist, and James Sparkman, Physical Scientist, NOAA. 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 foil; v 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. .

TITLE PAGE: The current TIROS-N series of polar-orbiting satellites represent the fourth generation of these 'Sentinels in the Sky." TIROS stands for Television Infrared Observational Satellite.

2 A View From Above 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

Iy4 had little notion of large-scale weather behavior. If aerial views were made, they were taken from airplanes or weather )alloons but AL were of too short a duration to '41 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 firsi 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 systems as marked by the patterns of clouds, and provided meteorologists with a new toola nephanalysis, or cloud chart. These high-altitude views sharpened meteorologists' scrutiny of weather and of the environment, and promised even greater benefits to come. First television picture from space. On April 1, 1960, the TIROS-1 weather satellite sent this image. Since then, bigger and better Weather watchers along the tele- satellites have nwItiplied our graph lines had to base their under- knowledge about weather and its standing of the weather solely on behavior. what they could see from the ground.

3 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 radi- ometers to study Earth's heat distribution. Several satellites were placed in polar orbits rather -4t 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 allrwed 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 configura- Search and Rescue capsized boats, and persons in tions for the TIROS Operational other emergencies. Satellite (TOS) system. TOS The concept for a satellite-aided These signals are transmitted satellites were often called ESSA search and rescue project to special ground receiving sta- after the government agency that (SARSAT) began almost as soon tions in the United States and financed and operated them, the as the first satellites were placed overseas. The location of the sig- Environments 1 Sciences Services in Earth orbit. Experimental nal is computed and the nearest Administration. ESSA equipment had been placed on the rescue coordination center is no- (continued on page 6) early Nimbus satellites, and the tified. When an air or sea rescue first operational system was on team goes out, it has a "fix" with- TIROS. In 1976, the effort became in a few miles of the actual emer- an international project, with the gency. Satellite search has cut United States, Canada, and recovery time from days to a few France participating. hours. In 1980, the Soviet Union The program has been instru- agreed to equip COSMOS satel- mental not only in saving hun- lites with COSPAS repeaters. dreds of lives but also in saving Other nations have since joined millions of dollars in search in. The COSPAS/SARSAT satel- efforts. The system is proving lites monitor the entire surface of increasingly valuable as addi- the Earth, listenirg for distress tional enhancements and im- signals from downed airplanes, provements are made. Weather satellites are typically launched on unmanned rockets such as the Atlas and the Delta. Original- ly developed as weapon systems, these rockets have become the workhorses for launching civilian as well as military satellites.

4 Aviators and mariners in distress transmit an emergency signal to the COSPAS /SARSAT satellite. The sig- The ground receiving station pro- nal is received and retransmitted to cesses the signal and pinpoints the a ground receiving station, where a location. The location is given to the U.S. Coact Guard or Civil Air Patrol U.S. Mission Control Center, which rescue team is dispatched. alerts rescue teams in the area.

5 (continued from page 4) satellites were placed in Sun- synchronous orbits, so they would "Thanks to COSPAS/SARSAT pass over the same positions on the for saving us. Shortly after our Earth at the same time every day. rescue, the weather on the ice cap This would allow meteorologists to became rather poor and the view local cloud cover changes on winds were so high that several a 24-hour basis. days might have elapsed before With the success of TIROS, our rescue, had our position not NASA created a second-generation been pinpointed so accurately research satellite called Nimbus. by satellite," Dr. Justis reported. More complex than TIROS, Nim- They are pictured here, ELT bus satellites carried an APT sys- (emergency locater transmitter) tem, an advanced TV cloud- in hand, beside their new t mapping camera system, and an planethe damaged one was infrared radiometer that allowed abandoned on the ice cap. pictures at night for the first time. (Rescue June 1986) 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 Mount 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 east- wardly 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.

Four hours after crash-landing their position by COSPASI their twin-engined plane 9,300 SARSAT, the satellite search and feet above sea level on the Green-rescue system. Two hours later, land ice cap, Dr. R. Jeff Justis, a Danish helicopter picked Memphis surgeon, and his wife, them up. Sally, were spotted by a search plane that had been directed to

6 ci Satellites are the workhorses of a complete weather monitoring system. They scan the globe day Weather Monitoring System and night, transmitting back weather information such as temperatures, cloud formations, wind patterns, sea currents, etc. Wea,e Eid,loon For years, the swirling cloud Derived PrJffie patterns that weather satellites see Satpil Oedved P.nt have been standard props for TV Satellite weathercasters. Hardly anyone Instrumentation can tune in a weathercast without seeing a "satellite view

Radiosonde Across Government Lines 00 0 .32 .00 Temperatuf e rFaharenhe Our understanding of the weather has multiplied during the years weather satellites have operated The services 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 Weather Forecast appropriate orbits, the responsibility for operating them falls to another government agency; however, NASA continues its directs the nation's system of information is also shared by research role even after the space- weather satellites. NOAA man- government departments such as craft become operational. NASA's ages the processing and Agriculture, Interior, Defense, broad space program generates distribution of the millions of bits Transportation, and Energy. advanced technologies that are of data and images these satellites Weather satellites create an tested and applied to produce new produce daily. The prime international network. Informa- generations of satellites. consumer is NOAA's Weather tion is routinely shared among the The Department of Commerce's Service, which employs satellite member nations of the World National Oceanic and Atmo- data to create forecasts for Meteorological Organization as spheric Administration (NOAA) television, radio, and weather well as with nations that operate is the government agency that advisory services. Satellite their own weather satellites such as Japan, India, the Soviet weather satellite processing and from the Educational Programs Union, and members of the distribution facility is located in Officer. NASA Goddard Space European Space Agency. Suitland, Maryland, just outside Flight Center (202.3), Greenbelt, Washington, D.C. MD 20771.) Besides looking down on NOAA's operational weather weather conditions around the satellite system comprises two NOAA Satellite System world, satellites perform a host of types of satellites: Polar Orbiters other services. They assess crop and Geostationary Satellites NOAA was established in 1970 gr wth and other agricultural (GOES). The polar orbiters inside the U.S. Department of conditions, sense shifting ocean constantly circle the globe, Commerce with the mission to currents, and measure surface providing coverage of the globe ensure the safety of the general temperatures of oceans and land. every day. They circle in low public from atmospheric They relay data from surface orbits (850 km) and support large- phenomena and to provide the instruments that sense tide scale, multiday forecasts. The public with an understanding of conditions, Earth tremors, river GOES satellites circle in a much the Earth's environment and levels, and precipitation. higher orbit (35,000 km) so that resources. NOAA was also given Weather satellites also broad- their orbital rate exactly matches the responsibility to chart the cast the correct time as it is the rotation of the Earth's surface. airways, oceans, and waters of the precisely measured by the This keeps them above a fixed spot United States, and to guide the Department of Commerce's on the surface, providing a development of marine fisheries. National Bureau of Standards. constant vigil for severe weather One of the ways NOAA does this is They receive weather data from conditions that may spawn by operating its system of weather ocean buoys, weather balloons, and tornados, flash floods, hail storms, .satellites. Command and Data aircraft in flight, relaying this and hurricanes. Both kinds of Acquisition Stations in Wallops, data to the Data Acquisition satellites are necessary to provide a Virginia, and Fairbanks, Alaska, Stations. Using a facsimile complete global weather moni- send commands to the orbiting technique, they also broadcast toring system. satellites and receive data cloud cover pictures and charts. transmissions. A fully staffed (See "The Value of Weather Satellites.") The TIROS-N series of satellites The Value of Weather broadcast pictures and data so that Satellites any properly equipped receiving station on the ground can receive The value of weather satellites to the pictures without needing to link save lives has been known from the with an expensive computer. This beginning. Their ability to track capability has prompted many storms and permit early warnings schools across the country to install has been their greatest contribu- antennas and to build their own tion. However, their benefits do not weather receiving systems. end with observing the tops of (Secondary school teachers may clouds and storm systems. obtain a copy of Teacher's Guide Satellites can pinpoint different for Building and Operating temperature boundaries in ocean Weather Satellite Ground Stations surface areas, and give commer-

This view of the Western one is unique in that it shows two Hemisphere is a typical image hurricanes in the sante frame: one issued by the National Weather in the Gulf of Mexico and another Service operated by NOAA. This off the coast of California.

8 cial fishermen vital clues to the whereabouts of commercial fish :uch 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 seas,i on the Great Lakes into the winter months, generating extra economic activity for middle America and neighboring Canadian provinces.

Severe Storm Support 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 The benefits of weather satellites do not end with observing clouds. By Tornadoes are among the most vio- measuring the greenness of plant lent storms in nature. As yet, we chlorophyl, satellites can pinpoint still cannot predict when and where areas of drought, e.sert creep, or they will strike. But with the aid of deforestation. weather satellites we can delineate 'Most likely areas" and issue advisories to people who may be affected.

9 12 cycles, and track movements. federal and state agencies, and The valtYc of this information foreign countries is increasing steadily as new applications and small interactive computer systems are developed from the partnership of govern- Fire Detection ment, industry, and our high schools and universities. Blazes can be located by their smoke plumes and the heat regis- tered on infrared sensors. Sensors on both the polar orbiters and the Rainfall GOES have located wilderness fires in remote and difficult-to- Imagery from space is also used to Volcanic Monitoring reach areas, enabling emergency estimate rainfall during forces to better contain the flames. thunderstorms and hurricanes for Far above the surface, satellites flash flood warnings. Using GOES provide remarkable views of vol- satellite data, interactive computer canic eruptions. Both the polar or- technologies estimate the biting and GOES satellites monitor Oceanography precipitation amounts associated eruptions when they occur, allow- with severe weather. During ing scientists to analyze and track Large-scale weather patterns are Hurricane Diana, for example, dust clouds. affected by temperatures and cur- calculations indicated nearly 20 rents in the oceans. Polar-orbiting So far, numerous volcanic erup- sensors compute some 20-40 thou- inches of rainfall over North tions have been detected with sen- Carolina in a 2-day period. Actual sors on polar-orbiting satellites. sand global sea temperatures rainfall reached 18 inches. daily. In areas around the United The satellites and this data to the States, these readings reveal ocean Interactive computer technology is Smithsonian Sc'entific Event also used to estimate snowfall Alert Network where it is dissemi- cJr-ents and features such as the accumulations and overall extent nated to the scientific community, Gulf Stream, its wall and associat- of snow cover. Such data help ed eddies, upwellings off the West meteorologists issue winter storm Coast, and the Gulf of Mexico loop warnings and spring snow melt currents. advisories. Satellite sensors also Ocean surface temperatures help meteorologists study ocean in- detect ice fields, and map the 0"1";44 i movements of sea and lake ice. t 1 fluences on climate. Such an in- By also monitoring the southward fluence is El Nino, a widespread progression of freezing Seasonal 1 warming of the waters off the west temperatures, satellite imagery ti coast of South Americ a. In 1982-83, has often allowed forecasters El Nino and its associated weather- enough time to warn crop growers pattern reversal over the coast of to light smudge pots or take other South America brought severe measures to protect crops from flooding to Ecuad3r and northern damage. Peru, while it left a drought in other areas of the world

Top: Mount St. Helen's shown erupting May 18, 1980.

Using GOES Satellite data, IFFA Above: On April 6, 1986, a polar estimates the precipitation amounts orbiter took this picture of the associated with severe weather. Augustine Volcano in Alaska. Such imagery is useful in tracking the ash and dust clouds that spew from volcanic eruptions and in warning aircraft pilots. Vegetation Index Mapping Polar-Orbiting Satellites Since 1982, NOAA has used atellitPs 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 For normal weather coverage, some 16,000 global ieasure- help farmers monitor the growing NOAA operates two polar- ments daily to NOAA's Weather season. The multispectral images orbiting satellites. They circle Service computers, adding of the polar-orbiting satellites the globe in a north-south orbit, valuable information to make this possible passing over both the North and forecasting models, especially By measuring the greenness of South poles. One crosses the for remote ocean areas, where plant chlorophyl, scientists can equator in the morning and the convention& data are lacking. determine not only the health of other in the afternoon. They crops, but can also pinpoint areas of circle in a "Sun-synchronous" drought, desert creep, or deforesta- orbit of approximately 810850 tion the world over. Weather kilometers, and each obsevves scientists of many developing the entire Earth twice a day. NOAA Polar Orbiting nations have been trained in this Because they are Sun- Satellites technique under a program synchronous, these satellites conducted by NOAA for the Agency circle the Earth so that they cross for International Development. the equator at the same time Gilmore Creek, daily. The morning satellite Alaska crosses southward over the \Wallops equator at 7:30 am and the Island, Virginia Fisheries afternoon satellite crosses Stations northward at about 2:30 pm. 530 MI Commercial fishery operations Operating together as a pair, have also benefited from the data these satellites assure that Equator supplied by weather satellites. De- measurements for any regio-i of tc-mining the currents and sea the Earth are no more than six temperatures can help locate hours old. 28 8° suiools of tuna or salmon and can These polar orbiters provide Earth Rotation Orbit Path C. Per Orbit assist in tracking the movement of visible and infrared radiometer S fish eggs and larvae. Satellite data data that are used for imaging Orbit Plane can be used to study hypoxia, a se- purposes, radiation measure- Rotates Eastward vere lack of oxygen at deep sea lev- ments, and vertical temperature 1° Per Day els that can completely block the profiles, and can help calculate growth and development of .;ea life. water vapor content at several atmospheric levels. They send

Advanced TIROS-N (ATN) stations GOES satellites transmit" Instrumentation. stores measurements on tape, and their data to the National Weather later plays them back to NOAA's Carried By r. Service as well as directly to command and data acquisition amateur and professional users.' \stations. The satellites also Weather Future GOES satellites will broadcast in "real time" (this Satellites carry improved instruments for means transmissions are concurrent. imaging and simultaneous with the observation atmospheric sounding and provide of the instruments). These real- additional information on time broadcasts are available in atmospheric movements of water -Thoth high-resolution and low- vapor and the remapping of picture resolution picture images and can elements to permit.bette be received by anyone in the world calculation of winds based on equipped with a receiving station. cloud motion. Over the years, such receiving Both the polar-orbiting and GOES stations have been built and satellites carry instruments to Each polar-orbiting satellite, operated by foreign weather measure and monitor activities carries six primary systems. services, commercial American other than weather. For example, weather services, and high schools tbey monitor solar winds and Advanced Very High Resolution and colleges throughout the world. flares, and collect and relay data Radiometer. This instrument picked up by river and tide gages. senses clouds over both ocean and TIROS Operational Vertical seismometers, buoys, ships, land, using the visible and Sounder. This instrument airplanes, and' automatic weather infrared parts of the spectrum. It 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 pros ided system collect data from

ANL sensors placed on fixed and "Search and Rescue Satellite As- Australia There are over 1,000 moving platforms, including sisted Tracking", COSPAS is the knOwn WEFAX users who avail ships, buoys, d weather b'nlloons, Soviet equivalent. tleeiriselves of this free service.. and transmits clgtoa to a ground station antenna. Because ARGOS Earth Radiation Budget Experi- Space Environment Monitor. . also determinesie precise ment. This instrument is a radi-. This instrument is almost identi- location of thesenoving sensors, it ometer. It is designed to measure. cal to the sensors aboard the polar can serve w.ildlifimanagers by all radiation striking the Earth as orbiters. They measure the con- monitoring andrack4ng sensors well as all radiation leaving. . dition of the Earth's magnetic placed on birds and animals. Such monitoring enableA scientists field, the solar activity and radi- to measure the loss or gain of ter- ation around the spacecraft, and Space Err;zironment Monitor. This restrial energy to space.. Shifts in transmit these data to a central equipment measures energetic par- this energy "budgetaffect the . prOcessing facility. ticles emitted .by the Sun over es- Earth's average temperatutes, in sentiallythe full range of energies which even slight cHanges can The Data Collection System. and magnetic field variations in affect climatic. patterns. Similar to the Data Collection the Earth's near -space environ- and Platform Location System on ment-. Readings made by these in- GOES satellites carry four basic the polar orbiters, this system also struments are invaluable in meal sensor systems. gathers and relays readings uring the Sun's radiation activity. made by sensors placed on vari- Visible-Infrared Spin-Scan Radi- ous objects (both mobile and sta- Search and Rescue Tracking ometer and Atmospheric Sounder. tionary) at various locations. (COSPAS/SARSAT). This system This radiometer provides visible has already proven invaluable in infrared' and sounding measure- Search and Rescue Transponder. saving human life.Search and ments of the Earth. These images, This instrument is carried on rescue Iransmission equipment on together. with images received from GOES East, orbiting at 75" west board Weather satellites receives the polar-orbiting satellites, are longitude, and on GOES West, emergency signals from persons processed on the ground and then which is located at 135" west lon- in 'distress. The satellites transmit .radioed back up to the GOES for gitude. The GOES satellites can these signals to groundreceiving broadcast in graphic form as a relay distress signals at all stations in tl'w'lf.S. and overseas. "Weather Facsimile," .or WEFAX. times, but cannot locate them. SignalS are forwarded to.the near- WEFAX images are received by Only the low altitude polar- est rescue coordination center. ground stations on land as well as orbiting satellites can compute a These centers compute the location on ships. Currently, the GOES signal's location. The two satel- of the signals and give a rescue WEFAX transmissions are re- lites work together to create a team (usually.swithin a few miles) ceived from western Europe to east- search and rescue system, allow- the coordihates of the emergency ern Australia. ing a message to be intercepted by site. Both the U.S. and Soviet GOES satellites transmit their a GOES and relayed even though Union cooperate in.the Search and data to the National Weather Ser- a polar orbiter may be temporari- Rescue Tracking system: SAR- vice 'as well as to amateur and pro- ly outside radio "line of sight." SAT is the American acronym for fessional users as far away as (See "Search ka,c1 Rescue.") 410

13 GOES Satellites

The current Geostationary 1966 and followed it with another continuous monitoring Operational Environmental the next year. So far, NASA has necessary for intensive data Satellite (GOES) system consists placed eight of NOAA's GOES analysis and weather of GOES East and West, which satellites into orbit. Two of these, predictions. They look for such orbit at 75° west and 135° west GOES East and GOES West, are catastrophic events as longitude. Each views almost a fully operational. hurricanes, tornadoes, and other third of the Earth's surface: These GOES satellites severe storms and relay data to GOES East monitors North and complement the TIROS polar- ground receiving antennas. South America and most of the orbiting satellites. Both view These satellites duplicate some of Atlantic Ocean, while GOES remote areas and relay their data the functions on the polar- West looks down at North to instruments at NOAA's orbiting satellites, but from a America and the Pacific Ocean ground stations. distant broader perspective, they basin. The ;,wo operate together to By remaining stationed over add the advantage of main- send a full-face picture of the the same spot both day and night, taining a constant vigil. Earth every 30 minutes, day and the GOES can provide the kind of 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 a full-disc view of the Earth. NASA launched the first geostationary weather satellite in

Full-disk view from GOES East. Photo: Courier,ofTASCIVISI

Two GOES satellites observe the eastern and western U.S. and the adjacent ocean areas from a van- tage point over the equator. Photo: CourtesyofTASC/WSI

14 eagerly awaited instrument called New Satellites, Sensors, an Advanced Microwave Sounding Systems Unit For the first time, it will give forecasters global profiles of In the near future, satellite temperature and moisture inside research and applmatiuos will cloudy regions over Liie win id's resolve a global view of the oceans and continents The Current NOAA atmosphere, ocean, and land in instruments will provide new data GOES Satellite unprecedented breadth and depth every six hours, so that when the This will mean a big shift in satellite passes over an area of emphasis for the weather satellite severe storms, local forecasters system.Originally driven by will, for the first time, have space hardware, the system is information about atmospheric increasingly being driven by stability close to, and inside, a information. Data processing and storm system. This is important in 2,istribution will get more predicting storms because air mass emphasis as this information instability feeds tornadoes, explosion develops. hurricanes, and other severe Three new polar-orbiting weather conditions. satellites are to be launched Five new geostationary beginning in 1992, carrying a new, 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 ncn- 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 GOES Geostationery Orbit 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 operatir g. An unusual new sensor will constantly take pictures of the Sun, The next generation of GOES satellites will carry an unusual new sensor that will continuously watch the Sun. This will allow scientists to peer deep into the Sun's surface and study how flares and sunspots ar fect the weather on Earth.

15 L.) Space Station Polar Platform (No.v\c.,,Tt, 'HMS Antenna

ti\Iltlu tit I >volo;ible Solar P:inels

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detecting solar X-rays. This will meteorological platforms. These instruments will join the array of enable scientists to peer deeper into will function as part of NASA's existing sensors. Active the Sun's surface to spot energy Space Station. Whereas present instruments, such as radar, send flares that can affect Earth's weather satellites have life out a pulse or series of pulses to weather. expectancies of only a few year, "illuminate an area of interest." A Another new sensor will observe the repairable platforms are wind sensor using laser pulses is lightning flashes on Earth. By expected to last for many years. another potential gain for fore- counting these flashes, scientists NASA plans a serviceable casters. hope to learn more about how electri- geostationary platform for early in Already weather satellites cal exchange affects weather. the 21st century Discussion of a present an excellent example of For the period into the 21st centu- project to develop a microwave international cooperation in space. ry and beyond, plans are being sounder for geostationary flight is In the years ahead, many more drawn by NASA and NOAA for already in progress.Planners nations are expected to participate astronaut-tended, polar-orbiting anticipate that many "active" ia weather satellite programs.

16 *Definitions Radiometer-A satellite instru- Resolution-The value of a tele- El Nino -A warming of the surface ment that measures radiation photo lens is permitting the photog- waters of the eastern equatorial ( reflected sunlight and heat, or rapher to get a largerpicture of the Pacific that occurs at irregular in- thermal radiation). subject (sharper resolution) but less tervals of 2 to 7 years and lasts for of the surroundings. It's the same 1 to 2 years. The Southern Oscilla- Sounder-A special kind of radi- with satellites. Resolution of to- tion is a global-scale seesaw in at- ometer which measures changes of day's satellite "picture elements" mospheric pressure between Indo- atmospheric temperature with ("pixels") can vary from 10 meters nesia-North Australia, and the height, and changes in water va- (30 feet) for surveying uses to 1 km southeast Pacific. Together, they por content of the air at various (3000 feet) for weather satellites. are interacting parts of a single levels. global system of climate fluctua- WEFAX-Telegraphic abbrevia- tions popularly known as ENSO- Imager -A satellite instrument that tion for "weather facsimile," a The El Nino/Southern Oscillation, measures and maps sea-surfabe system for transmitting via radio so named because it first was asso- temperatures, cloudtop tempera- visual reproductions of weather ciated with Christmas, the time of tures, and land temperatures. Im- forecast maps, temperature sum- the Christ Child. ager data are converted by comput- maries, cloud analyses, etc. Most er into pictures. of these WEFAX transmissions Nephanalysis-Using cloud pic- are relayed by GOES spacecraft to- tures to study the relationship Infrared-Only a small part of the day. between cloud forms and storm electro-magnetic "spectrum" is centers. In classical mythology visible to us as light. The rest of it Platforms-Weathe satellites are Nephele was a woman Zeus formed can be sensed as heat, or infrared often called:space platforms" be- from a cloud. radiation. Infrared sensors serve cause theyrve rui emplacements as satellite "eyes" during periods in space or various instrument of darkness. syste The same term is applied to automatic weather data trans- Remapping-When the spherical mitters installed on buoys, bal- Earth is photographed by satellites, loons, ships, and planes, and areas lying near the outer edge of mounted in remote areas. Weath- the picture are distorted. Re. er satellites mapping is done to flatten the Earth feed into a standard projection.

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