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2 Earth Observations from Space: The Early History âSpace technology affords new opportunities for scientific In 1955 the United States announced it would launch a observation and experiment, which will add to our scientific Earth satellite during the International ÂGeophysical knowledge and understanding of the earth.â Year (IGY) of 1957-1958. Sputnik, however, diverted the âPresidentâs Science Advisory Committee (1958) worldâs attention from scientific concerns and focused American perceptions on a âmissile gapâ and possible The space age officially began on October 4, 1957, with national security threats from space. The November launch the dramatic and historic launch of Sputnik 1 by the Soviet of Sputnik 2 further fueled these fears. In response, and with Union, but there are much deeper roots. Robert H. Goddard the Navyâs Vanguard Program languishing, the U.S. Depart- developed liquid-fueled rockets and used them for weather ment of Defense used a modified Redstone military missile, photography in the 1920s; remote sensing radio technology the Juno 1, to launch the first U.S. satellite, Explorer 1, on was developed in the 1930s and 1940s; a V-2 rocket flight in January 31, 1958. 1947 photographed clouds from an altitude of 100 miles; and That year Congress enacted the National Defense by 1954 instrumented sounding rockets had serendipitously Education Act, which provided dramatically increased photographed an unknown tropical storm (Figure 2.1). support for both basic research and science education at all levels and benefited the nation in subsequent genera- tions in ways that could not have been foreseen at the time. The National Aeronautics and Space Act created a new agencyâthe National Aeronautics and Space Administration (NASA)âto consolidate and lead the U.S. space effort. Its mission included expanding knowledge of phenomena both within the atmosphere and in outer space and developing and operating vehicles capable of carrying instruments for peaceful and scientific purposes in cooperation with other nations. Also in 1958, the Presidentâs Science Advisory Committee pointed out that a satellite in orbit could be used for three sci- entific purposes: â(1) it can sample the strange new environment though which it moves; (2) it can look down FIGURE 2.1â Image of a previously undetected tropical storm in the Gulf of Mexico and see the earth as it has never been photographed by an Aerobee sounding rocket in 1954. SOURCE: Hubert and Berg (1955). seen before; and (3) it can look out Reprinted with permission from the American Meteorological Society, copyright 1955. into the universe and record informa- 10
EARTH OBSERVATIONS FROM SPACE: THE EARLY HISTORY 11 tion that can never reach the earthâs surface because of the intervening atmosphereâ (PSAC 1958). BOX 2.1 Even in 1958, scientists knew that Earth-orbiting satel- James A. Van Allen (1914-2006) lites would encounter and be able to measure the charged plasma of the solar wind, the three-dimensional structure of James A. Van Allen (Figure 2.2) was born in Mount Earthâs gravitational and magnetic fields, and other energy Pleasant, Iowa; he earned a Ph.D. in physics from fluxes and fast-moving particles in near space. Satellites the University of Iowa and spent almost his entire could detect incoming cosmic rays and be used to test career there in the Department of Physics and As- Einsteinâs general theory of relativity; they could measure tronomy. During World War II he served in the Navy, solar energy at the top of the atmosphere to determine how working at the Carnegie Institution of Washington much is reflected and radiated back to space by clouds, and the Johns Hopkins University Applied Physics oceans, continents, and ice sheets; and they could look Laboratory, where he helped develop and test the down at Earth to expand surveillance of weather systems radio proximity fuse. After the war he developed from about 10 percent to practically 100 percent of Earthâs instrument packages for Â upper-atmosphere and surface. The scientific accomplishments of five prominent near-space scientific exploration and was head of early satellites (Explorer 1, Explorer 7, TIROS 1 [Televi- development for the Aerobee sounding rocket. sion Infrared Observing Satellite], ATS 1 [Application In 1950, Van Allen hosted a dinner at his home TechÂnology Satellite], and the Nimbus series), all launched where plans were initiated for the IGYâa coordinat- in the first two decades of the space age, fulfilled many of ed, international, and comprehensive study of Earth these expectations. conducted in 1957-1958. Two of the most prominent achievements of the IGY were the discovery of the Van Allen radiation belts and a new, pear-shaped EARLY SATELLITES AND PIONEERS model of Earth. Van Allen subsequently served as âAt the dawn of the Space Age, the nature of space principal investigator for more than 25 space sci- exploration was already apparent: It always leads to unex- ence missions. He was active in NASA, National pected discoveries about our universe and the processes Academy of Sciences, and American Geophysical Union affairs and was an articulate and outÂspoken that shape our environmentâ (Friedman 2006). On May 1, advocate of small, inexpensive space missions. 1958, University of Iowa scientist James Van Allen (Box 2.1, Figure 2.2) announced that Geiger-MÃ¼ller counters aboard the Jet Propulsion Laboratory (JPL) Explorer 1 (Figure 2.3) and Explorer 3 satellites had been swamped by high radiation levels at certain points in their orbits, indicating that powerful radiation belts, later known as the Van Allen belts, surround Earth (Van Allen et al. 1958, Van Allen and Frank 1959). Vanguard 1, the fourth artificial satellite launched, provided important geodetic information about the shape of the Earth, specifically its north-south asymmetry (OâKeefe et al. 1960). NASA launched the worldâs first weather satellite, TIROS 1, on April 1, 1960 (Figure 2.4). TIROS 1 flew in a nearly circular, prograde orbit of 48 degrees inclination. It took television (Figure 2.5) and (on later flights) infrared photos of weather patterns from space, serving as a âstorm patrolâ for early warnings, an aid to weather analysis and forecasting, and a research tool for atmospheric scientists (Wexler and Caskey 1963). The images revealed surprising new cloud features: ocean storms, including the spiral band structure of hurricanes and an unreported typhoon near New Zealand; the unexpectedly great extent and structure of mountain wave clouds over South America; and rapid FIGURE 2.2â James A. Van Allen, in his office changes occurring during cyclogenesis. In a posthumous on the Â University of Iowa campus in Iowa City, article published in 1965, Harry Wexler (Box 2.2, FigureÂ 2.6) 1990. SOURCE: Photo by Tom Jorgensen, Univer- sity of Iowa. Reprinted with permission from Tom wrote, âThe TIROS satellites disclosed the existence of J Â orgensen, University of Iowa. storms in areas where few or no observations previously existed, revealed unsuspected structures of storms even in
12 EARTH OBSERVATIONS FROM SPACE: THE FIRST 50 YEARS OF SCIENTIFIC ACHIEVEMENTS FIGURE 2.5â TIROS 1: first TV picture of weather from space, April 1, 1960. SOURCE: NASA. FIGURE 2.3â Explorer 1 with architects (left to right) William H. Pickering, director of the Jet Propulsion Laboratory; James A. Van Allen, chief scientist; and Wernher von Braun, leader of the Armyâs Redstone Arsenal team. SOURCE: Jet Propulsion Laboratory. areas of extensive observational coverage, depicted snow fields over land, ice floes over water, and temperature pat- terns on land and ocean as well as temperatures of tops of cloud layers.â Because its accomplishments were clearly accessible to the general public, the TIROS program enjoyed strong politi- cal support. The series of 10 TIROS satellites proved to be reliable and operationally successful, providing proof of the concept that sustained weather observations from space were possible. In 1966 this was continued as the Environmental Science Services Administration series, the Improved TIROS Operational System, TIROS M, TIROS N, and the National Oceanic and Atmospheric Administration (NOAA) series of satellites. Launched by NASA on October 13, 1959, ExplorerÂ 7 carried a number of instruments including solar X-ray, Lyman-alpha, cosmic radiation, and micrometeor Âdetectors. Significantly, it also carried University of Wisconsin, M Â adison scientist Verner Suomiâs (Box 2.3, Figure 2.8) improved radiometer, which took the first Earth radiation measurements from space and initiated the era of satel- lite studies of climate. These observations established that Earthâs energy budget varies markedly due to the effect of clouds and other absorbing constituents (Suomi 1961). Beginning in 1963, in collaboration with Robert Parent, FIGURE 2.4â TIROS 1 and technician. SOURCE: National Ar- chives Photo 370-MSP-4-147. Suomi developed a spin-stabilized camera that continuously
EARTH OBSERVATIONS FROM SPACE: THE EARLY HISTORY 13 monitored the weather and its motions over a large fraction of Earthâs surface. Their âspin-scan cameraâ first flew on BOX 2.2 NASAâs ATS 1, a spin-Âstabilized communications satellite Harry Wexler (1911-1962) launched into geoÂstationary orbit in December 1966 (Suomi et al. 1971). Harry Wexler (Figure 2.6) was born in Fall River, Suomiâs âgadget,â as he called all his inventions, pro- Massachusetts, and earned a Ph.D. in meteorology duced spectacular full-disk images of Earth. It allowed sci- from the Massachusetts Institute of Technology entists to observe weather systems as they developed, instead under C. G. Rossby. He spent most of his career of glimpsing small bits at odd intervals, and it provided the with the U.S. Weather Bureau and also served first full-Earth disk: high-quality, cloud-cover pictures taken as an instructor of military weather cadets during from a geostationary satellite. The image had a resolution of World War II. As head of research for the Weather about 3 km and allowed meteorologists to identify and study Bureau, Wexler participated in the development of significant cloud patterns, including those in the tropics, a number of new technologies, including airborne their change with time, the structure of storms, and the way observations, sounding rockets, radar, the use of synoptic-scale weather interacted with local phenomena. electronic computers for numerical weather predic- The spin-scan system, used in conjunction with ground and tion and general circulation studies, and satellite tropospheric balloon observations, also contributed to quan- meteorology. He also served as chief scientist for titative measurements of the dynamics of air motion, cloud the U.S. expedition to the Antarctic for the IGY and heights, and the amount of atmospheric pollution. Using established a number of atmospheric baseline mea- the communications capabilities of ATS 1, NASA was able surements of trace gases, including carbon dioxide to send cloud images and weather data to ground stations and ozone. From the early 1950s, Wexler promoted in the United States, Canada, Japan, Australia, and islands the use of satellites in meteorology. Wexler, who in the Pacific. The weather satellite images seen today on played a central role in the development of Explorer worldwide television and the Internet are direct descendents and TIROS, foresaw that information gathered from of Suomiâs invention. They are essential for warning the satellites would be of great value for severe weather public of tropical storm landfalls and other potential natural warnings, measurement of Earthâs heat budget, disasters. and detection of environmental changes, both im- A color version of the spin-scan camera flew on ATS 3 mediate and long term. Always interested in global in 1967. It was used to detect the genesis of severe storms studies of weather and climate, Wexler was an in the American Midwest, document the complete life cycle enthusiastic promoter of the World Weather Watch, of hurricanes, and support the Barbados Oceanographic which became a reality in 1963, shortly after his and Meteorological Experiment (BOMEX) study of energy death. exchanges between the ocean and the atmosphere. Sub- sequent experiments involved a Visible and Infrared Spin Scan Radiometer (VISSR) on Synchronous Meteorological Satellites (SMS) 1 and 2, launched in 1974 and 1975, and the 13Â Geostationary Operational Environmental Satellites (GOES) launched since 1975. These experiments enabled Suomi and his team to document that Earth absorbed more of the Sunâs energy than originally thought and to demonstrate that it was possible to measure and quantify seasonal changes in the global heat budget. One of Suomiâs important contributions to satellite data processing was the Man-Computer Interactive Data Access System, developed by an interdisciplinary team of electronics and computer engineers and programmers at the Space Science and Engineering Center at the University of Wisconsin, Madison. This data system provided an important interface between the user, the computer, the databases, and ultimately, real-time sensors, including satellite-based instru- ments, ground-based radar, and conventional and automated FIGURE 2.6â Harry Wexler. SOURCE: Wexler and J. E. Caskey, Jr. (1963). North-Holland Publishing Co., meteorological stations (Chatters and Suomi 1975). It was A Â msterdam, 1963. used for both research and operational purposes in support of data collected during the Global Atmospheric Research Program (GARP) Atlantic Tropical Experiment in 1974 and
14 EARTH OBSERVATIONS FROM SPACE: THE FIRST 50 YEARS OF SCIENTIFIC ACHIEVEMENTS the First GARP Global Experiment, subsequently known as and clearly revealed the outlines of major ocean currents. the Global Weather Experiment (GWE), 1977-1979. NimbusÂ 3 (1969-1972) carried an advanced navigation and The GWE, at the time the largest fully international locator communications system, a forerunner of the Global scientific experiment ever undertaken, linked in situ and Positioning System (GPS), that was used to track and inter- satellite data with computer modeling in an attempt to rogate neutral buoyancy balloons; it also opened up the pos- improve operational weather forecasting, determine the ulti- sibility of vertical temperature and water vapor soundings mate range of numerical weather prediction, and develop a and the ability to measure Earthâs radiation budget above the scientific basis for climate modeling and prediction. In this atmosphere, allowing for estimates of zonal poleward heat experiment, worldwide surface and upper-air observations transport. Nimbus 4 (1970-1980) flew spatially scanning from satellites, ships, land stations, aircraft, and balloons infrared sounders and collected global observations of the were combined with global coverage provided by two U.S. ozone layer. Nimbus 5 (1972-1983) carried microwave and GOES satellites, the European Meteosat, the Russian Geosta- stratospheric sounders, measured rainfall over the oceans, tionary Operational Meteorological Satellite (GOMS), and and mapped and monitored sea ice. Nimbus 6 (1975-1983) the Japanese GeoÂstationary Meteorological Satellite (GMS) improved measurements of atmospheric temperature at dif- (Figure 2.7). ferent altitudes. Launched into sun-synchronous polar orbit between The long-lived Nimbus 7 (1978-1994) carried the 1964 and 1978, the Nimbus series of seven satellites con- Coastal Zone Color Scanner (CZCS; see ChapterÂ 8), which tributed to our understanding of the atmosphere, land surface provided data until 1986; the Total Ozone Mapping Spec- and ecosystems, weather, and oceanography and constituted trometer (TOMS; see Chapter 5), which failed in 1993; and the nationâs âprimary research and development platform for six other improved versions of sensors previously flown. satellite remote-sensing of the Earthâ (Figure 2.9). Accord- The cavity radiometer aboard the Earth Radiation Budget ing to NASA, âEach mission taught scientists not only some- Experiment of the Nimbus 7 satellite provided the first pre- thing new about the Earth system, but also something new cise measurements of total solar irradiance reaching Earth. about how to create, operate, and improve the technology for The technology and lessons learned from the Nimbus mis- observing the Earth from spaceâ (NASA Earth Observatory, sions stand behind most of the Earth-observing satellites that http://earthobservatory.nasa.gov/Study/Nimbus/). NASA and NOAA have launched since 1978. Nimbus 1 (1964) provided the first global images NASAâs efforts in satellite geodesy date to 1962 when of clouds and large weather systems. Flying a medium- planning began for the National Geodetic Satellite Pro- resolution infrared radiometer, Nimbus 2 (1966-1969) gram, with the initial goal of developing âa unified world mapped the distribution of water vapor and carbon dioxide datum accurate to Â±10 m and to refine the description of in the atmosphere, measured the temperature of the ocean, the earthâs gravity field.â A satellite-based laser tracking FIGURE 2.7â During the GWE, five international geostationary satellites supported global observations of cloud-tracked winds. SOURCE: NOAA (1984).
EARTH OBSERVATIONS FROM SPACE: THE EARLY HISTORY 15 system immediately returned results of Â±1 m, which was an order-of-magnitude improvement, with an additional order- BOX 2.3 of-magnitude improvement possible (NASA 1970). Verner Edward Suomi (1915-1995) In 1978, based on its experience with planetary probes, JPL launched Seasat, an experimental satellite carrying a Verner Edward Suomi (Figure 2.8) was born in variety of oceanographic sensors, including imaging syn- Eveleth, Minnesota, received a Ph.D. in meteorology thetic aperture radar, altimeters, radiometers, and scatterom- from the University of Chicago and spent most of eters. The instruments measured ocean surface topography, his career at the University of Wisconsin, Madison, boundary-layer ocean wind speed and direction, sea surface where he was co-founder of the Space Science and temperature, and polar sea ice conditions. Although Seasat Engineering Center, a premier institution dedicated collected data for only 105 days, it inspired the future use to atmospheric research and instrument develop- of imaging radars on NASAâs Space Shuttle, Topography ment for satellites and other spacecraft. Experiment (TOPEX)/Poseidon, and a number of satellites Suomi is considered one of the founding fathers flown by the Europeans, Canadians, and Japanese. These of satellite meteorology. His innovations in scien- satellite-borne radars are able to detect minute changes in tific instrumentation, data processing, and analysis surface features due to tectonic, volcanic, hydrologic, or have substantially improved our understanding of anthropogenic activity. weather and climate. Suomiâs professional career combined inventiveness with a keen ability to mo- bilize human and financial resources in support of INSTRUMENT AND TECHNOLOGY DEVELOPMENT his ideas and projects. Although it carried no remote sensing instruments, the orbital decay of the first Earth satellite, Sputnik 1, provided information about the density and dangers of the near-space environment. The operation of its two radio transmitters provided clues regarding the electron density of the iono- sphere and indicated that the satelliteâs pressurized nitrogen compartment had not been punctured by micrometeorites (Hagfors and Schlegel 2001). Many observations of the Earth system from space have been conducted using optical sensors. TIROS 1 housed two television cameras and stored the information on magnetic tapes for later transmission to ground stations. TIROS 2 con- tained an infrared sensor in addition to the two cameras and a new attitude control system using Earthâs magnetic field. Subsequently, optical sensors were adapted for many differ- ent applications in all disciplines of the Earth sciences. Video cameras soon gave way to medium- and high-Âresolution radiometers in all wavelengths. TIROS 6, launched in 1962, made the first measurements of snow cover from space using infrared sensors. This technology is also used to observe sea ice coverage and the temperature of cloud tops and the sea surface. Since the atmosphere is virtually transparent to micro- wave radiation, these sensors can penetrate clouds to make ground measurements in all weather conditions. The first such passive microwave remote sensing system for satel- lites was launched on the Russian Cosmos 243 (1968) and Cosmos 384 (1970) (Johannessen et al. 2001). The Electri- cally Scanning Microwave Radiometer (ESMR) was flown on Nimbus 5 (1972-1983) over the Arctic to detect sea ice coverage, where cloud cover frequently interfered with infra- FIGURE 2.8â Verner Edward Suomi. SOURCE: Uni- versity of Wisconsin-Madison. Reprinted with per- red technology. Subsequently, this technology was further mission by the University of Wisconsin, Madison. developed, and the Scanning Multichannel Microwave Radi- ometer (SMMR) on Nimbus 7 (1978-1994), together with the Defense Meteorological Satellite Program (DMSP) Special
16 EARTH OBSERVATIONS FROM SPACE: THE FIRST 50 YEARS OF SCIENTIFIC ACHIEVEMENTS Sensor Microwave/Imager (SSM/I), have provided the longest and most regular time series of global sea ice data at a resolution of typically 25 Ã 25 km (Johannessen et al. 2001). Moreover, the microwave radiation emitted by atmospheric oxygen and water vapor were used for vertical soundings, espe- cially in the upper atmosphere. In 1972, ERTS 1 (Earth Resources Technology Satellite), later renamed Landsat 1, provided new land-based applications for optical sensors. Land- sat carried a return beam videocon (RBV) and a multispectral scanner (MSS) that imaged Earth from an alti- tude of 900 km with green, red, and two infrared spectral bands at 80-m resolution. Since 1972, Landsats have provided the longest, continuous global record of land cover and its historical changes in existence. Landsat is the premier technology supporting the new geographical field of land-cover sci- ence, part of Earth system science. In the 1970s, laser technology was first employed in combination with sat- ellites (Laser Geodynamics Satellites [LAGEOS] 1 and 2) that were designed for maximum reflectivity to allow for study of Earthâs geoid and the move- ments of tectonic plates. Interestingly, this type of satellite does not contain any instrumentation, and for that reason the first such satellite launched in 1976 is still operational today. Spaceborne synthetic aperture radar enables obser- vation of sea ice with much better accu- racy than visible and passive microwave FIGURE 2.9â Artistâs drawing of the general design of the Nimbus series of satellites. SOURCE: C. R. Madrid, ed. (1978). The ÂNimbusÂ 7 Usersâ Guide, Goddard Space Flight methods, as proven by Seasat, the Euro- Center, NASA. pean Remote Sensing Satellite (ERS 1), Canadaâs RADARSAT, and Europeâs Envisat (Figure 2.10) (Johannessen et al. 2001). Although Seasat was able to collect data only for CONCLUSION 105 days, it pioneered the exploitation of radar technology and the microwave range to measure ocean topography and In the first two decades of the space age, six nations winds. Its success led to important follow-on missions such designed and launched Earth-orbiting satellites for scientific as Topex/Poseidon and QuikScat. purposes: the Soviet Union (1957), the United States (1958), France (1965), Japan (1970), China (1970), and the United Kingdom (1971). The European Space Agency, a consortium of 17 member nations, was founded in 1974. International cooperation has been an important aspect of the satellite legacy: the Global Weather Experiment (1979) demonstrated what was possible in observation, modeling, understanding, The projected lifetime of the LAGEOS satellites is more than 200,000 and prediction. Today, such experiments are conducted every years.
EARTH OBSERVATIONS FROM SPACE: THE EARLY HISTORY 17 in 1957 was not real, and the militarization of space, for- tunately, has not happened yet. International cooperation, rather than competition, has become the dominant theme in the space age, not only in satellite hardware but also in creative analysis and use of satellite data. Just what would the world be like without scientific satellite remote sensing and services? It would be much like 1957. The Moon would be Earthâs only satellite. There would be no weather eyes in the skyâno global ability to monitor changes in atmospheric composition, in ecosystems and land use, in climate variabil- ity and change, in Earthâs surface and land-use changes, in ocean physical and biological processes, or in ice sheets. The complexity of todayâs bureaucratic and budgetary practices has created a time delay problem. Many of the expert consultants who made presentations to this com- mittee mentioned the ease of moving among agencies and programs in the early days and how new ideas were rapidly tested and research results found quick expression in opera- tional systems. The ideas generated by Wexler, Van Allen, Suomi, and others were well supported and well funded, with comparative ease. The ferment of ideas was supported by rapid development and short time lags between concept and launch. This no longer seems to be the case. A final issue derives from findings of the National Acad- emiesâ recent decadal survey of Earth science missions that reports an actual âsatellite gapâ in which space resources will decrease dramatically compared to the scientific challenges FIGURE 2.10â Detail of sea ice off the west coast of Greenland associated with, for example, climate change research. These from ERS 1. SOURCE: ERS-1 User Handbook, SP-1148, European satellite data gaps also stand in stark contrast to the stun- Space Agency, Paris. Reprinted with permission by the European ning and growing needs for space-based information by the Space Agency. worldâs inhabitants (NRC 2007a). At the dawn of the space age, the very first satellites provided new and important scientific knowledge of the dayânot just for the weather but to explore and monitor all Earth system that could not be obtained by any other means. components of the Earth system. International cooperation The first two decades were extremely exciting, yet new dis- has other dimensions as well. When the U.S. GOES-W sat- coveries, transformative breakthroughs, proof of concepts, ellite failed in 1989, it was replaced by a French Meteosat. improved understanding, and societal benefits have contin- From 2003 to 2005, GOES 9 was on loan to Japan to cover a ued to accumulate, as the following chapters in this report significant gap in Japanâs meteorological satellite coverage. document. How can we compare the cumulative amount Our imperfect appreciation of how much has been spent by the nations of the world on the scientific study of accomplished in the past 50 years may well reflect a gap in Earth from space with the inestimable value of understanding historical comprehension. The âmissile gapâ widely feared our home planet?