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Earth Observations from Space: The First 50 Years of Scientific Achievements 2 Earth Observations from Space: The Early History “Space technology affords new opportunities for scientific observation and experiment, which will add to our knowledge and understanding of the earth.” —President’s Science Advisory Committee (1958) The space age officially began on October 4, 1957, with the dramatic and historic launch of Sputnik 1 by the Soviet Union, but there are much deeper roots. Robert H. Goddard developed liquid-fueled rockets and used them for weather photography in the 1920s; remote sensing radio technology was developed in the 1930s and 1940s; a V-2 rocket flight in 1947 photographed clouds from an altitude of 100 miles; and by 1954 instrumented sounding rockets had serendipitously photographed an unknown tropical storm (Figure 2.1). FIGURE 2.1 Image of a previously undetected tropical storm in the Gulf of Mexico photographed by an Aerobee sounding rocket in 1954. SOURCE: Hubert and Berg (1955). Reprinted with permission from the American Meteorological Society, copyright 1955. In 1955 the United States announced it would launch a scientific Earth satellite during the International Geophysical Year (IGY) of 1957-1958. Sputnik, however, diverted the world’s attention from scientific concerns and focused American perceptions on a “missile gap” and possible national security threats from space. The November launch of Sputnik 2 further fueled these fears. In response, and with the Navy’s Vanguard Program languishing, the U.S. Department of Defense used a modified Redstone military missile, the Juno 1, to launch the first U.S. satellite, Explorer 1, on January 31, 1958. That year Congress enacted the National Defense Education Act, which provided dramatically increased support for both basic research and science education at all levels and benefited the nation in subsequent generations in ways that could not have been foreseen at the time. The National Aeronautics and Space Act created a new agency—the National Aeronautics and Space Administration (NASA)—to 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 President’s Science Advisory Committee pointed out that a satellite in orbit could be used for three scientific purposes: “(1) it can sample the strange new environment though which it moves; (2) it can look down and see the earth as it has never been seen before; and (3) it can look out into the universe and record informa-
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Earth Observations from Space: The First 50 Years of Scientific Achievements tion that can never reach the earth’s surface because of the intervening atmosphere” (PSAC 1958). Even in 1958, scientists knew that Earth-orbiting satellites would encounter and be able to measure the charged plasma of the solar wind, the three-dimensional structure of Earth’s gravitational and magnetic fields, and other energy fluxes and fast-moving particles in near space. Satellites could detect incoming cosmic rays and be used to test Einstein’s general theory of relativity; they could measure solar energy at the top of the atmosphere to determine how much is reflected and radiated back to space by clouds, oceans, continents, and ice sheets; and they could look down at Earth to expand surveillance of weather systems from about 10 percent to practically 100 percent of Earth’s surface. The scientific accomplishments of five prominent early satellites (Explorer 1, Explorer 7, TIROS 1 [Television Infrared Observing Satellite], ATS 1 [Application Technology Satellite], and the Nimbus series), all launched in the first two decades of the space age, fulfilled many of these expectations. EARLY SATELLITES AND PIONEERS “At the dawn of the Space Age, the nature of space exploration was already apparent: It always leads to unexpected discoveries about our universe and the processes that shape our environment” (Friedman 2006). On May 1, 1958, University of Iowa scientist James Van Allen (Box 2.1, Figure 2.2) announced that Geiger-Müller 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 (O’Keefe et al. 1960). NASA launched the world’s 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 “storm patrol” 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 changes occurring during cyclogenesis. In a posthumous article published in 1965, Harry Wexler (Box 2.2, Figure 2.6) wrote, “The TIROS satellites disclosed the existence of storms in areas where few or no observations previously existed, revealed unsuspected structures of storms even in BOX 2.1 James A. Van Allen (1914-2006) James A. Van Allen (Figure 2.2) was born in Mount Pleasant, Iowa; he earned a Ph.D. in physics from the University of Iowa and spent almost his entire career there in the Department of Physics and Astronomy. During World War II he served in the Navy, working at the Carnegie Institution of Washington and the Johns Hopkins University Applied Physics Laboratory, where he helped develop and test the radio proximity fuse. After the war he developed instrument packages for upper-atmosphere and near-space scientific exploration and was head of development for the Aerobee sounding rocket. In 1950, Van Allen hosted a dinner at his home where plans were initiated for the IGY—a coordinated, international, and comprehensive study of Earth 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 model of Earth. Van Allen subsequently served as principal investigator for more than 25 space science missions. He was active in NASA, National Academy of Sciences, and American Geophysical Union affairs and was an articulate and outspoken advocate of small, inexpensive space missions. FIGURE 2.2 James A. Van Allen, in his office on the University of Iowa campus in Iowa City, 1990. SOURCE: Photo by Tom Jorgensen, University of Iowa. Reprinted with permission from Tom Jorgensen, University of Iowa.
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Earth Observations from Space: The First 50 Years of Scientific Achievements FIGURE 2.3 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 Army’s Redstone Arsenal team. SOURCE: Jet Propulsion Laboratory. FIGURE 2.4 TIROS 1 and technician. SOURCE: National Archives Photo 370-MSP-4-147. FIGURE 2.5 TIROS 1: first TV picture of weather from space, April 1, 1960. SOURCE: NASA. areas of extensive observational coverage, depicted snow fields over land, ice floes over water, and temperature patterns on land and ocean as well as temperatures of tops of cloud layers.” Because its accomplishments were clearly accessible to the general public, the TIROS program enjoyed strong political 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, Explorer 7 carried a number of instruments including solar X-ray, Lyman-alpha, cosmic radiation, and micrometeor detectors. Significantly, it also carried University of Wisconsin, Madison scientist Verner Suomi’s (Box 2.3, Figure 2.8) improved radiometer, which took the first Earth radiation measurements from space and initiated the era of satellite studies of climate. These observations established that Earth’s energy budget varies markedly due to the effect of clouds and other absorbing constituents (Suomi 1961). Beginning in 1963, in collaboration with Robert Parent, Suomi developed a spin-stabilized camera that continuously
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Earth Observations from Space: The First 50 Years of Scientific Achievements BOX 2.2 Harry Wexler (1911-1962) Harry Wexler (Figure 2.6) was born in Fall River, Massachusetts, and earned a Ph.D. in meteorology from the Massachusetts Institute of Technology under C. G. Rossby. He spent most of his career with the U.S. Weather Bureau and also served as an instructor of military weather cadets during World War II. As head of research for the Weather Bureau, Wexler participated in the development of a number of new technologies, including airborne observations, sounding rockets, radar, the use of electronic computers for numerical weather prediction and general circulation studies, and satellite meteorology. He also served as chief scientist for the U.S. expedition to the Antarctic for the IGY and established a number of atmospheric baseline measurements of trace gases, including carbon dioxide and ozone. From the early 1950s, Wexler promoted the use of satellites in meteorology. Wexler, who played a central role in the development of Explorer and TIROS, foresaw that information gathered from satellites would be of great value for severe weather warnings, measurement of Earth’s heat budget, and detection of environmental changes, both immediate and long term. Always interested in global studies of weather and climate, Wexler was an enthusiastic promoter of the World Weather Watch, which became a reality in 1963, shortly after his death. FIGURE 2.6 Harry Wexler. SOURCE: Wexler and J. E. Caskey, Jr. (1963). North-Holland Publishing Co., Amsterdam, 1963. monitored the weather and its motions over a large fraction of Earth’s surface. Their “spin-scan camera” first flew on NASA’s ATS 1, a spin-stabilized communications satellite launched into geostationary orbit in December 1966 (Suomi et al. 1971). Suomi’s “gadget,” as he called all his inventions, produced spectacular full-disk images of Earth. It allowed scientists to observe weather systems as they developed, instead of glimpsing small bits at odd intervals, and it provided the first full-Earth disk: high-quality, cloud-cover pictures taken from a geostationary satellite. The image had a resolution of about 3 km and allowed meteorologists to identify and study significant cloud patterns, including those in the tropics, their change with time, the structure of storms, and the way synoptic-scale weather interacted with local phenomena. The spin-scan system, used in conjunction with ground and tropospheric balloon observations, also contributed to quantitative measurements of the dynamics of air motion, cloud heights, and the amount of atmospheric pollution. Using the communications capabilities of ATS 1, NASA was able to send cloud images and weather data to ground stations in the United States, Canada, Japan, Australia, and islands in the Pacific. The weather satellite images seen today on worldwide television and the Internet are direct descendents of Suomi’s invention. They are essential for warning the public of tropical storm landfalls and other potential natural disasters. A color version of the spin-scan camera flew on ATS 3 in 1967. It was used to detect the genesis of severe storms in the American Midwest, document the complete life cycle of hurricanes, and support the Barbados Oceanographic and Meteorological Experiment (BOMEX) study of energy exchanges between the ocean and the atmosphere. Subsequent 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 13 Geostationary Operational Environmental Satellites (GOES) launched since 1975. These experiments enabled Suomi and his team to document that Earth absorbed more of the Sun’s energy than originally thought and to demonstrate that it was possible to measure and quantify seasonal changes in the global heat budget. One of Suomi’s 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 instruments, ground-based radar, and conventional and automated meteorological stations (Chatters and Suomi 1975). It was 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
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Earth Observations from Space: The First 50 Years of Scientific Achievements the First GARP Global Experiment, subsequently known as the Global Weather Experiment (GWE), 1977-1979. The GWE, at the time the largest fully international scientific experiment ever undertaken, linked in situ and satellite data with computer modeling in an attempt to improve operational weather forecasting, determine the ultimate range of numerical weather prediction, and develop a scientific basis for climate modeling and prediction. In this experiment, worldwide surface and upper-air observations from satellites, ships, land stations, aircraft, and balloons were combined with global coverage provided by two U.S. GOES satellites, the European Meteosat, the Russian Geostationary Operational Meteorological Satellite (GOMS), and the Japanese Geostationary Meteorological Satellite (GMS) (Figure 2.7). Launched into sun-synchronous polar orbit between 1964 and 1978, the Nimbus series of seven satellites contributed to our understanding of the atmosphere, land surface and ecosystems, weather, and oceanography and constituted the nation’s “primary research and development platform for satellite remote-sensing of the Earth” (Figure 2.9). According to NASA, “Each mission taught scientists not only something new about the Earth system, but also something new about how to create, operate, and improve the technology for observing the Earth from space” (NASA Earth Observatory, http://earthobservatory.nasa.gov/Study/Nimbus/). Nimbus 1 (1964) provided the first global images of clouds and large weather systems. Flying a medium-resolution infrared radiometer, Nimbus 2 (1966-1969) mapped the distribution of water vapor and carbon dioxide in the atmosphere, measured the temperature of the ocean, and clearly revealed the outlines of major ocean currents. Nimbus 3 (1969-1972) carried an advanced navigation and locator communications system, a forerunner of the Global Positioning System (GPS), that was used to track and interrogate neutral buoyancy balloons; it also opened up the possibility of vertical temperature and water vapor soundings and the ability to measure Earth’s radiation budget above the atmosphere, allowing for estimates of zonal poleward heat transport. Nimbus 4 (1970-1980) flew spatially scanning infrared sounders and collected global observations of the ozone layer. Nimbus 5 (1972-1983) carried microwave and stratospheric sounders, measured rainfall over the oceans, and mapped and monitored sea ice. Nimbus 6 (1975-1983) improved measurements of atmospheric temperature at different altitudes. The long-lived Nimbus 7 (1978-1994) carried the Coastal Zone Color Scanner (CZCS; see Chapter 8), which provided data until 1986; the Total Ozone Mapping Spectrometer (TOMS; see Chapter 5), which failed in 1993; and six other improved versions of sensors previously flown. The cavity radiometer aboard the Earth Radiation Budget Experiment of the Nimbus 7 satellite provided the first precise measurements of total solar irradiance reaching Earth. The technology and lessons learned from the Nimbus missions stand behind most of the Earth-observing satellites that NASA and NOAA have launched since 1978. NASA’s efforts in satellite geodesy date to 1962 when planning began for the National Geodetic Satellite Program, with the initial goal of developing “a unified world datum accurate to ±10 m and to refine the description of the earth’s gravity field.” A satellite-based laser tracking FIGURE 2.7 During the GWE, five international geostationary satellites supported global observations of cloud-tracked winds. SOURCE: NOAA (1984).
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Earth Observations from Space: The First 50 Years of Scientific Achievements BOX 2.3 Verner Edward Suomi (1915-1995) Verner Edward Suomi (Figure 2.8) was born in Eveleth, Minnesota, received a Ph.D. in meteorology from the University of Chicago and spent most of his career at the University of Wisconsin, Madison, where he was co-founder of the Space Science and Engineering Center, a premier institution dedicated to atmospheric research and instrument development for satellites and other spacecraft. Suomi is considered one of the founding fathers of satellite meteorology. His innovations in scientific instrumentation, data processing, and analysis have substantially improved our understanding of weather and climate. Suomi’s professional career combined inventiveness with a keen ability to mobilize human and financial resources in support of his ideas and projects. FIGURE 2.8 Verner Edward Suomi. SOURCE: University of Wisconsin-Madison. Reprinted with permission by the University of Wisconsin, Madison. system immediately returned results of ±1 m, which was an order-of-magnitude improvement, with an additional order-of-magnitude improvement possible (NASA 1970). In 1978, based on its experience with planetary probes, JPL launched Seasat, an experimental satellite carrying a variety of oceanographic sensors, including imaging synthetic aperture radar, altimeters, radiometers, and scatterometers. The instruments measured ocean surface topography, boundary-layer ocean wind speed and direction, sea surface temperature, and polar sea ice conditions. Although Seasat collected data for only 105 days, it inspired the future use of imaging radars on NASA’s Space Shuttle, Topography Experiment (TOPEX)/Poseidon, and a number of satellites flown by the Europeans, Canadians, and Japanese. These satellite-borne radars are able to detect minute changes in surface features due to tectonic, volcanic, hydrologic, or anthropogenic activity. INSTRUMENT AND TECHNOLOGY DEVELOPMENT 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 ionosphere and indicated that the satellite’s 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 contained an infrared sensor in addition to the two cameras and a new attitude control system using Earth’s magnetic field. Subsequently, optical sensors were adapted for many different applications in all disciplines of the Earth sciences. Video cameras soon gave way to medium- and high-resolution 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 microwave radiation, these sensors can penetrate clouds to make ground measurements in all weather conditions. The first such passive microwave remote sensing system for satellites was launched on the Russian Cosmos 243 (1968) and Cosmos 384 (1970) (Johannessen et al. 2001). The Electrically 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 infrared technology. Subsequently, this technology was further developed, and the Scanning Multichannel Microwave Radiometer (SMMR) on Nimbus 7 (1978-1994), together with the Defense Meteorological Satellite Program (DMSP) Special
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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 × 25 km (Johannessen et al. 2001). Moreover, the microwave radiation emitted by atmospheric oxygen and water vapor were used for vertical soundings, especially in the upper atmosphere. In 1972, ERTS 1 (Earth Resources Technology Satellite), later renamed Landsat 1, provided new land-based applications for optical sensors. Landsat carried a return beam videocon (RBV) and a multispectral scanner (MSS) that imaged Earth from an altitude 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 science, part of Earth system science. In the 1970s, laser technology was first employed in combination with satellites (Laser Geodynamics Satellites [LAGEOS] 1 and 2) that were designed for maximum reflectivity to allow for study of Earth’s geoid and the movements 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.1 Spaceborne synthetic aperture radar enables observation of sea ice with much better accuracy than visible and passive microwave methods, as proven by Seasat, the European Remote Sensing Satellite (ERS 1), Canada’s RADARSAT, and Europe’s Envisat (Figure 2.10) (Johannessen et al. 2001). Although Seasat was able to collect data only for 105 days, it pioneered the exploitation of radar technology and the microwave range to measure ocean topography and winds. Its success led to important follow-on missions such as TOPEX/Poseidon and QuikScat. FIGURE 2.9 Artist’s drawing of the general design of the Nimbus series of satellites. SOURCE: C. R. Madrid, ed. (1978). The Nimbus 7 Users’ Guide, Goddard Space Flight Center, NASA. CONCLUSION In the first two decades of the space age, six nations designed and launched Earth-orbiting satellites for scientific 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, and prediction. Today, such experiments are conducted every 1 The projected lifetime of the LAGEOS satellites is more than 200,000 years.
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Earth Observations from Space: The First 50 Years of Scientific Achievements FIGURE 2.10 Detail of sea ice off the west coast of Greenland from ERS 1. SOURCE: ERS-1 User Handbook, SP-1148, European Space Agency, Paris. Reprinted with permission by the European Space Agency. day—not just for the weather but to explore and monitor all components of the Earth system. International cooperation has other dimensions as well. When the U.S. GOES-W satellite failed in 1989, it was replaced by a French Meteosat. From 2003 to 2005, GOES 9 was on loan to Japan to cover a significant gap in Japan’s meteorological satellite coverage. Our imperfect appreciation of how much has been accomplished in the past 50 years may well reflect a gap in historical comprehension. The “missile gap” widely feared in 1957 was not real, and the militarization of space, fortunately, 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 Earth’s only satellite. There would be no weather eyes in the sky—no global ability to monitor changes in atmospheric composition, in ecosystems and land use, in climate variability and change, in Earth’s surface and land-use changes, in ocean physical and biological processes, or in ice sheets. The complexity of today’s bureaucratic and budgetary practices has created a time delay problem. Many of the expert consultants who made presentations to this committee 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 operational 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 Academies’ recent decadal survey of Earth science missions that reports an actual “satellite gap” in which space resources will decrease dramatically compared to the scientific challenges associated with, for example, climate change research. These satellite data gaps also stand in stark contrast to the stunning and growing needs for space-based information by the world’s inhabitants (NRC 2007a). At the dawn of the space age, the very first satellites provided new and important scientific knowledge of the Earth system that could not be obtained by any other means. The first two decades were extremely exciting, yet new discoveries, transformative breakthroughs, proof of concepts, improved understanding, and societal benefits have continued to accumulate, as the following chapters in this report document. How can we compare the cumulative amount spent by the nations of the world on the scientific study of Earth from space with the inestimable value of understanding our home planet?