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NASA: A Knowledge Agency

INTRODUCTION

The mission of the National Aeronautics and Space Administration (NASA) is—

  • To advance and communicate scientific knowledge and understanding of the Earth, the solar system, and the universe.

  • To advance human exploration, use, and development of space.

  • To research, develop, verify, and transfer advanced aeronautics and space technologies.1

NASA’s program is divided into five strategic enterprises: (1) Aerospace Technology, (2) Biological and Physical Research, (3) Earth Science, (4) Human Exploration and Development of Space, and (5) Space Science.2 This report is concerned with the Earth Science and Space Science Enterprises. Both enterprises collect large volumes of data from spaceborne instruments, either to study changes in the oceans, atmosphere, and land surface of the Earth or to explore the universe and search for life beyond the Earth. Managing the data collected from these missions in order to further scientific understanding now and in the future is an enormous challenge.

The Task Group on the Usefulness and Availability of NASA’s Space Mission Data was charged by NASA’s associate administrators for earth science and space science to (1) evaluate the availability and accessibility of data from earth and space science missions, (2) determine the usefulness of NASA’s data collections for supporting scientific studies, and (3) assess whether the balance between attention to mission planning and implementation versus data analysis and utilization is appropriate. (The complete charge is presented in Appendix A.) This report reviews the data systems, services, and strategies for managing earth and space science data collected from space. (The stages in collecting data, from planning a mission to long-term maintenance of data, are described in Appendix B.) Chapter 1 explores the goals of several of the earth and space science disciplines that rely on NASA missions, and it describes how data are used to achieve important science objectives. Chapter 2 describes how the data are currently managed and evaluates the effectiveness of these management strategies. The focus is on the 16 major data facilities and data services that have significant holdings (e.g., at least 1 terabyte) or budgets (e.g., more than $1 million), or are intended to operate for many years. The major data facilities include active archives, which hold data that are being used intensively for research, and data centers, which maintain data that will continue to be used in the future. (Information asked of

1  

National Aeronautics and Space Administration, 2000, NASA 2000 Strategic Plan, Washington, D.C., 72 pp.

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See <http://www.nasa.gov >.



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Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data 1 NASA: A Knowledge Agency INTRODUCTION The mission of the National Aeronautics and Space Administration (NASA) is— To advance and communicate scientific knowledge and understanding of the Earth, the solar system, and the universe. To advance human exploration, use, and development of space. To research, develop, verify, and transfer advanced aeronautics and space technologies.1 NASA’s program is divided into five strategic enterprises: (1) Aerospace Technology, (2) Biological and Physical Research, (3) Earth Science, (4) Human Exploration and Development of Space, and (5) Space Science.2 This report is concerned with the Earth Science and Space Science Enterprises. Both enterprises collect large volumes of data from spaceborne instruments, either to study changes in the oceans, atmosphere, and land surface of the Earth or to explore the universe and search for life beyond the Earth. Managing the data collected from these missions in order to further scientific understanding now and in the future is an enormous challenge. The Task Group on the Usefulness and Availability of NASA’s Space Mission Data was charged by NASA’s associate administrators for earth science and space science to (1) evaluate the availability and accessibility of data from earth and space science missions, (2) determine the usefulness of NASA’s data collections for supporting scientific studies, and (3) assess whether the balance between attention to mission planning and implementation versus data analysis and utilization is appropriate. (The complete charge is presented in Appendix A.) This report reviews the data systems, services, and strategies for managing earth and space science data collected from space. (The stages in collecting data, from planning a mission to long-term maintenance of data, are described in Appendix B.) Chapter 1 explores the goals of several of the earth and space science disciplines that rely on NASA missions, and it describes how data are used to achieve important science objectives. Chapter 2 describes how the data are currently managed and evaluates the effectiveness of these management strategies. The focus is on the 16 major data facilities and data services that have significant holdings (e.g., at least 1 terabyte) or budgets (e.g., more than $1 million), or are intended to operate for many years. The major data facilities include active archives, which hold data that are being used intensively for research, and data centers, which maintain data that will continue to be used in the future. (Information asked of 1   National Aeronautics and Space Administration, 2000, NASA 2000 Strategic Plan, Washington, D.C., 72 pp. 2   See <http://www.nasa.gov >.

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Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data these facilities in a questionnaire is listed in Appendix C.) The satisfaction of the users, who ultimately judge the success of the system, is discussed in Chapter 3. Chapter 4 then examines some new approaches for increasing the availability and usefulness of earth and space science data, discusses the balance between mission operations and data analysis, and makes some recommendations about how to meet the data challenges of the next decade. Background information, including biographical information on task group members (Appendix D), meeting agendas (Appendix E), and an acronym list (Appendix F) appear at the end of the report. SPACE SCIENCE ENTERPRISE The science objectives of NASA’s Space Science Enterprise are to “solve mysteries of the universe, explore the solar system, discover planets around other stars, search for life beyond Earth from origins to destiny, chart the evolution of the universe and understand its galaxies, stars, planets, and life.”3 The Space Science Enterprise, managed by the Office of Space Science (OSS), is divided into four science themes: (1) origins, which seeks to understand where we come from and whether we are alone; (2) the structure and evolution of the universe; (3) the Sun-Earth connection; and (4) solar system exploration. Examples of the science programs and their interactions with data sets are described below. Astrophysics: Origins and the Structure and Evolution of the Universe NASA missions have opened up new windows on the universe, vastly increasing our knowledge about the world around us. Astrophysical sources, collectively, radiate across the spectrum: from gamma rays and X-rays, through the visible and infrared, all the way to microwaves and long-wavelength radio waves. Much of this radiation does not penetrate the Earth’s atmosphere and can be studied only from space. NASA’s scientific priorities for future missions, developed in coordination with the research community,4 include: Understand the structure of the universe, from its earliest beginnings to its ultimate fate; Explore the ultimate limits of gravity and energy in the universe; Learn how galaxies, stars, and planets form, interact, and evolve.5 Even modest success in achieving these goals would constitute a spectacular advance in human understanding, and NASA has become an acknowledged leader in this exciting venture. The program seeks to address “the most fundamental questions that science can ask: how the universe began and is changing, what are the past and future of humanity, and whether we are alone. In taking up these questions, researchers and the general public—for we are all seekers in this quest—will draw upon all areas of science and the technical arts.”6 3   National Aeronautics and Space Administration, 2000, The Space Science Enterprise Strategic Plan, Washington, D.C., 127 pp. 4   Review of NASA’s Office of Space Science Strategic Plan 2000, letter to Edward J.Weiler, Associate Administrator for NASA’s Office of Space Science, National Research Council, Washington, D.C., June 1, 2000. 5   National Aeronautics and Space Administration, 2000, The Space Science Enterprise Strategic Plan, Washington, D.C., 127 pp. 6   National Aeronautics and Space Administration, 2000, The Space Science Enterprise Strategic Plan, Washington, D.C., 127 pp.

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Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data The goals outlined above require that data be accessible in a form useful to the science community, that is, calibrated and maintained in accessible data facilities, along with tools for analyzing and visualizing the data. As stated in the 2000 OSS Strategic Plan: Vast amounts of data are returned from space science missions. The volume, richness and complexity of the data, as well as the need to integrate and correlate data from multiple missions into a larger context for analysis and understanding, present growing opportunities. Exploration and discovery using widely distributed, multi-terabyte databases will challenge all aspects of data management and rely heavily on the most advanced analysis and visualization tools. The design and implementation of the next generation of information systems will depend on close collaboration between space science and computer science and technology.7 To achieve its objectives, NASA is flying or plans to fly an ambitious suite of missions (see Table 1.1), with still more to come (e.g., Next Generation Space Telescope, Space Interferometry Mission, and Constellation X). The missions illustrate the diversity of fields that will contribute to the goals of the strategic plan (cosmic rays, nature of high-energy sources, star formation in galaxies, dark matter, cosmology). The diversity of the science and the associated experimental approach lead to a wide range in types of data (time-tagged event logging, multispectral images, and spectroscopy, among others), and each data set and its archive will naturally have different characteristics and requirements. With the launch of new missions, the volume of astrophysics data will increase substantially, and the demand to compile federated data sets—that is, data sets that can be accessed, intercompared, and queried simultaneously—from different missions will increase. For example, the Galaxy Evolution Explorer (GALEX) is designed to measure the ultraviolet light emitted directly from populations of hot, young stars in galaxies. Some of this ultraviolet light is absorbed by dust grains in interstellar space in the galaxies and is re-emitted as infrared radiation. One of the goals of the Space Infrared Telescope Facility (SIRTF) is to measure that reradiated energy. Thus, a combination of GALEX and SIRTF observations is needed to obtain a comprehensive picture of the cycling of interstellar gas through stars. That information, in turn, is needed to achieve an understanding of how galaxies were formed and how they have evolved. It is clear that the science will require databases that facilitate combining not just GALEX and SIRTF data, but data from other ultraviolet and infrared missions as well as data at other wavelengths. The Hubble Space Telescope (HST) is one of the most powerful tools ever built for astronomy, and it continues to produce spectacular results. Several generations of instruments on HST will have been deployed during its expected 20-year lifetime. Data are calibrated and held by the Space Telescope Science Institute (see Chapter 2), along with data from several other past and current missions and ground-based surveys. With the accumulation of new observations, research based on mining the HST active archives—often for studies quite different from those originally conceived—has increased at a rapid rate. Archival research now accounts for a substantial fraction of all HST research. Data are now retrieved from the HST active archive at a rate four times higher than that at which new data are put into the archive (see Figure 1.1). The growing number of data sets from diverse missions makes it possible to tackle important scientific problems in new ways, both by combining measurements from different missions and by taking advantage of the time baselines covered by the data (see Box 1.1). 7   National Aeronautics and Space Administration, 2000, The Space Science Enterprise Strategic Plan, Washington, D.C., p. 90.

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Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data TABLE 1.1 Selected U.S.-Led Astrophysics Missions Mission Objective Current Missions Chandra X-ray Observatory (CXO) Observes X-rays from high-energy regions of the universe, such as the remnants of exploding stars. Far-Ultraviolet Spectroscopic Explorer (FUSE) Explores the universe using high-resolution spectroscopy in the far-ultraviolet spectral region. High Energy Transient Explorer 2 (HETE-2) Detects and localizes gamma-ray bursts. Hubble Space Telescope (HST) Provides detailed images of celestial objects at high resolution. Microwave Anisotropy Probe (MAP) Measures the temperature of the cosmic background radiation over the full sky. Submillimeter Wave Astronomy Satellite (SWAS) Measures the amount of water, molecular oxygen, carbon monoxide, and atomic carbon in interstellar clouds. Upcoming Missions Advanced Cosmic Ray Composition Experiment for the Space Station (ACCESS) Study cosmic rays of very high energy to understand elementary particles in our galaxy. Galaxy Evolution Explorer (GALEX) Measure the ultraviolet light emitted directly from populations of hot, young stars in galaxies. Space Infrared Telescope Facility (SIRTF) Measure astrophysical phenomena at infrared wavelengths. Swift Gamma Ray Burst Explorer (Swift) Discover, detect, and study gamma-ray bursts. SOURCE: <http://spacescience.nasa.gov/missions/index.htm>.

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Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data FIGURE 1.1 Data flow into (dark gray) and out of (light gray) the Hubble Space Telescope mission archive, 1995–2001. Note that data flow out of the archive at a rate about four times higher than that of ingest. The increase in this ratio over time is the result of a growth in archival research. If data were used only by the principal investigator, as was true in the first few years after the launch of the HST, the ratio of data retrievals to ingest rate would be close to 1. SOURCE: Ethan Schreier, Space Telescope Science Institute.

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Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data BOX 1.1 Importance of Astrophysics Archives Examples of the role of NASA’s astrophysics archives in advancing knowledge include the following: The Cosmic Background Explorer flew in 1989–1990 and was successful in detecting large-scale fluctuations in the microwave background radiation. The character of the fluctuations matched theoretical predictions for structure on those scales emerging from the Big Bang, thereby providing a keystone in the field of cosmology.1 Two of the instruments, the Diffuse Infrared Background Experiment and the Far-Infrared Absolute Spectrometer, collected data that were subsequently mined from the archives for another purpose: to detect infrared light from galaxies at cosmological distances. This measurement demonstrated that substantial amounts of material had undergone nuclear processing inside massive stars and that substantial nucleosynthesis occurred at large redshift—that is, when the universe was very young. Much of the star-forming activity at large redshifts was shrouded behind dense clouds of interstellar dust. Thus important results were derived from archival research using data from an experiment designed for other purposes. The first evidence that the expansion of the universe is accelerating was reported in 1998.2 The basic observation is that distant supernovas appear dimmer than expected for a uniform rate of expansion. Alternative explanations have been proposed, including the possibility that distant supernovas are dimmed by intervening dust that absorbs all wavelengths equally and that does not betray its existence by making distant objects look redder. In order to rule out this possibility, astronomers searched archives for, and found, the most distant known supernova in the image of longest exposure ever taken by the Hubble Space Telescope. They then found that this same supernova had been observed in several other archived HST images and were able to show that it was twice as bright as it would have been if intergalactic dust or evolutionary effects were responsible for the dimming. This result, which requires that the universe be filled with some kind of mysterious “dark energy,” is probably the most significant cosmological discovery since the detection of the cosmic microwave background radiation. A particularly important example of research based on data stored in the active archives is the work stimulated by the observations of the Hubble Deep Fields. Designed to obtain images of the faintest objects observable with HST, long exposures were obtained of two small patches of the sky, one in the Northern Hemisphere and one in the Southern Hemisphere. Some of the galaxies seen in these images are at a distance of 12 billion light years; they are being seen as they were when the universe was only about 10 percent of its current age. These data allow astronomers to probe the characteristics of galaxies when they were just coming into existence. The observations were made available to the community as soon as they were reduced, with no proprietary period. Additional observations have now been obtained, either by spectroscopy or measurements at other wavelengths, by every major observatory in the world, both in space (e.g., by the Chandra X-ray Observatory, X-ray Multi-Mirror Mission, and Infrared Space Observatory) and on the ground (e.g., Wm. Keck Observatory, Very Large Array, and James Clerk Maxwell Telescope), and more than 200 follow-on papers have been published. 1   C.L.Bennett et al., 1996, Four-year COBE DMR cosmic microwave background observations: Maps and basic results, Astrophysical Journal Letters, v. 464, p. L1, and references therein. 2   A.G.Riess, 1998, Observational evidence for supernovae for an accelerating universe and a cosmological constant. Astronomical Journal, v. 116, p. 1009; S.Perlmutter, Measurements of omega and lambda from 42 high-redshift supernovae, Astrophysical Journal, v. 517, p. 565.

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Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data The Sun-Earth Connection The “Sun-Earth Connection” is the name given to a broad NASA program that includes studies of the Sun, the processes that link the Sun to the Earth, and the space environments and upper atmospheres of other solar system bodies. Another area of study characterizes the properties of the solar wind as it moves through the solar system. The overall goal of the program is to understand how and why the Sun varies and how the Earth and other planets respond to those variations. The Sun’s energy output varies on timescales from seconds to billions of years. This energy reaches the Earth in two forms: as electromagnetic radiation and charged atomic particles. The Earth responds to the Sun’s varying energy inputs in a number of ways. Growing evidence indicates that even small variations in the total energy emitted by the Sun can alter circulation in the Earth’s atmosphere and hence affect climate (e.g., the Maunder minimum in solar activity, which is associated with a little ice age in Europe in the 17th century). Ejections of mass from the corona, which are more frequent near the peak of the solar cycle, cause auroras and disturb the Earth’s ionosphere in such a way as to disrupt communications, disable power grids, and damage satellites and alter their orbits. In order to explore the effect of the Sun on the Earth, NASA is developing a series of missions that will characterize the solar energy output and the mechanisms that control it; explore the Earth’s space environment; compare the space environment of the Earth with that of other planets; and assess the impact of space weather on humanity. Many of these investigations will require access to archived data (see Box 1.2). A sampling of solar physics missions is listed in Table 1.2. Solar System Exploration NASA’s planetary exploration program is focused on answering fundamental questions about how planets form, why they are different from one another, and what conditions lead to the development of life. The last half of the 20th century was an extraordinary age of exploration and discovery. All of the planets in our solar system except Pluto have now been visited by NASA spacecraft. Each has been transformed from a remote astronomical object into a unique world, clearly distinct from all of the other objects in the solar system. Comparative planetology can provide real clues as to how the Earth itself and its habitability will be affected by changes in the total energy output of the Sun, climate change, increasing abundance of greenhouse gases, asteroid impacts, and so on. Planetary research has been one of the primary beneficiaries of the recent change in NASA philosophy to support a diverse set of missions of moderate scale. Flight opportunities have become more frequent; several comets and asteroids, in addition to the major planets, have now been visited and characterized; and the advent of modern detectors has greatly increased the volume of data from each mission. Table 1.3 presents a sampling of planetary missions.

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Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data BOX 1.2 Importance of Archives for Solar and Space Physics Following are examples of the role of NASA archives in advancing solar and space physics: The Solar and Heliospheric Observatory (SOHO) mission archive has provided nearly continuous data since 1996. This uniquely consistent archive of solar data has been mined to produce several new insights into solar phenomena. One example is the realization that coronal mass ejections (CMEs)—eruptions of gas that disrupt the flow of the solar wind and produce disturbances that strike the Earth causing electrical power outages, damaging communications satellites, and producing auroral displays—involve an unexpectedly large portion of the solar surface and that several spatially separate regions participate in the process. This observation implies that CMEs are the result of large-scale reorganization of the solar magnetic field, rather than localized events. Another example is the discovery of a subsurface flow of plasma toward the solar equator that exists only at the north pole and that advances and retreats as the solar activity cycle evolves. This is the first time that a flow asymmetric with respect to the equator has been discovered, and it may hold a key to the reversal in polarity of successive solar cycles. However, the flow has been observed so far for only a quarter of a single solar cycle and needs to be followed over multiple cycles before its role in solar activity can be characterized. In both of these examples, multiple archival data sets from different instruments were combined to clarify the nature of the phenomenon. Data from the Transition Region and Coronal Explorer (TRACE) mission have revealed that the solar atmosphere is threaded by an enormous number of very thin channels of high heat conductivity created by the solar magnetic field. These channels may be the key to unlocking the long-standing problem of coronal heating in solar and stellar physics. TRACE data are currently being used in new calculations of coronal thermodynamics. Such discoveries and applications are fostered by the availability of this continuous data record immediately and without restriction from the archive. By combining X-ray images, infrared images, and particle detector data, solar researchers have discovered that high-speed solar wind streams emanate primarily from the boundaries of coronal holes. Monitoring the evolving positions of coronal holes permits researchers to estimate when a solar wind gust will hit the Earth and disrupt telecommunications. The prediction of space weather as well as the exploration of the solar activity cycle is facilitated by the Solar Data Analysis Center, which provides “one-stop shopping” of three decades of data from past NASA solar missions and several major ground-based observatories, along with the tools to analyze them. SOURCE: Frank Hill, National Solar Observatory.

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Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data TABLE 1.2 Selected Solar and Space Physics Missions Mission Objective Current Missions Advanced Composition Explorer (ACE) Samples low-energy particles of solar origin and high-energy galactic particles, and provides near-real-time solar wind information. Fast Auroral Snapshot Explorer (FAST) Probes the physical processes that produce auroras. Genesis Collects particles of the solar wind and returns them to Earth. Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) Produces the first comprehensive global images of the plasma populations in the inner magnetosphere. Interplanetary Monitoring Platform 8 (IMP-8) Measures the magnetic fields, plasmas, and energetic charged particles of the Earth’s magnetotail and magnetosheath and of the near-Earth solar wind. International Solar Terrestrial Physics Global Geospace Science Program Polar (Polar) Images the aurora and measures the fluxes of charged particles and ions, magnetic and electric fields, and electromagnetic waves over the poles. Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX) Studies the composition of local interstellar matter and solar material and the transport of magnetospheric charged particles into the Earth’s atmosphere. Solar and Heliospheric Observatory (SOHO) Studies the internal structure of the Sun, its outer atmosphere, and the origin of the solar wind. Stardust Collects dust from a comet’s nucleus. Transition Region and Coronal Explorer (TRACE) Images the solar corona and transition region. Ulysses Explores interplanetary space at high solar latitudes. Voyager Interstellar Mission (VIM) Searches for the heliopause boundary, the outer limits of the Sun’s magnetic field, and the outward flow of the solar wind. International Solar Terrestrial Physics Global Geospace Science Program Wind (Wind) Samples the upstream interplanetary medium, a principal region of geospace where energy and momentum are transported and stored. Future Mission Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) Provide a new capability for stereoscopically imaging the magnetosphere. SOURCE: <http://spacescience.nasa.gov/missions/index.htm>.

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Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data TABLE 1.3 Selected U.S.-led Planetary Missions Mission Objective Current Missions Cassini Makes observations of Jupiter and its moons (atmospheric dynamics and composition, Jupiter’s magnetic environment, the interactions between Jupiter and its moons) on its way to Saturn. Galileo Studies Jupiter and its moons in more detail than any previous spacecraft. Mars Global Surveyor (MGS) Measures surface features, atmosphere, and magnetic properties of Mars. 2001 Mars Odyssey Maps the amount and distribution of chemical elements and minerals that make up the Martian surface. Future Missions Mars Exploration Rover Analyze rocks and soils for evidence of liquid water that may have been present in Mars’s past. Mars Express Explore the atmosphere, structure, and geology of Mars to search for subsurface water from orbit and deliver a lander to the Martian surface. Comet Nucleus Tour (CONTOUR) Image two comet nuclei, and collect and analyze dust to reveal the comet’s composition. SOURCE: <http://spacescience.nasa.gov/missions/index.htm>. EARTH SCIENCE ENTERPRISE Characterize, understand, and predict—these are the themes of NASA’s Earth Science Enterprise (ESE). The goal is “to develop a scientific understanding of the Earth system and its response to natural or human-induced changes to enable improved prediction capability for climate, weather, and natural hazards.”8 The research program is organized around a set of scientific questions aimed at understanding how the Earth is changing and the consequences of those changes for life on Earth.9 Some of the questions being addressed by the ESE program are as follows: How is the global Earth system changing? What are the primary causes of change in the Earth system? How does the Earth system respond to natural and human-induced changes? What are the consequences of change in the Earth system for human civilization? How well can we predict future changes in the Earth system?10 8   National Aeronautics and Space Administration, 2000, Exploring Our Home Planet: The Earth Science Enterprise Strategic Plan, May 25, 2000, draft. 9   National Aeronautics and Space Administration, 2000, Understanding Earth System Change: NASA’s Earth Science Enterprise Research Strategy for 2000–2010, January 2001, 46 pp.; National Research Council, 2000, Review of NASA’s Earth Science Enterprise Research Strategy for 2000–2010, National Research Council, Washington, D.C., 33 pp. 10   National Aeronautics and Space Administration, 2000, Understanding Earth System Change: NASA’s Earth Science Enterprise Research Strategy for 2000–2010, January 2001, 46 pp.

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Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data In order to answer these questions, the Earth Science Enterprise is currently conducting research in the following areas: Oceans and ice in the climate system; Biology and biogeochemistry of ecosystems and the global carbon cycle; Atmospheric chemistry, aerosols, and solar radiation; Global water cycle; and Solid Earth science. These research topics also address major subproblems of the U.S. Global Change Research Program11 to which a space-based observational system is uniquely capable of making a significant contribution.12 Current and upcoming ESE missions are listed in Table 1.4. Space-based data collected by the ESE address three classes of problems: (1) characterization of physical and biological processes, (2) monitoring status and changes, and (3) analysis of feedback mechanisms. “Characterizing and understanding a process” involves measurements to examine a specific process that operates in the Earth system, with the aim of developing physical models and model parameterizations. An example of this type of mission is the Tropical Rainfall Measurement Mission (TRMM),13 which measures the spatial and temporal variations in the tropical region (−35° to 35° latitude). The goals of this three-year mission are to study the frequency distributions of rainfall intensity and areal coverage and to relate the timing of heaviest rainfall to such factors as the nocturnal intensification of large mesoscale convective systems over the oceans and the diurnal intensification of orographically and sea-breeze-forced systems over land. TRMM data will potentially improve estimates of latent heating,14 which in turn will improve the prediction of rainfall events from global climate models. Recent results from TRMM, for example, show that windblown desert dust can choke rain clouds, cutting rainfall hundreds of miles away.15 Many of the instruments developed by the NASA ESE are used for systematic monitoring. An example of this class of instrument is the Total Ozone Mapping Spectrometer (TOMS).16 This class of instrument has been flown in four spacecraft with data extending back to November 1978 and has been used to monitor the amount of stratospheric ozone. A major result from the use of this and other instruments was the discovery of the growth of the Southern Hemisphere Ozone Hole,17 which led to the nearly worldwide phasing out of the use of the chlorofluoro- 11   The U.S. Global Change Research Program was established in 1989 to develop and coordinate a research program to understand, assess, predict, and respond to natural and human-induced global change. Nine federal agencies, including NASA, and the Executive Offices of the President participate in the program. See Subcommittee on Global Change Research, Our Changing Planet, The FY2002 U.S. Global Change Research Program, Washington, D.C., 74 pp. 12   National Research Council, 2000, Review of NASA’s Earth Science Enterprise Research Strategy for 2000– 2010, National Research Council, Washington, D.C., 33 pp. 13   See <http://trmm.gsfc.nasa.gov>. 14   Energy from the Sun is stored in the form of water vapor. Condensation of water vapor in clouds releases this latent heat, causing the atmosphere to warm locally. 15   See <http://www.gsfc.nasa.gov/gsfc/earth/dust/rainfall.htm>. 16   <http://toms.gsfc.nasa.gov/>. 17   The loss of ozone was first detected by the British Antarctic Survey, which was monitoring the atmosphere using a network of ground-based instruments. The TOMS data confirmed that the ozone loss was real and that it extended over most of the Antarctic continent. See G.Carver, 1988, The ozone hole tour, Part 1. The history behind the ozone hole, University of Cambridge, <http://www.atm.ch.cam.ac.uk/tour/part1.html>.

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Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data carbons (CFCs).18 The history of the total ozone measurements is composed of results from multiple instruments flown on different spacecraft; consequently, calibration between the results from these different instruments is critical to understanding the long-term evolution of total ozone. More importantly, new data are needed to determine if the mitigation steps (i.e., reducing the amount of CFCs released into the atmosphere) are effective. By their nature, long-term monitoring programs need to be able to relate measurements from different instruments, and the original data need to be available so that improved calibration and reduction algorithms can be applied. The final category of problem—analysis of feedback mechanisms—is the most challenging for any data system, because understanding cause and effect requires comparison of different data sets collected from different satellites with different types of instruments. One of the fundamental questions to be addressed in this class of problem is the role that clouds play in relation to the effects of increasing carbon dioxide and other greenhouse gases. Clouds both reflect sunlight (which cools the Earth) and trap heat in the same way as greenhouse gases (thus warming the Earth). Different types of clouds do more of one than the other. The net effect of clouds on climate change depends on which cloud types change, and whether they become more or less abundant, thicker or thinner, and higher or lower in altitude.19 Different instruments measure different characteristics of the clouds, and determination of the full impact of clouds requires that these measurements be merged. Understanding of the evolution of cloud-type cover, how cloud types are being affected by climate change, and how they in turn affect climate change requires access to long-time histories of space-based and ground data and the ability to apply new algorithms to original data to extract data relevant to cloud types. This type of synthesis of results is the most challenging for any data system, but it is also the area where the most significant results from the NASA ESE are likely to come. Many of the important science questions being addressed by NASA investigators require long-term, continuous measurements to detect and monitor environmental change. Consequently, data centers providing accessible, usable long-term data are essential in the earth sciences (see Box 1.3). 18   The breakdown of ozone by CFCs in the presence of high-frequency UV light was demonstrated in 1974 (M.J. Molina and F.S.Rowland, 1974, Stratospheric sink for chlorofluoromethanes: chlorine atom catalyzed destruction of ozone, Nature, v. 249, p. 810–812). International negotiations to reduce CFC levels began in 1983, but the Montreal Protocol was not signed until 1987, after the existence of the Antarctic ozone hole was confirmed and linked to CFCs. 19   See <http://www.giss.nasa.gov/research/intro/delgenio_03>.

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Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data TABLE 1.4 Selected ESE Missions Mission Objective Current Missions Active Cavity Radiometer Irradiance Monitor III (ACRIM III) Measures total solar irradiance from the Sun. Earth Radiation Budget Satellite (ERBS) Investigates how energy from the Sun is absorbed and reemitted by the Earth, and determines the effects of human activities on the Earth’s radiation balance. Landsat 7 Provides multispectral, moderate-resolution digital images of the Earth’s continental and coastal areas, with global coverage on a seasonal basis. SeaSTAR Measures bio-optical properties of the global ocean. Terra Provides global data on the state of the atmosphere, land, and oceans, as well as their interactions with solar radiation and with one another. Total Ozone Mapping Spectrometer Earth Probe (TOMS-EP) Provides daily global measurements of the total column ozone. Tropical Rainfall Measurement Mission (TRMM) Monitors tropical rainfall and the associated release of energy that helps to power global atmospheric circulation. Quick Scatterometer (QuikSCAT) Records sea-surface wind speed and direction for global climate research, weather forecasting, and storm warning. Future Missions Advanced Earth Observing Satellite (ADEOS)-II Measure near-surface wind velocity under all weather and cloud conditions over the Earth’s oceans. Aqua Measure clouds, precipitation, atmospheric temperature and moisture content, terrestrial snow, sea ice, and sea-surface temperature. Ice, Clouds, and Land Elevation Satellite (ICESat) Determine decadal variation of ice sheet thickness over Greenland and Antarctica, altitude and thickness of clouds, vegetation heights, land topography, and ocean surface and sea ice altimetry. Meteor Monitor the global distribution of aerosols, ozone, and other trace gases in the Earth’s atmosphere. Solar Radiation and Climate Experiment (SORCE) Provide total irradiance measurements (ultraviolet, extreme ultraviolet, and the visible to near infrared) required by climate studies. SOURCE: <http://gaia.hq.nasa.gov/ese_missions/default.cfm?transaction=Enter_ESE_Missions>.

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Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data BOX 1.3 Applications of Earth Science Archives Archived data have proven to be extremely important for investigations of changes in the Earth’s atmosphere, oceans, and land cover. Examples include: Global ocean surface topography has been measured by Ocean Topography Experiment (TOPEX)/Poseidon, a joint NASA-French Space Agency mission, since October 1992. The unprecedented accuracy (2 cm) and precision (4 mm) of the data allowed sea-level change in the Pacific to be monitored and predicted during the large 1997–1998 El Niño event.1 El Niño events disrupt the ocean-atmosphere system in the tropical Pacific, with global consequences for weather and climate. Analysis of TOPEX data has also augmented coastal tide gauge records, revealing a long-term global mean sea-level rise of 3.2 mm/yr, which can be completely explained by the thermal expansion of seawater. The relationship of the Pacific Decadal Oscillation to El Niño events or its effect on fisheries, coral bleaching, or ocean eddies has yet to be determined, owing to the relative shortness of the TOPEX data record. Such questions may be addressed as the current Jason-1 mission extends the record of sea-surface height another decade. Establishing the magnitude and causes of greenhouse warming requires access to accurate data over as long a period as possible. Harries and others recently used satellite interferometry data from NASA and Japan to compare the outgoing long-wave radiation spectra from the Earth in 1970 and 1997.2 They showed experimental evidence of “a significant increase in the Earth’s greenhouse effect that is consistent with concerns over radiative forcing of climate.” Their investigations were hampered by the poor quality of older data tapes, which had deteriorated over time.3 Considerable effort was required to rescue the data and make them usable, illustrating the importance of routine migration of data to new media and working with archived data to ensure their long-term scientific value. 1   C.Cabanes, A.Cazenave, and C. Le Provost, 2001, Sea level changes from TOPEX/Poseidon altimetry for 1993– 1999, and warming of the southern oceans, Geophysical Research Letters, v. 28, p. 9–12. 2   J.E.Harries, H.E.Brindley, P.J.Sagoo, and R.J.Bantges, 2001, Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997, Nature, v. 410, p. 355–357. 3   Richard Goody, Professor Emeritus, Harvard University, personal communication to J.Purdom, fall 2001. THE CHANGING PARADIGM FOR NASA With the adoption of the scientific goals of the Earth Science and Space Science Enterprises, NASA can no longer be viewed primarily as a technology-demonstration agency. Instead, NASA has defined itself as a knowledge-generating agency, with missions at the front end of the information pipeline. NASA data are a national resource; the stewardship and exploitation of NASA data are necessarily a national responsibility. The care of the data, including the tasks of archiving and distribution, must be accomplished so as to maximize knowledge enhancement, scientific impact, and discovery potential. The chapters following describe and evaluate the strategies adopted by NASA to date and make recommendations to enhance the usefulness and accessibility of the growing databases obtained from NASA missions.