Mission to planet earth: Earth observing system

Palaeogeography, Palaeoclimatology, Palaeoecology (Global and Planetary Change Section), 98 (1992) 3-8 Elsevier Science Publishers B.V., Amsterdam

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Mission to Planet Earth: Earth Observing System Ghassem Asrar, Shelby G. Tilford and Dixon M. Butler Earth Science and Applications Division, Office of Space Science and Applications, National Aeronautics and Space Administration, Washington, DC 20546, USA (Received June 19, 1992)

ABSTRACT Asrar, G., Tilford, S.G. and Butler, D..M., 1992. Mission to Planet Earth: Earth Observing System. Palaeogeogr., Palaeoclimatol., Palaeoecol. (Global Planet. Change Sect.), 98: 3-8. Earth Observing System (EOS) is one of the components of the Mission to Planet Earth (MTPE) concept for an international Earth science program to provide the observations, understanding and modeling capabilities needed to assess the impact of natural events and human induced activities on the Earth's environment. MTPE is envisioned to have both the space-based and ground-based observational capabilities, along with the necessary data and information system(s) to accommodate the acquisition, archive and distribution of the data and information acquired about the Earth system. The knowledge gained through this multidisciplinary and international scientific partnership will help increase our understanding of the functioning of the Earth as a coupled system, a prerequisite to informed management of the planet's resources and to the preservation of the global environment.

Introduction Scientific research shows that the Earth has changed over time and continues to change. Irrefutable evidence indicates that human activity has altered the nature of the Earth by changing the landscape over large portions of the Earth's surface and by altering the composition of the global atmosphere. There are now strong indications that the rate of change is accelerating as a result of human activity. In the quest for improved quality of life, humanity has become a dominant force on the planet, building upon, reshaping, and modifying nature, sometimes in unintended ways. The need for the mission In the next century, Planet Earth faces the prospect of accelerated environmental change, including climate warming, rising sea level, deforestation, desertification,

Correspondence to: G. Asrar, Earth Observing System, Earth Science and Applications Division, Office of Space Science and Applications, National Aeronautics and Space Administration, Washington, DC 20546, USA.

ozone depletion, acid rain, and reduction in biodiversity. Such changes will have a profound impact on all nations, but many important scientific questions remain unanswered. For example, while most scientists agree that global warming is likely, its magnitude and timing, especially at the regional level, are quite uncertain. Additional information on the rate, causes, and effects of global change is essential. NASA is working with the national and international scientific community to establish sound scientific basis for addressing these issues through the coordinated research efforts under the US Global Change Research Program (GCRP), the Committee on Earth and Environmental Sciences (CEES), International Geosphere-Biosphere Program (IGBP), and the World Climate Research Program (WCRP). Carbon dioxide, methane, nitrous oxide, and other gases trap heat emitted from the Earth's surface, thus warming the global atmosphere. Long-term measurements over the past several decades have documented a rapid rise in concentrations of these greenhouse gases, but the long-term trend of global temperatures is not yet predictable. Changes in other variables, such as global cloudiness, concentration of atmospheric dust particles, and ocean circulation patterns also have an impact on global temperature. However, the existing

0921-8181/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved

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systems for global monitoring are not adequate, nor is the modeling of these interactive processes sufficiently accurate, to predict the magnitude and timing of change with reasonable accuracy. Climate studies predict that tropical deforestation will cause a decrease in rainfall and an increase in temperature. In addition to their impact on atmospheric heat and humidity, forests also exchange trace gases between soil and atmosphere, and nourish the fcrtility of the land. They support a diversity of life and are a major sink for atmospheric carbon dioxide. The biosphere and atmosphere are coupled through the hydrologic and biogeochemical cycles. Changing the composition of the land biosphere will have a direct impact on the atmosphere, rivers, and transport of nutrients to oceans, and such change continues to take place every day, yet their long-term effect is unknown. Once again, at present, scientists cannot predict satisfactorily the coupling between biosphere and atmosphere and the impact of change in composition of terrestrial ecosystems on the global climate. Research can play a critical role in increasing our understanding of change and providing guidance for policymakers. The study of ozone levels by the Upper Atmosphere Research Program is a primary example of Earth science research providing a clear picture of human-induced global change. In the 1970s, scientists first proposed the chemical processes b~¢ which human-made chlofluorocarbons (CFCs) deplete stratospheric ozone. Only after a long-term program of in-situ and space-based research and continuous global monitoring did the international scientific community reach a consensus on global ozone depletion. The evidence and understanding gained from this research led to the Montreal Protocol for worldwide reduction in the production of CFCs in the 1990s. Mission overview

MTPE is a NASA-initiated concept that uses spaceand ground-based measurement systems to provide the scientific basis for understanding global change. NASA's contributions to MTPE include ongoing and near-term satellite missions, new programs under development, planned future programs, and a continuing basic research program focused on process studies and modeling and satellite data analysis. Together, the space-based components of the mission will provide over time a constellation of satellites that will monitor the Earth from space. But, space-based research and monitoring are not sufficient; a comprehensive data and information system, and a commum~y of scientists performing research with the data acquired and conducting extensive ground-based research campaigns are

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all important components. More than any other factor, the commitment to make Earth science data easily available to the research community is critical for mission success. Following is a brief description of the various elements of the overall mission. Mission to Planet Earth flight programs

Platforms stationed in a variety of orbits form the space component of MTPE. There is no single orbit that permits the gathering of complete information on Earth processes. For example, the medium-inclination orbit of the recently launched Upper Atmosphere Research Satellite (UARS) was chosen specifically because of the program's focus on the processes influencing ozone depletion. The EOS satellites under development will fly in polar orbit to provide global coverage of the atmosphere and Earth surface. Some of the smaller Earth Probes satellites with specialized instrumentation will be flown in lower-inclination orbits for investigations that cannot be accomplished otherwise. Early in the next century, new geostationary satellites will provide continuous monitoring of high-temporalresolution processes on a near global basis. Each flight program has a dedicated science team, and the data from each will be made available to the wider scientific community on a full and open basis.

Currently operating • The Total Ozone Mapping Spectrometer (TOMS)/Meteor-3, launched during August 1991, is a US instrument to measure the concentration of ozone in the upper atmosphere launched on a Soviet meteorological satellite. Measurements from this instrument will supplement and continue the measurements from the TOMS instrument still operating on the NIMBUS-7 satellite launched in 1978. • UARS was launched in September 1991, carrying instruments to study the distribution of stratospheric ozone and other trace gases to further our understanding of the interaction among dynamic, radiative and chemical processes in the Earth's stratosphere. • The Earth Radiation Budget Experiment (ERBE), a program to investigate globally the heating and cooling of the atmosphere, is using instruments launched in 1984 and 1985 on various satellites in different orbits. • In addition to these dedicated research missions, NASA scientists conduct research using data from operational satellites operated by the US National Oceanic and Atmospheric Administration (NOAA), its counterpart environmental monitoring agencies around

MISSION T O P L A N E T E A R T H : E A R T H O B S E R V I N G SYSTEM

the world, the US Department of Defense (DoD), and the Landsat.

Under development • T O P E X / P o s e i d o n (with France) currently scheduled for launch in mid-1992, is an ocean topography experiment to study ocean circulation and its influence on the global environment. • The Shuttle Imaging Radar-C (SIR-C), Scanning Solar Backscatter Ultra Violet Experiment (SSBUVE), Lidar In-space Technology Experiment (LITE), and the Atmospheric Laboratory for Applications and Science (ATLAS) are advanced spaceborne instrument development campaigns scheduled for deployment on multiple NASA space shuttle missions in 1992 and beyond. • Radarsat is a Canadian program for which N A S A is supplying a launch in 1995. The satellite will carry a synthetic aperture radar instrument particularly valuable for study of the Earth's polar regions. The Earth Probes Program, composed of specialized satellites that address specific Earth science needs, is a major component of MTPE. They will make observations that cannot be accomplished from polar orbit. The Earth Probes Program includes the launch of a satellite every 2-3 years. • The Sea Wide Field Sensor (SeaWiFS), an ocean color sensor to study ocean productivity and interactions between the ocean ecosystems and the atmosphere, will launch in 1993. • Additional copies of the TOMS instruments will fly on a N A S A explorer-class satellite in 1993 and on J a p a n ' s A d v a n c e d Earth Observation Satellite (ADEOS) in 1996 to ensure the continuity of vital global ozone measurements. • The N A S A Scatterometer an instrument which will study the ocean's surface to determine wind patterns and air-sea interaction, will also be launched on Japan's A D E O S satellite in 1996. • The Tropical Rainfall Measurement Mission (TRMM) is a joint program with Japan, scheduled for launch in 1997. TRMM will make extensive measurements of precipitation in tropical regions, the heat engine for global climate, which cannot be time-sampled adequately from polar orbit. The centerpiece of NASA's contributions to MTPE is the Earth Observing System (EOS), a series of polar orbiting platforms for long-term global observations of the Earth's land biosphere, geosphere, atmosphere, and oceans, which combined with polar-orbiting and mid-inclination platforms from Europe and Japan will form a comprehensive international system. Starting

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with the N A S A and European Space Agency (ESA), polar platform programs will establish an internationally Earth observing capability that will operate for at least 15 years. Scientists will be able to obtain information at many levels of detail, covering all of the major Earth system processes. The program's investigations will involve development and operation of remote-sensing instruments and the conduct of interdisciplinary investigations using data from these instruments. EOS science objectives are focused on advancing knowledge on each of the fundamental physical, chemical, and biological phenomena that govern and integrate the Earth system, including: • Hydrologic processes, that govern the interactions of land and ocean surfaces with atmosphere through transport of heat, mass and momentum. • Biogeochemical processes, that contribute to the formation/dissipation and transport of trace gases and aerosols, and their global distribution. • Climatological processes, that control formation/dissipation of clouds and their interaction with solar radiation. • Ecological processes, that are effected a n d / o r will affect the global change, and their response to such changes through adaptation. • Geophysical processes, that have shaped or continue to modify the surface of the Earth through tectonics, volcanism and melting of glaciers and sea ice. The following papers in this and the companion special issue discuss in depth the scientific questions, required observations and modeling capabilities in each of these areas. The challenge is to integrate the knowledge gained through these efforts such that allows understanding the functioning of the Earth as a system.

Future plans The Geostationary Platform Program calls for a constellation of five satellites that will make continuous observations over the same geographic areas to permit intensive study of both daily variability and changes over longer time periods. Much as geostationary weather satellites track storm systems today, these platforms will monitor dynamic short-term phenomena that cannot be observed from polar or low-inclination orbits. The science objectives for the Geostationary Platforms focus on increasing understanding of short-term processes necessary to build adequate physical and dynamical modeling and parametrization in global Earth system models. Geostationary Platforms will require the design and development of new or improved advanced technology. NASA plans to proceed with definition activities, lead-

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ing to the launch of the first Geostationary Platform after the turn of the century. Future geostationary research satellites may assist with the planning and development of the next generation of geosyncbronous weather satellites. Preliminary technical discussions on establishing this global research capability in geostationary orbit have been held with European and Japanese agencies. Additional Earth Probes are also p l a n n e d - - a continuing series of small, less expensive missions for highly focused studies of specific global Earth processes. Possible missions include: • Applications and Research Involving Space Technologies Observing The Earth's field from Low Earth orbiting Satellite (ARISTOTELES): A possible joint mission with ESA to provide high-resolution, low-altitude measurements of the Earth's gravitational field. a Magnetic Field Experiment ( M F E ) / M A G NOLIA: A possible joint mission with France to make detailed measurements of the Earth's magnetic field and its changes to understand internal motions in the Earth and the origins of long-term changes on the Earth's surface. • Global Topography Mission (GTM): A possible joint mission with Italy to obtain complete, high resolution digital elevation maps of the Earth's continents and ice caps.

Data and information system The EOS Data and Information System (EOSDIS) will serve as NASA's primary Earth science data system until well into the next century. As such, it will link all the N A S A space-based research elements of Mission to Planet Earth. The EOSDIS will facilitate ready access to the program's information on a timely and non-discriminatory basis. EOSDIS will provide interfaces to interagency and international networks and systems that link it to the entire global change community. Meeting these objectives has been an integral part of EOSDIS planning. EOSDIS is being designed through competitive studies by industry with substantial contributions from the scientific community. EOSDIS will provide computers for NASA-sponsored EOS scientists, ensuring that the scientists complete and deliver to NASA useful procedures for processing instrument measurements into meaningful information. The system will be designed and implemented in an evolutionary fashion, thus allowing for changes in the data processing as more is understood about the instruments and about how the Earth works as a system. The design will include excess capacity so that old data can be reprocessed without creating a backlog of new data.

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NASA will be responsible for designing and operating EOSDIS to produce standard products. NASA will archive the data in the short term (1-3 years), and then will transfer some of the responsibility for long-term data management to partner agencies. For example, the land surface data from EOS will be processed and archived in Sioux Falls, South Dakota, at the US Geological Survey (USGS) Earth Resource Observation Data Center, which now houses the US Government's archive of Landsat data. NOAA will manage the long-term archive of a portion of the oceanic and atmospheric data in a similar arrangement. NASA will tie EOSDIS to a larger Global Change Data and Information System (GCDIS) through the Interagency Data Working Group within the United States. Every Government agency with data of interest to the global change community is participating in the design of this cooperative effort. Building on existing and planned agency systems, the GCDIS will connect each agency's catalog systems, quality assurance methods, procedures, and common services, and provide a comprehensive directory of existing data and information products. NASA is working with NOAA and other international satellite operators and data processors to establish common approaches for data formats, directories, sensor calibration, documentation, network connections, and other key issues. Many agreements are in place for data exchange, and negotiation of additional agreements is underway. This process of agreeing on standards and availability is critical in enabling scientists to exploit the wealth of new information that will be available to them. Each space agency participating in MTPE will provide research access to the data on easy, affordable terms as a condition for participation. The commitments will be formalized in international agreements currently under discussion. U.S. government policy states that data will be provided to global change researchers for the marginal cost of fulfilling the specific user request. Current plans call for the subset of data desired by the operational environmental monitoring community to be distributed without a marginal cost. Each participating nation will have thc right to define terms for access to data from its sensors for commercial use. N A S A will encourage all nations to contribute their research efforts to the collective endeavor, including nations that are not spacefaring, as a quid pro quo for low-cost access to MTPE data.

Interdisciplinary research efforts Only by studying the Earth as an integrated system can scientists begin to understand the complex relations among its unique phenomena. NASA has always

MISSION TO PLANET EARTH: EARTH OBSERVING SYSTEM

funded research in specific Earth science disciplines that contribute to a detailed understanding of individual processes. One of the objectives of MTPE is to forge new alliances among scientific disciplines, to require scientists to enter into truly interdisciplinary teams that address global issues. When viewing the Earth, scientific instruments aboard spacecraft are not limited to making observations of value to only one specific discipline. These instruments view an ensemble of processes that typically require teams of specialists to understand the elements and their interactions. Physical, chemical, and biological processes connect the oceans, continents, atmosphere, and biosphere in a complex way. A complete understanding of these elements requires that they be studied not only in isolation but also in concert with other Earth system processes. The EOS program is an excellent example of the kind of scientific cooperation envisioned for MTPE. NASA selected 29 teams of researchers for EOS studies specifically to investigate interdisciplinary questions. The goal of each study is to develop an accurate understanding of one or more of the key global processes. Based on this understanding, the studies will develop quantitative models of the processes, test this knowledge against in situ and space-based measurements, and provide a means for assessing the future course of these processes. The importance of the science component of MTPE cannot be overstated. To achieve its goals, MTPE must both obtain the long-term data needed by scientists, and make it available to all users. The program will produce global maps of surface temperature, precipitation, soil moisture, clouds, land-surface cover types, atmospheric ozone, ocean color and other parameters and processes required to understand the state of the Earth, and to detect any patterns of change. We envision active participation of national and international Earth scientists in MTPE, including the next generation of Earth scientists, many of whom will be trained and supported under NASA Earth science education programs. Education

MTPE meets the challenge of fostering a new generation of Earth system scientists by sponsoring a wide range of education and training programs. NASA has established the Earth System Science Education Program to enhance awareness, interest and knowledge of Earth system science by teachers and students (preschool-graduate), and the public. This goal is accomplished through developing projects that: empower teachers with creative approaches to teaching Earth

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system science within existing curriculum; augment existing student experiences in Earth system sciences; provide financial support and incentives for undergraduate and graduate student research and training in Earth System Science; and stimulate cooperative activities with universities and other US agencies participating in the Global Change Research Program. For example, the NASA Graduate Student Fellowship in Global Change Research was established in 1990 to support graduate students pursuing PhD degrees in the Earth sciences. The program was formed to train the next generation of scientists and engineers to help analyze, interpret and manage the wealth of data and information generated during the EOS era, in support of the U.S. GCRP. The program was envisioned to scale up to fund 150 graduate students prior to the launch of the first EOS spacecraft, and to remain at that level during the life of the EOS mission. Due to overwhelming response over its first 3 years, the program has already achieved more than 90% of this commitment, firmly ensconcing itself in the EOS program by providing the necessary talent to further the Earth system science objectives. International coordination

Leaders of all nations require an accurate assessment of global change issues. Developing an international scientific consensus on the causes and course of future global change will require a comprehensive and well-coordinated program of scientific research and global observations. To meet this challenge, researchers from around the world must work together to increase their understanding of how the Earth works as a system, to enhance the prediction and management of change. Space agencies worldwide are addressing the general technical barriers to increased international coordination and data exchange. The primary forum for multilateral international coordination of MTPE is the Committee on Earth Observations Satellites (CEOS). The membership of CEOS has recently expanded, and the group is concentrating on coordinating the requirements of international science programs such as IGBP and WCRP with the observation plans of space agencies. CEOS Working Group on Data activities include efforts to agree on common data formats for similar sensors flying on different satellites, intercalibration of data from different sensors, increased coordination of instrument validation, and development of international data directories. The CEOS Working Group on Calibration and Validation is engaged in coordination of planning for instrument calibration and validation campaigns.

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NASA is cooperating with space agencies in France, the United Kingdom, Canada, Germany, Italy and the Commonwealth of Independent States on early flight programs within MTPE, and with Japan in several of the Earth Probe flight programs. Selection of instruments for the EOS and its associated programs has been coordinated between the partner agencies (from Japan, Europe, and Canada) to ensure a proper balance of capabilities to meet overall scientific objectives. These partners are now working on mission management, common instrument interfaces, and data policy arrangements, among other issues, to ensure that the international suite of observations is well-planned and mutually supportive. The degree of coordination already achieved offers an excellent foundation for expanded international participation in MTPE.

Conclusions

MTPE and EOS offer the inhabitant of planet Earth to gain a new perspective of its functioning through coordinated and long-term space-based and in situ observations, and a program of basic research through fostering interdisciplinary research and Earth System Science approach. MTPE is a US Presidential initiative which has been supported by the Congress by granting NASA the new start in 1990. During the early EOS period (i.e. from now until first EOS launch in 1998), NASA is sponsoring several activities to provide easy access to the existing data from the Earth observing research and operational satellites under the "pathfinder" projects. The planned national and international space-based observations will assure the continuity and improved spatial, spectral and temporal resolution of measurements currently provided plus additional and new measurement capabilities. These new instruments will also provide enhanced accuracy and precision measurement capabilities dictated by the Global Change Research Program, that are not met by current Earth observing satellites.

The Earth Probes are an essential component of MTPE. They will assure the continuity of some measurements (e.g. TOMS), and also new measurement capabilities (e.g.TRMM), prior to the launch of the EOS and ESA polar platforms. The ARISTOTELES and GTM missions will provide complementary data to those planned as part of polar orbiting Earth observatories beyond 2000. To foster the Earth System Science concept broadly, new alliances should be forged among the disparate Earth science disciplines to join efforts in an interdisciplinary mode to address global change issues. Education and training of the next generation of Earth scientists who will support interdisciplinary research in the context of Earth System Science is a major challenge facing the national and international educational institutions. This can be accomplished through establishing educational programs that empower teachers with creative approaches to teach Earth System Science at all levels (elementary to graduate), augmenting the existing curriculum and developing new ones as needed, providing support for qualified students pursuing research and training in Earth System Science, and stimulating cooperative research and training between academic institutions and US Federal agencies. The papers presented in this and a following issue of Global and Planetary Change represent the scientific issues/ requirements identified by the scientists participating in the EOS program under NASA sponsorship. They represent the current understanding and knowledge based on limited observation capabilities which exist today. Over the next several years, our observational and data processing capabilities, and scientific understanding of the issues identified will undoubtedly improve. This improved understanding will provide the necessary knowledge for sound policy decisions on how to preserve and protect the Earth and its environment through sound management practices. With this, we also hope to refine and improve the current measurement and modeling capabilities needed through MTPE and EOS in support of the US Global Change Research Program.