FROM SATELLITE OBSERVATIONS TO EARTH INFORMATION

The program of observations described on the preceding pages is designed to be effective in its use of resources, resilient to evolving constraints, and open to embracing new opportunities as they arise. The recommended missions can provide a wealth of new and urgently needed data on the Earth system. However, these observations—as important as they are —will prove useful only if they can be effectively analyzed, interpreted, and applied. The missions are one part of a larger program needed to translate raw observations of Earth into useful information. To realize the potential offered by these missions, resources must be focused in the following four areas: ensuring sustained observations for operations, research, and monitoring; obtaining complementary non-space-based observations; turning observations into knowledge and information; and sustaining the knowledge and information system.

THREE TYPES OF OBSERVING

  • Exploratory observations are designed mainly to advance scientific understanding. They can lead to unexpected discoveries, test hypotheses, and validate models. They may also reveal changes in parts of the Earth system that are critical to our well-being.

  • Operational observations are those designed to serve routine functions such as day-to-day weather prediction. These observations generally must be collected and processed in real time. Sometimes data from exploratory observations are shown to have a large positive impact on weather forecasts and become critical to operational systems.

  • Sustained observations of certain key variables, such as sea surface temperature and sea level, atmospheric temperature, and solar radiation, are needed to clarify the long-term implications of a change in the Earth system or to uncover slowly evolving dynamics.



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frOm Satellite ObServatiOnS tO earth infOrmatiOn t he program of observations described on the preceding pages is designed to be effective in its use of resources, resilient to evolv- ing constraints, and open to embracing new opportunities as they arise. the recommended missions can provide a wealth of new and urgently needed data on the earth system. however, these observations—as important as they are —will prove useful only if they can be effectively analyzed, interpreted, and applied. the missions are one part of a larger program needed to translate raw observations of earth into useful infor- mation. to realize the potential offer- ed by these missions, resources must be focused in the following four areas: ensuring sustained observations for oper- ations, research, and monitoring; obtaining complementary non-space-based observa- tions; turning observations into knowledge and information; and sustaining the knowledge and information system. THREE TYPES OF OBSERVING • exploratory observations are designed mainly to advance scientific understanding. they can lead to unexpected discoveries, test hypotheses, and validate models. they may also reveal changes in parts of the earth system that are critical to our well-being. • operational observations are those designed to serve routine functions such as day-to-day weather prediction. these observations generally must be collected and processed in real time. sometimes data from exploratory observations are shown to have a large positive impact on weather forecasts and become critical to operational systems. • sustained observations of certain key variables, such as sea surface temperature and sea level, atmospheric temperature, and solar radiation, are needed to clarify the long-term implications of a change in the earth system or to uncover slowly evolving dynamics. 

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earth Science and applicatiOnS frOm Space  ENSURING SUSTAINED OBSERVATIONS FOR OPERATIONS, RESEARCH, AND MONITORING observational systems can be classified into three overlapping categories: exploratory, opera- tional, and sustained (see box on page 27). sustained measurements are those that must be made over many years in order to distinguish short-term variability from long-term trends. these obser- vations become part of the climate data record. they are also necessary for research on important natural oscillations in the climate system that have periods of decades or longer. one reason for the complexity in coordinating space-based earth remote sensing is that observations frequently serve multiple goals at the same time. indeed, exploratory missions often produce innovative observations that can be employed in an operational setting and also contrib- ute to a long-term program of sustained observation. the challenge of transitioning missions from exploratory to operational status is well recognized and long studied, but progress to date has been mixed. moreover, operational sensors do not always provide the type of sustained observations needed to accurately track and analyze climate change. for instance, major uncertainties in the long-term trend of upper-air temperatures exist in part because of the attempt to create climate records from what are essentially weather-focused oper- ational observations. the committee is concerned that the nation’s institutions involved in civil space activities are not adequately prepared to mount a coordinated observing strategy and meet society’s long- term needs for sustained observa- tions and earth information. these institutions have responsibilities that are often mismatched with authorities and resources; man- dates inconsistent with their charters; budgets that do not address emerging needs; and shared responsibilities hampered by a lack of mechanisms for coop- eration. these fundamental issues need to be addressed through high- level federal policy. the committee recommends that the office of science and technology Policy, working with partners in agencies and academia, develop and implement a plan for achieving and sustaining global earth obser- vations. further, noaa, working with its partners, should create a data and information system to ensure the production, distribution, and stewardship of high-accu- racy climate records.

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earth Science and applicatiOnS frOm Space  OBTAINING COMPLEMENTARY NON-SPACE-BASED OBSERVATIONS observations from the vantage point of space can provide an economical and global view of many earth system phenomena and processes. however, the laws of physics impose funda- mental limitations and require trade-offs in the sensitivity and spatial and temporal resolution that space-based instruments can achieve. thus, space observations cannot always provide all of the data needed to understand key physical, chemical, and biological processes. in situ instruments (sensors on land, at sea, and aboard aircraft that measure conditions at their immediate locations) remain critical for calibrating and validating satellite observations and for gathering data with levels of accuracy, precision, and resolution that are unavailable from space-based sensors. nationally and globally, the core in situ weather observations made for more than 50 years have come from surface stations and radiosondes (balloon-borne instrument packages). today, however, the number of radiosonde observations is declining in many parts of the world, although satellite data partially compensate for this loss. the surface-based network of U.s. weather observing stations serves the need for weather pre- diction, but it is inadequate for climate monitoring and re- search. to remedy this situation, noaa is developing the U.s. Climate Reference network, a group of about 100 observing stations that will provide homoge- neous long-term observations of temperature and precipitation, helping to place observed trends into historical perspective. similar surface-based networks exist for stream- flow monitoring, seismic measurements, and other purposes; these need to be maintained and enhanced. aircraft are another source of routine weather observations and an essential tool in earth system re- search. many satellite-borne sen- sors for earth observation were conceived for and tested on aircraft, and airborne field campaigns are a vital training ground for graduate students. Yet nasa’s airborne re- search facilities are in significant jeopardy. the limits on aircraft use are growing, while support for stag- ing field campaigns and developing instruments has decreased and the level of technical infrastructure for airborne mis- sions has declined. the transition of airborne programs at nasa and noaa from conventional aircraft to unpiloted aerial vehicles (UaVs) presents opportuni- ties as well as risks. UaVs provide increased range and flight time and the ability to penetrate environments that

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earth Science and applicatiOnS frOm Space 0 might be too hazardous for piloted aircraft. however, issues of cost, reliability, software, and proxim- ity to urban areas have limited the use of UaVs to demonstration missions. for now, conventional aircraft remain more reliable and more cost-effective for earth sensing, and agencies need to ensure an appropriate balance between these two types of platforms. Understanding the interaction between human activities and the natural environment is of grow- ing interest. space-borne and in situ observations greatly enable this understanding, but for maximum usefulness they need to be coordinated with additional information about urban areas and other human-modified landscapes. much of this information currently falls within the domain of social sci- entists, economists, geographers, urban planners, and others not traditionally part of the earth science community. increased collaboration with these groups is essential. TURNING OBSERVATIONS INTO KNOWLEDGE AND INFORMATION a central theme of the decadal survey report is the utility of space-based observations of the planet for addressing important societal needs. achieving benefits for society will require the develop- ment of an integrated process that transforms observations into useful information. We also need to improve our ability to assimilate data from multiple observations and sensors, while addressing well- known challenges of data and information management. to provide a more direct route from space-based observation to societal benefits requires that social scientists be more involved throughout the entire life cycle of a given mission. Closer ties between physical and social scientists can also help make the resulting mission data more readily available to a broader range of users through improved access, education, and training. as discussed in several recent national Research Council reports, an increasing challenge is to manage and process the flow of earth-system data gathered from the above systems. every mission must have a plan for processing and archiving data and making the data easily accessible at little or no cost to users. Research and analysis efforts such as those at nasa need to be maintained and strengthened. Likewise, support for modeling, computing, and data assimilation is essential in order to maximize the value of our investment in observing systems. nasa should enhance its Research and analysis (R&a) program to provide this crucial scientific underpinning, ensuring adequate support for R&a as well as operations and data analysis associated with the recommended missions. Commercial entities are also providing a rapidly growing array of earth information services, many of them free. While these are not expected to replace government systems, they can serve as a valu- able adjunct. the committee recommends that teams of experts be formed to combine and assimilate data from both public and private sources. SUSTAINING THE KNOWLEDGE AND INFORMATION SYSTEM a successful long-term plan for monitoring earth from space must be durable enough to withstand changes in leadership, variations in funding, advances and slowdowns in technology, and other hard-to- predict factors. such a plan should incorporate mechanisms for adapting to evolving constraints as needed, and it should build the next generation of leaders through committed education and training. to ensure long-term programmatic stability, the decadal survey report encourages the formation of an independent, community-based advisory body that regularly reviews the status of space-based earth observing systems as a whole, with an eye to potential problems as well as opportunities. such a group will need to provide advice consistent with evolving plans for both domestic and international programs. it should also seek opportunities for efficiencies that come from collaboration and data sharing.

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earth Science and applicatiOnS frOm Space  to assist with issues that inevitably arise as programs are repriori- tized and adjusted and to help guide programmatic decisions, com- mittee members developed the following strategies and rules: • Leverage international efforts. Restructure or defer mis- sions that are largely duplicated by other nations; when appropriate, offer cost-effective additions to interna- tional missions to extend their value. • Manage technology risk. sequence missions accord- ing to technological readiness and budgetary risk; invest early in efforts to meet important technologi- cal challenges. • Develop a mechanism for responding to budget pressures and shortfalls. implement an independent review process to ensure that larger objectives are considered; delay or cancel missions if cost overruns grow large; when missions must be dropped, elimi- nate some within each theme area (see box on page 6), rather than dropping entire themes; if budget shortfalls are large, seek community input and reevaluate the observing program as a whole rather than in a piece- meal fashion. ensuring balance is an important high-level principle essen- tial to maintaining the integrity of the overall plan for earth sensing from space as priorities change and programs are adjusted. Balance should be sought across: • Scientific disciplines, so that the range of expertise needed for interdisciplinary earth systems science is available and break- throughs in specific areas are nourished; • Mission sizes, to allow for participation at multiple levels of the scientific community and to balance long-term pursuits with a capability for timely response to emerging ideas; • Technology maturity, so that roadblocks to mission progress are kept to a minimum; • Observations, analysis, and modeling, so that the appropriate tools are available to analyze and understand new data as they become available; and • Stability and adaptability, so that new societal needs can be met while long-term programs of value are protected. as our nation’s approach to observing earth from space is revitalized, it is exceedingly impor- tant that future scientists obtain the education and training they need to interpret new observations and turn them into knowledge that benefits society. such training can be provided through sym- posia and workshops for smaller, more specialized communities. Larger audiences can be accom- modated through computer-aided distance learning. to ensure the wide and effective use of earth observation data, opportunities for education and outreach should be emphasized early on so that both the science and the user communities are ready when new data become available. educators will thus also be able to integrate information on new missions and their benefits into curricula for elementary-school through university levels. such efforts will expand the science literacy of future scientists, teachers, and the public as a whole.

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earth Science and applicatiOnS frOm Space  KEY ELEMENTS OF THE MISSIONS ORBIT ALTITUDES Low Earth orbit (LEO): an orbit typically between 300 and 2,000 kilometers above earth Sun-synchronous orbit (SSO): an orbit structured so that the satellite passes over a given point on earth at the same time each day Medium Earth orbit (MEO): an orbit in the range between Leo and Geo, used by the Global Positioning system (GPs) and other navigational and communications satellites Geosynchronous Earth orbit (GEO): an orbit that is useful for applications that require a satellite to appear stationary with respect to a fixed point on the rotating earth. to achieve such an orbit, an object must be placed into a circular orbit in a plane aligned with earth’s equator, and at an altitude such that the orbital period of the satellite is exactly equal to earth’s period of rotation (approximately 24 hours). the altitude for geostationary orbit is approximately 36,000 kilome- ters above sea level. WAVELENGTHS Microwave: 1 millimeter to 30 centimeters; typical wavelengths used by radars, scatterometers, and radiometers; classified into wavelength ranges identified by letter (e.g., x-band or K-band) Infrared (IR): 750 nanometers to 1 millimeter; useful in detecting clouds, ocean eddies, and other earth system features, especially those involving water or water vapor Visible (400 to 700 nanometers) and ultraviolet (1 to 400 nanometers): useful for space-borne remote sensing of molecular species in earth’s troposphere and stratosphere INSTRUMENT TYPES Active (sends signals and receives returns) Radar (radio detection and ranging): detects and characterizes objects by transmitting pulses of radiation, typically in the microwave range, and analyzing the portion of the signal that is reflected and returned to the sensor Lidar (light detection and ranging): similar to radar, but using laser light instead of radio signals Scatterometer: specialized radar used mostly to determine wind speed and direction near the ocean surface, but can also be used over land to study ice and vegetation Altimeter: specialized radar or lidar that measures the height of the land or sea surface Passive (receives signals from the Sun, the Earth system, or other satellites) Radiometer: measures the intensity of energy radiated by an object at a given wavelength, typi- cally at infrared or microwave wavelengths Limb sounder: observes earth’s limb (the horizon from space) and measures radiation emitted by or passing through various heights of earth’s atmosphere GPS receiver: receives radio waves emitted from GPs satellites; can be used to analyze varia- tions in signal speed and infer atmospheric properties (through a technique called radio occulta- tion), and to determine position Spectrometer: measures light received in terms of the intensity at constituent wavelengths to determine chemical makeup, temperature profiles, and other atmospheric properties Interferometer: combines signals from two or more wavelengths in order to produce higher resolution than an individual wavelength could provide Polarimeter: measures the polarization of incoming light and can, for example, help in the char- acterization of atmospheric aerosols