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J Environmental Parameters Does EOS collect the erzvironmer'tal parameters that are reflected in the USGCRP research priority framework and related policy issues described in `'Our Changing Planet',? To answer this question, we first considered the overall USGCRP research priority framework, which states three integrating priorities: (1) documentation of Earth system change with observational programs and data management systems; (2) improvement of understanding through focused studies of the controlling physical and biogeochemical processes; and (3) development of integrated conceptual and predictive models. EOS is designed to contribute primarily to items (1) and (2~; EOS data will also be used in the development, validation, and ultimate applications in (3~. The relative emphasis EOS places on process studies and monitoring global change is one that will evolve. At present, EOS is intended to contribute to both, with a stronger focus on process studies. In the long run, it will become a major system for monitoring global change. The changing nature of these roles must be recognized and flexibility must be built into the system so that EOS can adapt. In summary, we find that EOS is being designed to measure environ- mental parameters from space that reflect the USGCRP framework and that will allow researchers to make major contributions to global change research. However, there are general strategy issues that need further development, and we have also identified some specific issues involving instruments. 34

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35 THE MEASUREMENT SYSTEM FOR GLOBAL CHANGE It is generally agreed throughout the international scientific commu- nity associated with global change that adequate documentation of envi- ronmental change on Earth requires a combination of space-based and in situ measurements. "In situ" in this sense means in the atmosphere, on the surface of the Earth, and on and in the oceans. The need for this combination of space- and Earth-based measure- ments is well-documented in reports from the NRC and from NASA The most recent NRC reports come from the Committee on Science, Engi- neering, and Public Policy (Report of the Research Beefing Panel on Remote Sensing of the Earth, 1985~; from the Committee on Earth Sciences and the Ask Group on Earth Sciences of the Space Studies Board (A Strategy for Earth Science from Space in the 1980s and 1990s, Parts I and II, 1982, 1985; Mission to Planet Earth, 1988~. The most recent NASA report addressing the full set of science issues, with recommendations for both NASA and NOAA, comes from the Earth System Science Committee Earth System Science: A Closer Mew, 1988~. The NRC and NASA reports are the work of a representative and broad segment of the U.S. scientific community, and we believe that those reports accurately reflect broadly held views. The two types of measurements complement each other. Space-based measurements can provide a global and synoptic view of Earth's envi- ronmental parameters and processes no. available any other way. In situ measurements document those processes not accessible from space, such as deep ocean currents. Cloud cover prevents many important measurements from being made from space; for a number of process studies, observations are needed within and under clouds. Moreover, the vertical and horizontal resolution and accuracy of certain variables that can be obtained from space are inadequate for certain process studies of importance to global change. Thus there will always be a need for in situ measurements as part of a global change observing system. The combination of space- and Earth- based measurements is essential; neither can provide a complete picture on its own. There are important variables, such as chemical constituents and other internal variables of the ocean, that cannot be measured at all from space; other variables, such as cloud droplet distribution and turbulence, cannot currently be measured well from space. The requirement for complementary measurements has been met for several near-term satellite systems by the development of large coordinated in situ programs. For example, the World Ocean Circulation Experiment (WOCE) was designed to carry out global in situ measurements of ocean circulation at the same time that altimeters and scatterometers will be flown in space on the European Space Agency's (ESA) ERS-1, the U.S./French

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36 TOPEX/Poseidon spacecraft, and the Japanese ADEOS satellite. The first pilot studies of the hydrological cycle under the Global Energy and Water Cycle Experiment (GEWEX) are planned to be carried out at the same time as the flight of the proposed Topical Rainfall Measurement Mission (TRMM). The major studies of GEWEX are proposed to be carried out at the same time as the EOS program. However, an overall strategy for in situ measurements in the time frame of EOS has not been developed. Because of the long lead time necessary for such planning, we conclude that the agencies involved in the USGCRP should begin to develop the plan soon. Without a carefully planned in situ program, including international participation, much of the USGCRP will not be able to take full benefit of EOS and other space-based measurements. EOS IN THE CONTEXT OF OTHER SPACE MISSIONS While EOS will provide an essential part of the total set of observa- tions required for the U.S. Global Change Research Program, not all the environmental parameters required for understanding global change that can be measured from space can be measured by the EOS spacecraft. Therefore, EOS must be viewed in the context of other space-based measurement systems of both the U.S. and other nations participating in global change research that will fly either before or concurrently with EOS. Some parameters must be measured by space-borne instruments on other satellites and in other orbits. The full set of space-based observations that will contribute to improved understanding of global change are expected lo be made by EOS together with numerous other spacecraft. These include NASA research programs such as UARS and TOPEX/Poseidon, the Earth Probes series, and instruments on Shuttle flights, as well as NOAA and DOD operational satellites, and operational and research satellites launched by other nations. An overall international observational strategy that includes all these research and operational satellites and instruments has been discussed, but not yet developed. (See, for example, IGBP Needs for Remote Sensing u: the 1990s and Beyond, a forthcoming report from the Special Committee for the IGBP.) There is a sense of the missions that the respective na- tions or agencies would like to fly, but there are also uncertainties. An international strategy would be useful for ensuring the continuity of ob- se~vations (see Chapter 7 on Continuity and Reliability) and the efficient use of resources. Because NASA has taken the lead in developing the remote-sensing technology for global change research, the agency, working within the CEES, should also take the lead in developing an international strategy for space-borne measurements of global change.

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37 EOS AND THE USGCRP In order to assess the contributions of EOS to the measurements of environmental parameters necessary for documenting global change, it must be recognized that EOS is only part of the space-based system required and that the space-based observations are only part of the total space-based and in situ measurements required. EOS is currently designed to provide a 15-year series of measurements from a sun-synchronous polar orbit with a set of highly developed instru- ments. Such instruments will have higher spectral resolution by orders of magnitude than any available today or likely to be available in the near future. In addition, EOS instrumentation will include advanced versions of existing operational instruments for continuity of measurements. By flying several of these instruments simultaneously, NASA plans to achieve . . a major Improvement in the description of global physical and biogeochem- ical phenomena. The global change research community looks to EOS to provide new technology for measuring parameters not adequately studied today, as well as to continue the measurements of parameters that are reasonably well understood. The objective is for EOS to provide the user community (science, industry, policy) with the first comprehensive long- term measurement and data system specifically aimed at global change issues. The proposal for a 15-year series of satellites focused on study of the Earth raises issues of programmatic strategy. EOS has a dual character, combining typical research missions with others that have more of the characteristics of operational monitoring missions, such as those flown by NOAA and DOD. Research missions are typically strongly dependent on a few individuals who devote portions of their careers to them, whereas operational missions are designed to deliver data to other users on a reliable and routine basis. Because all EOS data are intended to be widely shared, a more operational strategy is required-even for the pure research objectives. Furthermore, the general strategy and the specific instrument details and algorithms should be fully documented. During the development of the EOS concept, NASA formed a Science Steering Committee that produced the volume entitled From Pattern tO Process: The Strategy of the Earth Observing System. That report proposed the Implementation, individual measurements, and synergistic measurement strategies for EOS. In the interim, however, much has changed. New instrument concepts have been developed; others have been discarded. A competitive selection process has been conducted naming instrument investigators and teams to perform interdisciplinary studies. A budget profile now defines a funding envelope for investigators, instruments, and spacecraft.

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38 It is now vital to begin the process of updating the earlier work of the Science Steering Committee to develop the successor to From Pattern to Process. As indicated earlier, the successor should detail the observational strategy for space-based observations and the ancillary in situ and ground- based measurements that accompany them. The required strategy would go beyond From Pattern to Process, however, in that it should include in situ measurements. Consequently, while NASA should participate in its preparation, responsibility for its development should fall to the CEES. The GEWEX program provides an example of a coordinated inter- national observational strategy to support research of the type envisioned. GEWEX relies first on limited in situ and satellite (TRMM) observations for a pilot study to be followed by an extensive ground-based measurement program complemented by EOS data. The observational strategy should indicate how each observing system and measurement contributes to the overall scientific objectives of the USGCRP. In particular, it should show how each measurement, with its associated accuracy and resolution in space and time, will contribute the desired end product of global or regional data sets that will advance our understanding and predictive capability of the Earth system. Perhaps most important, it should allow for the evolution of observational goals and technology and should be updated from time to time. We can refer to this documentation as providing "traceability". The new study must scrupulously state the objectives and rationale for the deployment of the series of instrument suites, and provide with refer- eed journal care the traceability to the detailed assumptions and analyses upon which the objectives and rationale are based. As the study evolves and changes, it is important that the strategy be comprehensive and clear. Changes stemming from either scientific, technological, or financial recon- sideration of the mission must be understood and thoroughly documented. The simplest statement of the objective of the EOS program is that it will advance mankind's understanding of the continuing evolution of the planet. Unlike most scientific investigations, the value of EOS will lie in itS aggregate accomplishment, rather than in the important but individual achievements of the respective investigator teams. Thus documentation that aids and guides the aggregate accomplishment, to which newcomers can also refer, is vital. Therefore, we recommend that NASA initiate immediately the development of a documentation plan, and quickly thereafter the documentation itself that will be required in this multidecadal program. Summary Recommendations In view of the fact that EOS is a 15-year program, a fully- documented strategy and specification of instruments must be developed and updated

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39 as required. This is the only way that EOS can serve as an intermediate step between the research missions of the past and the operational systems of the future. As indicated earlier, the set of instruments under consideration for flight appears to be capable of providing a comprehensive set of mea- surements of high priority environmental parameters. The complete set of measurements eventually to be made from EOS spacecraft will depend on the successful development of the respective instruments, as well as on other factors. In the sections below, we briefly summarize the contribution of EOS measurements to the objectives of the USGCRP. It should be noted at the outset that specific agency planning will not necessarily have the same framework as that developed by the USGCRP, but the specific elements of agency programs should be relevant to the overall framework. Each of the specific elements of the EOS scientific plan contributes to one or more of the elements of the USGCRP. Because EOS has been proposed as a major contribution to the US- GCRP, the overall strategy for the program and the selection of instruments and orbit should be optimized on the basis of USGCRP priorities. Review processes should be set up to ensure that this close connection is made and maintained. A clear strategy and process should be established by which instruments are selected. This strategy would determine the measurements to be made and, therefore, the individual and aggregate research to be done. The specific research objectives, and possibly even the general goals, of the USGCRP will change as more is learned about the subject. The technology of remote sensing is also likely to change over the life of the program. Although continuity of specific data sets will be an important consideration, it may be desirable to alter the instruments or the platforms, or both, at some time in the future. Currently, the program contains no process that would enable it to evolve in response to new scientific understanding or technological developments. CONTRIBUTIONS TO SPECIFIC USGCRP SCIENCE PRIORITIES Because we have been asked to consider the contribution of EOS to the USGCRP, we use the set of priorities listed in the FY 1991 version of Our Changing Planet. The USCGRP framework provides for specific science priorities in seven interdisciplinary areas: (1) climate and hydrologic systems; (2) biogeochemical dynamics; (3) ecological systems and dynamics; (4) Earth system history; (5) human interactions with the Earth system; (6) solid Earth processes; and (7) solar influences. NASA has described ills program in slightly different terms. As currently planned, EOS data are expected to contribute in a major

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40 way to areas (1), (2), (3), and (6); less extensive contributions are expected to be made to areas (4), (5), and (7). The specific contributions are discussed in the sections below. In each section we quote the policy- relevant questions as noted in the FY 1991 version of Our Changing Planet, and then summarize current plans and proposals for space missions to address them, including the proposed EOS contributions. In the discussion of particular instruments, it should be noted that in some cases the process of selecting between competing instruments is still under way. In every case, we emphasize that we refer to the generic class of instrument represented by the particular example cited; naming a specific instrument is not to be taken as an endorsement of that instrument over competing instruments for flight on EOS. Climate and Hydrologic Systems 1. What is the role of clouds in the Earth's radiation and heat budgets? Near-term Plans The ongoing programs for monitoring the Earth's radiation budget, the Earth Radiation Budget Experiment (ERBE) and the International Satellite Cloud Climatology Program (ISCCP), if continued until the launch of EOS, will provide continuity for this important parameter, which is one of the principal diagnostics of the "greenhouse" effect. ~ monitor the Earth's radiation budget properly, daily global data from two polar orbits (a.m. and p.m.) and a mid-latitude inclined orbit (50 to 60 degrees) are required. It should be noted that a joint French/Soviet radiation experiment, the Scanner for Radiative Budget (SCARAB), is scheduled to be flown in 1991. This experiment will help to provide a follow-on to ERBE in the early 1990s. Unless another Earth radiation budget measurement mission is flown, however, there will be a several year gap in such data between the end of the SCARAB mission and the beginning of EOS. EOS Plans The EOS instrumentation makes a major contribution to answering the question about the role of clouds in climate. The high degree of temporal and spatial variability of cloud-atmosphere radiation interactions and fluxes of heat and energy at the surface must be measured accurately. The EOS instruments promise to provide accurate atmospheric temperature profiles with the Atmospheric Infrared Sounder (AIRS) and the Advanced Microwave Sounding Unit (AMSU). The current atmospheric temperature and water vapor profiles provided by the operational HIRS/AMSU system

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41 constitute valuable data where other measurements are sparse, as in the southern hemisphere. To date, however,- they have proved to be of less utility where dense networks of in situ observations exist. The instruments proposed for EOS promise higher spatial and spectral resolution as well as improved accuracy. The Clouds and Earth's Radiant Energy Systems (CERES) radiome- ter is designed to determine broadband shortwave and longwave top- of-atmosphere radiances. The High-Resolution Microwave Spectrometer Sounder (HIMSS) would establish water content of clouds over the ocean. The Moderate Resolution Imaging Spectrometer (MODIS) in its nadir looking mode is intended to provide spectral information needed for de- termining physical cloud properties and cloud height. The Earth Observ- ing Scanning Polarimeter (EOSP) would determine aerosol composition. The Multiangle Imaging Spectro-Radiometer (MISR) promises, through its multi-angle viewing capability, to provide the bulk radiative properties of aerosols in the shortwave spectral region. The current plan for EOS has adequate instrumentation for monitoring the Earth's radiation budget from a p.m. polar orbit. Data from an -a.m. polar orbit could be provided by the European Polar Orbiting Platform (EPOP) or the NOAA polar orbiting satellite series. An inclined-orbit instrument is planned for the Space Station, in a tropical orbit. At 28 degrees, the inclination of the Space Station's orbit is too low to complement coverage in the high latitude regions. Moreover, uncertainties in the time of the Space Station launch may reduce coverage unacceptably. EOS includes plans to monitor solar output with the Solar Stellar Irradiance Comparison Experiment (SOLSTICE) and the Active Cavity Radiometer Irradiance Monitor (ACRIM). SOLSTICE would provide pre- cise daily measurements of the full disk solar ultraviolet irradiance; ACRIM would monitor the variability of total solar irradiance with state-of-the-art . . accuracy ant precision. Finding A gap in measurements of the Earth's radiation budget will occur in the mid-199Qs if no additional mission is proposed. A follow-on to the SCARAB experiment at an adequately inclined orbit will be needed. Such a mission would be suitable for the Earth Probes series. 2. How do the oceans interact with the atmosphere in the storage, transport, and uptake of heat? Near-term Plans Before EOS is available, a number of remote sensing missions are

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42 expected to study ocean circulation and air-sea fluxes of energy and mo- mentum. They include the precision altimetry mission, TOPEX/Poseidon; the sea-surface temperature measurements, altimetry, and a surface wind measuring scatterometer on the European Space Agency's ERS-1; the NASA scatterometer on the Japanese ADEOS; and an altimeter to be flown by the U.S. Navy on a Special Purpose Inexpensive Satellite (SPIN- SAT). These are to be complemented by ongoing operational measurements of sea surface temperature and humidity from the NOAA and Defense Me- teorological Satellite Program (DMSP) programs. The various missions are intended to provide data for existing and planned field programs such as the World Ocean Circulation Experiment. EOS Plans The primary EOS measurements are intended to provide a variety of data on ocean currents, surface winds, ocean and atmospheric tempera- tures, and near-surface humidity for air-sea flux studies. They include sea- surface temperature from the Moderate Imaging Spectrometer in its nadir mode, and from the High Resolution Microwave Spectrometer Sounder. Both the classical fan-beam (STIKSCAT) and advanced dual pencil-beam (SCANSCAT) scatterometer designs are being considered for EOS. Surface topography would be measured from an altimeter. Air temperature and humidity near the sea surface would be measured with the Atmospheric Infrared Sounder and the Advanced Microwave Sounding Unit. 3. How will changes in climate affect temperature, precipitation, and sod mozsmre patterns, and the general distribution of water and ice on the land surface? Near-term Plans Specific missions proposed in this general area are the joint U.S./ Japanese Topical Rainfall Measuring Mission (TRMM) and a planned French mission, Bilan Energetique de 1a Systeme Tropical (BEST). Each mission proposes to carry a major radar sensor for measuring rainfall directly, and together they would form the space-based portion of the Global Energy and Water Cycle Experiment, which is scheduled to begin in the mid-1990s. Of the two satellite projects, TRMM is more fully developed in its technical planning. EOS Plans The primary EOS measurements in this area are for temperature and water vapor sounding from AIRS and AMSU. Precipitation, sea ice, and

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43 Spectrometer Sounder (HIMSS). Glacier profiles would be measured by the Geosciences Laser Ranging System (GERS). Water vapor fluxes would be monitored by the scatterometer and HIMSS over the oceans. Over land, tropospheric winds, aerosols, and cirrus clouds would be monitored by the Laser Atmospheric Wind Sounder (LAWS). Vegetation characteristics would be measured by the Moderate Resolution Imaging Spectrometer (MODIS), the High Resolution Imaging Spectrometer (HIRIS), and the Intermediate Thermal Infrared Radiometer (ITIR). Recent aircraft nights demonstrate that soil moisture can be mea- sured from space with a Synthetic Aperture Radar (SAR). Monitoring soil moisture is important for study of the hydrologic budget, but is not in- cluded in current EOS plans because of budget considerations. Although soil moisture can- and should be measured on the ground, only satellite measurements can provide global coverage continuously. The LAWS in- strument will also require extensive development of technology to achieve the highest level of proposed precision. Engineering considerations presented by NASA suggest that the SAR instrument contemplated for EOS would not be compatible with a multi- instrumented satellite. Therefore, the potential contributions of a free- flying SAR mission should be carefully considered in the context of global change research. 4. How can the reliability of global- and regional-scale climate predictions be improved? The EOS and other space-based observing missions are expected to make major contributions toward answering this question in a number of ways. First, improved understanding of processes obtained from the respective missions would be incorporated into better process descriptions in models. Second, data from the missions-either archived directly or assimilated into the data streams of current global weather prediction systems- would provide climate data sets invaluable for validating models to be used for projecting climate change. Third, many of the boundary conditions for models used for climate projections must be derived and improved from satellite observations. Finally, predictions for the satellite data can provide initial conditions needed for the shorter seasonal to interannual time scales. Biogeochemical Dynamics 1. What is the relative importance of the oceans and terrestrial

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44 biosphere as sinks for fossil fuel carbon disciple, and how do they change with time? Near-term Plans Monitoring the distribution of oceanic chlorophyll and the properties of terrestrial vegetation provides information on gas and nutrient exchange between the atmosphere and ocean, freshwater and terrestrial biosphere, and on oceanic and terrestrial carbon storage. The role of biological systems in global change is one of the least understood. The precursor missions and the EOS planning in this area are key parts of the global change research program and should have high priority. The international Joint Global Ocean Flux Study (JGOFS) has been developed and has a field program now beginning. Currently, the Sea- viewing Wide Field Sensor (SeaWiFs) ocean color mission is planned to support JGOFS. Flight of the Shuttle Imaging Radar (SIR-C) is important for studies of land vegetation, and will be complemented by field studies of the World Climate Research Program (e.g., the International Satellite Land Surface Climatology Program and the Global Energy and Water Cycle Experiment) and the International Geosphere-Biosphere Program (e.g., the Joint Global Ocean Flux Study). EOS Plans The Moderate Resolution Imaging Spectrometer (MODIS) in both its nadir-viewing (MODIS-N) and side or tilt-viewing (MODIS-T) implemen- tations is the essential next step for measuring ocean and land chlorophyll concentration. The high spectral resolution of the MODIS is intended to provide measurements not possible before. The MODIS, the high,spectral resolution HIRIS, the Intermediate Thermal Infrared Radiometer (ITIR), and the Multi-Angle Imaging Spectro-Radiometer (MISR) are expected to collect land vegetation measurements. Biogenic gas emissions could be measured by the Tropospheric Emission Spectrometer (TES), and vegeta- tion structure could be monitored with the NASA SAR. Findings Current plans omit important space-based measurements that would be valuable for understanding the relative importance of ocean and terrestrial ecosystems as sinks for carbon dioxide. First, in the near term, the JGOFS program would benefit from the flight of the next generation of ocean color instrument, the proposed SeaWiFS. Second, the SAR has potentially important roles to play in making measurements of biological processes on land.

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45 2. What are the major sources responsible for the current increases in atmospheric nitrous oxide and methane? 3. What are the implications for stratospheric ozone global) and in polar regions increased concentrations of chlorine and bromine? Near-term Plans In the near term, the Upper Atmosphere Research Satellite (WARS) and the continuing in situ Global Tropospheric Experiment (GTE) with its Pacific Exploratory Mission in 1991 and an Atlantic program in 1992-will address these two questions in the interval before the first EOS satellite is launched. EOS Plans For these studies, it is important to monitor solar radiation to the earth. It is proposed that solar output be monitored by the Solar Stellar Irradiance Comparison Expenment (SOLSTICE) and the Active Cavity Ra- diometer Irradiance Monitor (ACRIM). SOLSTICE should provide precise daily measurements of the full disk solar ultraviolet irradiance; ACRIM is designed to monitor the variability of total solar irradiance with state-of- the-art accuracy and precision. The Tropospheric Emission Spectrometer is proposed to measure tro- pospheric trace gas species. This high-resolution infrared imaging spec- trometer would generate three-dimensional profiles on a global scale of virtually all infrared-active species from the surface to the lower strato- sphere. The Measurement of Pollution in the Troposphere (MOPING) and lloposphenc Radiometer for Atmospheric ChemistIy and Environ- mental Research (TRACER) instruments are intended to monitor carbon monoxide in the troposphere. The High-Resolution Dynamics Limb Sounder (HIRDLS) is expected to observe the global distribution of temperature and concentrations of ozone, water vapor, methane, various oxides of nitrogen, CFCs, and aerosols in the upper troposphere, stratosphere, and mesosphere. The Spectroscopy of the Atmosphere Using Far Infrared Emission (SAFIRE) instrument is inended to provide simultaneous measurements of HO, NO=, ClO=, and Brow species. The Microwave Limb Sounder (MLS), an enhanced version of an instrument on WARS, would provide vertical profiles of all molecules and radicals believed to be important in the ozone destruction circle in the stratosphere and mesosphere. The Stratospheric Wind Infrared Limb Sounder (SWIRLS) is expected to provide direct measurements of stratospheric winds by measurements of Doppler shift. This would allow correlation of atmospheric dynamics and chemistry in the stratosphere. Together with the Stratospheric Aerosol and Gas Experiment

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46 (SAGE III) instrument, a full set of data should be provided to help answer questions about these phenomena. Ecological Systems and Dynamics 1. What ecological systems are most sensitive to global change, and how can natural change in ecological systems be distinguished from change caused by other factors? 2. What are the likely rates of change in ecological systems because of global change, and will natural and managed systems be able to adapt? ~, 3. How do ecological systems themselves contribute to processes of global change? Near-term Plans The satellite data required to address the above questions comes in the near term from research and operational missions. The ongoing NOAAlAVHRR, Landsat, and SPOT programs provide detailed informa- tion on ecological systems primarily on land. Data from these programs can be used to monitor changes in land use patterns and the areal extent of vegetation representative of ecosystem types. As described earlier, current proposals include the flight of an ocean color instrument. EOS Plans The EOS contribution to these research objectives should be made by the same instruments that are intended to contribute to research on biogeochemical dynamics: MODIS-N and -T. HIRIS, MISR, and ITIR. The SAR instrument, which could make additional contributions in this area, is not included in current plans for EOS. The EOS instruments would provide data similar to those of the NOAAlAVHRR, Landsat, and SPOT programs but with higher spectral resolution and accuracy for studying ecological processes in detail. Earth System History 1. What are the natural ranges and rates of change in the climate and environmental systems? 2. How rapidAy have ecosystems adapted to past abrupt transitions in climate?

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47 3. Do past warm intervals in Earth history provide appropriate scenarios to test model predictions of future global warming? The answers to these questions are expected to come primarily from in situ studies of cores from continental, ice, and ocean drilling. Current space- based observations cannot directly reveal global changes in the Earth's history, but they can provide data useful for improving understanding of solid Earth processes, which would help to illuminate that history. (See the section on Solid Earth Processes below.) lIuman Interactions 1. What kinds of empirical data are needed to measure and under- stand human interactions in global change? The EOS program should provide data that will be potentially useful for the human interactions aspect of the USGCRP. For example, the very high resolution instruments such as HIRIS could provide information on direct human interactions with the environment (e.g., deforestation, coastal and estuarine pollution, agricultural practices). EOSDIS is expected to be an important source of such data for the study of the effects of human activities on the environment. In order that the use of these data be effective, there will be a need for close interaction between researchers who will use these data for this purpose and the EOSDIS designers to ensure that the system provides the required information. 2e How and why do human beings and human systems influence physical and biological systems? The answer to this question drill depend partly on the use of satellite data, which can provide an important means of studying and monitoring the effects of some human activities on the environment. Solid Earth Processes 1. How do different coastal regions respond geologically and ecolog- ica11y to higher sea level, and how can the contributions from changes in climate (e g., glacier melting and ocean warming be differentiated from those due to tectonic processes? 2. What are the magnitude, geographic location, and frequency of volcanic eruptions and their effect on climate?

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48 3. How do permapost regions of the Northern Hemisphere respond to climate warming? Near-term Plans The near-term activities in this area include the precise positioning provided by the Global Positioning System, the Very Long Baseline Inter- ferometry, and Laser [lacking of the LAGEOS I and II satellites. These missions support the use of global tide gages and satellite altimeter mea- surements of sea level change, as well as altimeter measurements of changes in global ice mass. Imaging of volcanoes and other regions will be pro- vided by various operational satellites (AVHRR on the NOAA satellites and imagers on Landsat and SPOT). Emissions from volcanic eruptions will be monitored by the operational meteorological satellites and the SAGE instruments. Beginning in 1991, UARS will provide useful data on the stratosphere. EOS Plans Crustal movement and tectonic plate deformation are proposed to be monitored by the Geoscience Laser Ranging System (GLRS), which will early a laser system, an optical tracking system, and a precise navigation system for use with arrays of reflectors on the ground. The Altimeter and Global Positioning System Geoscience Instrument (GGI) should be a source of accurate ice and ocean topography. The SAR, which is currently not budgeted, could provide all-weather studies of surface processes. Surface mineral identification, soil characteristics, and geothermal monitoring would be carried out with the ITIR and HIRIS. Monitoring of trace gases and aerosols is intended to be done with SAGE, TES, and HIRIS. EOS data should be useful in characterizing the nature of volcanic emissions, for monitoring the mechanisms of plate motion over long periods, and for understanding regional uplift, subsidence, and associated coastal processes. Changes in the Earth's rotation and length-of~ay could be monitored by EOS with high resolution geodetic techniques, while the deep- seated processes in the Earth that cause these changes may be inferred from studies of the Earth's magnetic field. EOS sensors are expected to monitor surface processes and detect areas of current or potential desertification and erosion. Solar Influences 1. What aspects of solar variability are influencing the stratospheric ozone layer?

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49 2. What impact do other inputs, fig, panicles, have on the upper atmosphere and how are they coupled to other a~nosphenc regions? 3. How does the sun's output vary and what is its impact on terrestrial climate? Near-term Plans Providing answers to these questions will require accurate measure- ments of solar variability at all wavelengths and continuing monitoring of appropriate chemical species in the upper atmosphere. These measure- ments are being made by NOAA operational satellites. Near-term plans include instruments on WARS, as described earlier in connection with the discussion of biochemical dynamics. The data are needed for further de- velopment of theoretical models of solar-terrestrial interactions that affect global change. EOS Plans Of particular importance here is ultraviolet radiation from the sun. The EOS Solar Stellar Irradiance Comparison Experiment (SOLSTICE) is intended to monitor the full disk solar ultraviolet irradiance as a follow-on to a similar instrument carried by WARS. The EOS Stratosphere Aerosol and Gas Experiment III (SAGE III) is proposed to measure profiles of aerosols, air density, and a number of constituents. It is an extension of the successful SAGE experiments flown earlier and planned for WARS. SAGE III is also planned for flight on the Space Station to provide full coverage and back-up measurements. EOS proposes to measure solar irradiance with a radiometer (the Active Cavity Radiometer Irradiance Monitor) and with an ultraviolet irradiance measurement. Each of these is a source of continuity with UARS measurements.