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EARTH'S ENVIRONMENT* INTRODUCTION The use of space vehicles as platforms from which to observe the earth's environment has led to a new perspective of our atmosphere. As a result of observations from space and other advances, significant progress has been made in our ability to observe and forecast changes in the earth's environment. In preparing this report, the Panel examined the present state of scientific understanding in four major areas of interestâupper-atmospheric research, global chemical cycles, weather, and climateâfor the purpose of defining requirements for future observational data. In each of these four areas, the Panel indicates the characteristics that would be needed in a space station or space platform to meet future data requirements. Advances in technology that should be explored are identified at the end of each section. Orbit considerations and the role of man in space are discussed where appropriate. *The Panel acknowledges the assistance of many persons, especially Dixon Butler and Dudley McConnell of the National Aeronautics and Space Administration, James Purdotn and Harold Yates of the National Oceanic and Atmospheric Administration, and Norman Phillips of the National Weather Service. l9
20 UPPER ATMOSPHERIC RESEARCH Introduction A major use of space systems now and for the foreseeable future is to observe and measure the characteristics of the upper atmosphere (principally the stratosphere). The general state of understanding of this area has been recently reviewed in The Stratosphere l98l: Theory and Measurements (World Meteorological Organization,l98l). During the past decade, the stratospheric ozone layer has become a focus of concern and a matter of regulatory activity. One concern is that humanly caused pollutants in the stratosphere could decrease the average amount of ozone, thereby admitting increased amounts of biologically harmful ultraviolet light to the surface of the earth. After atmospheric scientists predicted that chlorofluorocarbons diffuse to the stratosphere and contribute to ozone depletion, the Environmental Protection Agency (EPA) regulated some uses of these substances. A second area of concern arises from the fact that, in addition to screening out harmful radiation, the ozone layer plays a part in controlling the thermal structure of the stratosphere and mesosphere. Both dynamic and radiative mechanisms have been identified through which long-term changes in ozone could possibly affect weather patterns of the lower atmosphereâand hence climate. Thus the study of the stratosphere has taken on a sense of urgency. There is need to predict reliably the impact of various substances generated by an industrial society on stratospheric chemistry. What Is Required for Advancement? Theory Needed There is need for continued effort in atmospheric modeling. During recent years, one- and two-dimensional modelsâphotochemical models with a highly parametric treatment of dynamicsâhave been developed and used to describe and forecast the state of the upper atmosphere. The chemical mechanisms incorporated in these models are reasonably realistic, although in many cases-they have not been validated by comparisons with in-situ stratospheric
2l measurements. Although these models may prove to be correct in certain types of calculations, their reliability in such applications may be demonstrated only after significant stratospheric changes have taken place. Therefore, an alternative approach is being used in which the simplified parameters used in the earlier models are replaced with explicit physical or chemical calculations. These new models operate in three dimensions, but still use primitive equations of dynamics, and have chemistry coupled to the dynamics as well. Developing such a model is a difficult task. However, in a model with consistent calculations of the important processes, the validation of each process results in considerable confidence in the total model output; thus, these new models may achieve a level of credibility that will make them more useful than the older, simpler models. Hence arise the need for continuing vigorous effort on three-dimensional models and the challenging requirement to accumulate extensive global data sets, including simultaneous observations of stratospheric structure, motions, and composition. Laboratory Work Required The measurement of key chemical reaction rates and spectroscopic parameters in upper-atmospheric research has progressed well. In the future, measurement of the variability of all relevant rate constants with temperature and pressure will be essential. Further, development and utilization of remote techniques for globally observing the upper atmosphere depend on measuring radiation or absorption by trace molecules (e.g., H202, CIO and N02); the determination of the spectroscopic parameters of such molecules represents another important area of laboratory research. Finally, there is a need for measurements of the kinetics of gas-to-particle conversion for several important gases found in the upper atmosphere. Needed Field Measurements There is need for simultaneous upper-atmospheric observations on a global scale. Important information on the presence and distribution of many substances in the
22 upper atmosphere has been provided by measurements in addition to those from satellites. For example, balloon-borne sensors have confirmed the presence and measured the relative abundances of chemical species that interact with one another in the catalytic cycles governing ozone destruction (e.g., NO, N02, OH, Cl, CIO, HCl). In addition, balloon flights have served as the principal means for developmental testing of upper-atmospheric remote sensors. Aircraft have provided valuable data on atmospheric dynamics, and in particular on exchange between the stratosphere and the troposphere. Balloon flights and aircraft will continue to be needed as important sources of data for calibrating remote observations and for making detailed measurements that are beyond the present abilities of satellite remote sensors. However, it is only with simultaneous observations on a global scale that the complex interplay of chemistry and dynamics of the upper atmosphere can be truly studied. The only practical means of collecting this data set is by remote detection from space. Research satellites have demonstrated that remote techniques can be used to observe some of the important species, such as 03, NO, N02, and H20, as well as aerosols. The next step in understanding the stratospheric ozone question requires simultaneous observations to check the completeness of the three-dimensional model and to validate the treatment of the interactions. The required data set must include measurements of a larger list of key species (HN03, N20, F-ll, F-l2, HCl, CIO, H202, CH4, in addition to 0-j, N2, N02, and H20), together with measurements of upper-atmospheric winds, stratospheric thermal structure, and solar output. NASA's planned Upper Atmosphere Research Satellite (UARS) is designed to make the needed atmospheric measurements. After UARS, the next major step needed is development of a system that will permit continuous data sets to be accumulated over a decade or more. Characteristics Required of a Space Station or a Space Platform There are several ways in which a space station or space platform could prove useful in achieving long-term upper-atmospheric measurements. One involves cooling
23 systems. Should cooled sensors prove essential for long-term observations, on-orbit replenishment of cryogens may be imperative. On the other hand, active cooling systems may be more effective, even though they are heavy and high in energy consumption. Another problem of long-term observations with any quantitative system would be the need to validate instrument calibration periodically. Direct access to the instruments would greatly improve the reliability and credibility of long-term observations. Repairing failed instruments on orbit would perhaps prove to be cost-effective, but further study would be required to establish this. All of these activities would require novel features in instrument design and an on-orbit infrastructure that would make them both possible and affordable. Human presence on-orbit might prove cost-effective for servicing, replenishing, and calibrating. However, caution would be required in designing the human interface, since observations of the type described in this section would be quite sensitive to the chemical or particulate contamination and the vibration that would be associated with human presence. Acquisition of the needed long-term global observations of the upper atmosphere may require a low earth orbit that provides limb-scanning coverage at various local times. There is also the possibility that the needed measurements would require a number of special-purpose remote sensors making simultaneous, collocated observations. Requirements of some or all sensors for a clear field of view could affect the size or configuration of a platform or a station used for upper-atmospheric observations. Technologies Needed Beyond those to be used on UARS, technologies needed in upper-atmospheric observations can be divided into three categories: remote sensing, data systems, and operational support. Examples of remote sensing technology include the development of remote-measurement techniques for OH and N02 and the measurement of HCl with better coverage (not using occultation). Various techniques, including lidar, need to be considered to make possible higher precision or higher resolution or new kinds of observations. The capacity of data systems must be increased to handle the multiple-data-stream mode of operation that
24 will be increasingly required if simultaneous measurements of a large number of species and parameters are to be made. The need for high-spectral-resolution measurements and the need to survey broad spectral regions to determine upper-atmospheric composition have the potential for creating large data streams consisting of new kinds of data (for example, complete interferograms). Data systems that included onboard processing might be essential in order for such devices to be used with maximum effectiveness. Operational support technologies would be needed for the new generation of observations discussed here to become a reality. Larger space-borne power systems may be required by lidar instruments and stable, large structures would have to be developed to permit flying a large collection of sensors on one spacecraft. GLOBAL CHEMICAL CYCLES Introduction This section focuses on the application of space systems to the study of the lower-atmospheric (i.e., tropospheric) portion of global chemical cycles. The preceding discussion of upper-atmospheric chemistry is separate from this section on the troposphere only for convenienceâthese systems are in fact coupled, and research in the two areas needs to proceed in parallel. Cycling of chemical species in the troposphere is frequently characterized by emission from the earth's surface of chemicals in partly oxidized states (e.g., CH4, NHj, H2S), transformation of these compounds by the atmospheric free radical OH to highly oxidized states (e.g., COo, UNO-}, I^S04), and subsequent removal of the oxidized compounds from the atmosphere by rainout and washout. Global chemical cycles are closely coupled with the global hydrological cycle. Thus, complete understanding of global chemical cycles requires a corresponding understanding of hydrology as well as of the chemistry of the air and the oceans. Global chemical cycles affect many areas of human and environmental concern, including human health, agriculture, weather, and climate. Concerns range from global questions (e.g., Will increases in carbon dioxide
25 in the upper atmosphere cause climate change?) to more localized problems (e.g., How does acid rain occur, and what are the most effective steps to reduce its occurrence and resulting damage?). A quantitative understanding of biogeochemical cycles and their time change will help to determine the impact of human activities on the biosphere and to prevent or ameliorate the unintended consequences of human activity. What Is Required for Advancement? Theoretical Studies* Theoretical studies of global chemical cycles are an essential element of an effective research strategy. Tropospheric photochemical models for instance, have largely been responsible for delineating the central role of free radicals such as OH in the atmospheric chemical systems. A major goal for the future is to make these models chemically more sophisticated and dynamically more realistic. Studies are needed of the coupling of gas-phase atmospheric chemistry with cloud processes, including cloud microphysics, liquid-phase cloud chemistry, and cloud dynamics. The mechanisms that couple atmospheric chemistry with ocean and soil chemistry as well as with biospheric processes also need to be addressed. More sophisticated two- and three-dimensional models that simultaneously treat chemistry and atmospheric dynamics are needed. Laboratory Studies Laboratory studies to determine the kinetics of a wide variety of gas-phase, and aqueous-phase, reactions under atmospheric conditions have been and continue to be an important research area. One important example is the need to study the kinetic mechanisms that control the oxidation of gaseous S02 to dissolved SO4 in a cloud. *For a more detailed presentation, see Seinfeld and coauthors, l98l.
26 Field Measurements Field measurements are required to develop a global chemical data base, to quantify the exchange rates of chemicals between the biosphere, atmosphere, lithosphere, and hydrosphere, and to test the accuracy of predictions using atmospheric photochemical modelsâsuch as predictions concerning the free radical OH. Such measurementsâeither ground-based, shipboard, or airborneâhave already helped establish a rough understanding of the latitudinal and longitudinal distribution of many atmospheric species of interest (e.g., 03, CO, CH4, HN03, S02, CH3, CCl3). Unfortunately, our ability to use space technology to study atmospheric chemical composition is at present limited by the state of the art of remote sensing technology. Based upon recent reports (e.g., National Aeronautics and Space Administration, l979; Keafer, l982), it appears likely that by the l990s it will be possible to measure remotely from space only a small subset of the tropospheric species listed above. This subset may include only CO, CH4Oj, HNOg, H20, N02, S02, NH-j, and aerosols. Nevertheless, the ability to measure remotely even this limited set of atmospheric species could significantly enhance our global chemical data base. Thus, the Panel recommends that efforts be continued to develop tropospheric remote sensing technology; these efforts should include the use of the Space Shuttle to test each instrument under flight conditions. To calibrate the remote measurements, as well as to monitor those substances that can only be detected by sample analysis, a field measurement program using aircraft and ground-based observation platforms will be needed in conjunction with the development of the remote sensing technology. Possible Uses of a Space Platform or a Space Station Once a remote sensing technology for tropospheric chemical species has been successfully developed and tested, the instrumentation could be placed very usefully on a space platform. The advantages of a space platform would include: (l) the ability to have a large number of instruments on a single platform so that simultaneous measurements could be made of several atmospheric species and related meteorological parameters such as temperature,
27 winds, cloud cover, and precipitation; (2) the ability to have a crew periodically visit, service, and calibrate the instrumentation, making it possible to obtain continuous data over a long time period and thus to study atmospheric temporal variability; and (3) the ability to use large, powerful, and heavy active sensors (such as lidar) to measure species that cannot be sensed by passive techniques. For remote sensing of the lower atmosphere, a space platform should be placed preferably in a near-polar orbit that would afford complete global coverage. However, a high-inclination orbit (e.g., 57Â°) would probably yield a large body of valuable information. Spacecraft in low-inclination low earth orbits would be useful for tropical measurements; however, the usefulness of a low-inclination orbit (e.g., 28.5Â°) alone would be limited. Beyond the l990s, another very helpful configuration would be a series of platforms in various geosynchronous orbits that would permit study of the effects of episodic events (such as forest fires and rain systems) on chemical composition, and that would also allow for monitoring the dispersion of man-created emissions in the global atmosphere. At this time, the Panel has identified only periodic maintenance and calibration tasks for which human presence in space would be helpful in the operation of remote sensors for environmental observations. Technologies Needed The greatest technological need in the study of tropospheric chemical cycles is the development of remote sensing technology. The current state of the art and likely near-future advances in this technology have been summarized in several recent reports (including Tropospheric Passive Remote Sensing [Keafer, l982]; Shuttle Atmospheric Lidar Research Program [National Aeronautics and Space Administration, l979]; and The Global Troposphere: Biogeochemical Cycles, Chemistry, and Remote Sensing [Levine and Allario, l982]). Based on these reports, the following list indicates the remote sensing techniques that presently look most promising for measuring data on global chemical cycles.
28 Technique To Measure Optical filter radiometer Temperature, H20, 03 aerosols Gas filter radiometer Laser heterodyne Orbiting spectrometer Interferometer Lidar CO, CH4, and possibly HNO-j, NO, H2CO H20, CH4, and possibly 03, HN03 Spectral survey Spectral survey 03, aerosols, temperature, winds, possibly N02 and S02 WEATHER Introduction For more than l00 years, the United States has operated an observing system for weather forecasting. Today this system includes data from passive radiation sensors on geostationary and polar-orbiting satellites. These satellite data include information on clouds (from visual and infrared images), on vertical profiles of temperatures and moisture (infrared supplemented by some microwave on the polar-orbiter spacecraft), and on sea surface temperature (infrared). Half-hourly cloud images from the geostationary satellites enable wind estimates to be made in those parts of the atmosphere where clearly identifiable cloud elements exist and are trackable from one image to the next. Under the auspices of the World Meteorological Organization (WMO) and International Council of Scientific Unions (ICSU), the Global Atmospheric Research Program, culminating in the Global Weather Experiment in l979, provided the framework for development and testing of global remote sensing techniques, for improvement of models, and for acquisition of the most advanced computer systems by meteorological research groups and weather
29 services. The improved understanding and capability that resulted from these activities are increasing the ability to forecast large-scale features of the weather. Forecasting for six to eight days is done routinely. A recent study by Lorenz (l983) concludes that further improvement of initial analyses (i.e., data) could extend this predictability limit to about two weeks. On the nonsynoptic scaleâthe mesoscale and storm scaleâthere is neither the long history of continuous observations that exists on the synoptic scale, nor the ability to model realistically the complex and nonlinear processes that become more and more important as one moves to progressively smaller scales in the atmosphere. This section discusses the possible roles for space stations or space platforms in producing further improvements in synoptic-scale forecasting and in undertaking the range of activities required to develop a national capability in mesoscale observing and forecasting. What Is Required to Advance the Nation's Weather Services? In the United States, there are needs for weather forecasts over a wide range of time and spaceâi.e., from minutes to weeks to climatic time scales, and from tornadic and airport-size to global scales. The needs include those of public safety (warnings of hazardous weather such as hurricanes, tornadoes, flash floods, and severe thunderstorms); those of various industries for weather information to aid the efficiency of their operations (e.g., air, land, and sea transportation; agriculture; construction; energy generation and use); the convenience of the public, which benefits in many ways from knowledge of anticipated changes in weather (especially temperature and precipitation); and the broad and complex needs of the Department of Defense for weather information that could affect military operations. Theoretical Advances Required All forecast models, large-scale or small-scale, require some representation of the effect of motions on a scale too small to be represented explicitly in the model. The most important example of this "parameterization" problem concerns the effect of convective clouds. One cloud of
30 this type can differ noticeably from another. Furthermore, the basic equation for cloud processes extends from the individual drops and ice particles to the larger-scale motion fields that may be concentrating the supply of water vapor in the convective region. Slow advances in solving this problem may be expected, especially from the detailed pictures of cloud motion that will be provided by new ground-based systems such as Doppler radar and wind profiler systems. Laboratory Advances Required In ground-based laboratory studies of weather phenomena, the primary needs are for studies of the microphysical processes that occur in clouds. Such studies will lead to a better understanding of heat release and formation of precipitation, which in turn will improve understanding of scale-to-scale interaction. Additionally, these studies will lead to improvement in the ability to measure remotely the relevant properties of clouds. Field Measurements Advancements in field measurements require a composite system that takes advantage of both space-borne and ground-based systems. For example, greatly improved information on mesoscale atmospheric structure will become available through the integration of satellite cloud-type and sounding information with wind and sounding information from ground-based profilers. Automated surface observations in combination with Doppler radar and satellite data will improve our ability to diagnose severe and tornadic storms. Ground-based profilers, Doppler radar, and automated data-collection platforms will have a major impact on weather research and services of the future. However, observational studies of cloud and precipitation processes are needed. These will require a combination of ground-based remote sensors and airborne in-situ remote sensors.
3l Space-Borne System Advances Space-borne system advances needed in the field of weather can be divided into three aspects: l. Increased accuracy and vertical resolution of satellite-measured profiles of temperature and moisture are needed. Present operational systems are not competitive with the conventional radiosonde, especially in the measurement of convective instability (the latent instability of the atmosphere in the presence of moist-air convection). 2. There should be a greater exploitation of microwave sensors, not only to provide temperature and water vapor measurements in cloudy areas, but also to increase the accuracy of measurements of precipitation and ground wetness from satellites. 3. Direct measurement of wind by satellite-borne Doppler lidar would greatly enhance the accuracy of large-scale meteorological analyses. In midlatitudes, winds are now derived by starting with infrared temperature profiles and then using the geostrophic assumption. In typical midlatitude situations, a temperature measurement with a lÂ°C error is easily matched in information content by a wind measurement with an error of 3.5 m/s (Lorenz, l983). But accuracies of lÂ°C or better are unlikely to be achieved operationally in the near future. On the other hand, Doppler lidar can measure winds directly with an error of l m/s and hence would be much more valuable for wind measurement. At low latitudes, the temperature measurement error must decrease significantly to yield good wind information (see, for example, Phillips, l983). New and different sensing systems and spacecraft will be required to make the needed measurements. For example, a possible observing system might include the following: â¢ Spacecraft in high-inclination (polar) low earth orbit to provide data advanced over that provided by TIROS N (one of the satellites in the National Weather Service operational system) â¢ Spacecraft in low-inclination (tropical) low earth orbit especially for the measurement of winds and precipitation
32 â¢ Spacecraft in geostationary orbit carrying imaging and profiling systems using microwave channels as well as infrared, and thus providing profiling capabilities through clouds Space platforms or space stations may be useful for some of these sensor systems, because they may require large amounts of power (more than l kW for a satellite-borne lidar designed to measure winds), their weight may be high, and they may need large antennas (for active or passive microwave sensors of adequate spatial resolution). The operational payloads at low earth orbit and geosynchronous orbit that will be required to monitor the atmosphere adequately will be considerably larger and more expensive than existing systems. It seems probable, therefore, that if manned space stations were placed in low earth orbit for other purposes, it would be cost-effective to use the stations to update sensors or other system components, to repair and/or retrieve the payloads, and to construct larger structures for transfer to geostationary orbit. Technologies Needed Currently, in the lowest levels of the atmosphere over land, and in regions of clouds, satellite sounding systems are not able to define the three-dimensional fields of wind, temperature, and humidity with the accuracy desired for numerical weather prediction. Therefore, for the present, the satellite observing systems should be complemented over land by continuous, automatic, ground-based profiler systems, which are able to measure the desired fields in these regions with the necessary accuracy (Hogg and coauthors, l983). In the future, an improved global wind-measuring system is needed to measure the tropospheric wind field. This is particularly necessary in the tropics, because in that region winds derived from temperature profiles are inaccurate and hence of little use. Infrared Doppler lidar offers a means of achieving a greatly improved wind-measuring system. Improved microwave radiometry on low-earth-orbit satellites is needed to enhance satellite temperature and humidity profiling capabilities under cloudy conditions. A method of measuring rainfall rate from satellites needs to be developed and tested. No generally accepted method of achieving this has yet been identified.
33 A high-spatial-resolution microwave sounding and precipitation monitoring system needs to be developed for use on geostationary-orbit satellites. This will require a large microwave antenna system, for which some concepts already exist. CLIMATE Introduction Climate is usually defined as the weather that occurs at a particular locale over an extended period of time. For the purposes of this report, a 30-day period is used as a lower limit to distinguish climate from weather. The Sahelian drought and the oil embargoes of the l970s focused worldwide attention on the effects of climate on our utilization of scarce resources. In l979, recognizing the critical role of climate in societal and economic affairs, Congress enacted the National Climate Program Act. More recently, a World Climate Program has been established jointly by the WMO, the ICSU, and the United Nations Environment Program (UNEP). Improved forecasts of climate would permit more efficient use of scarce resources. For example, they would contribute to more effective planning of irrigation, more cost-effective distribution of fuels, and better management of commodity inventories. Forecasting large-scale climate depends on progress in understanding a range of phenomena, such as stratospheric ozone, cloud/radiation processes, ocean temperature, ocean/air interface conditions, and ocean ice cover. Many studies of climate and of the advances required to predict it have been done by the National Research Council (U.S. Committee for the Global Atmospheric Research Program, l975a,b) and others (Rasmusson and Carpenter, l982; National Center for Atmospheric Research, l980; and National Aeronautics and Space Administration, l977). These studies led to the Panel's suggestions for field measurements. Field Measurements Requirements for field measurements are well defined by the U.S. National Climate Program Plan and by the World
34 Climate Program mentioned above. Long-term (greater than l0 years), stable, reliable measurements are needed with high precision. In some cases, absolute accuracy is less important than are reliable measurements of trends, cycles, rates of change, or spatial gradients. Measurements are needed for three reasons: (l) to monitor changing climate (what is happening); (2) to study ocean and atmospheric processes that affect climate (why climate changes); and (3) to guide and test climate model experiments (how climate might change in the future). Advances in measurements for climate purposes are considered below for the following classes of observations: earth and solar radiation, internal atmospheric parameters (e.g., clouds, precipitation), ocean parameters (e.g., energy transport, biochemistry), ice and snow, and aerosols and gases. Ground-based and space-based contributions to the field measurements are discussed for each of these classes of observations. Earth and solar radiation measurements are important in studying the energetics of the atmosphere. Net solar radiation has been found to correlate very closely with evaporation from plants and crops; reliable radiation data could improve crop models. However, radiation measurements are sparse over most of the continents and are essentially absent over the oceans. Data sets of internal atmospheric processes for periods of time approaching l00 years are available from weather stations. However, these data sets are available only over land areas. Global data are needed. Regarding oceanic data, in-situ measurements will be needed for subsurface currents, heat flux, salinity, and chemical composition for studies of global geochemical cycles. For ice and snow, ground-based measurements will be needed for snow depth and snow-water equivalent. Passive and active systems are being investigated for deriving water-equivalent snow depth. For gases and aerosols, ground-based measurements and aircraft and balloon measurements will continue to be needed for initial development of sensors and techniques and for verification of satellite measurements, as well as to aid in fundamental research. Earth and solar radiation measurements at the "top" and the "bottom" of the atmosphere are very important. On the
35 climatic time scale, circulations in the oceans and the atmosphere are driven by thermal forces due primarily to radiation from the earth and the sun. At the top of the atmosphere, satellite measurements of the net energy exchange between earth and space and its variation are essential, and are being made. Measurements by satellites of the solar energy output must be made by pointing at or tracking across the sun. Recent solar irradiance measurements from Nimbus 7 and from the Solar Maximum Mission spacecraft identified distinct episodic variations of solar output on scales of days; the variations are highly correlated with visible sunspots. The earth radiation budgets to be measured from satellites should place particular emphasis on the tropical regions (latitudes closer to the equator than 30Â°). The measurements are required at a resolution of 250 by 250 km, with sampling several times per day. The radiation budget and climatological wind and precipitation requirements generate demands for data in the tropical regions and may make a low-inclination orbit useful. For climate, certain satellite measurements (e.g., the Earth Radiation Budget Experiment [ERBE] and measurement of the sun's radiation in the Solar Maximum Mission) should be continued through the coming years. In addition, the atmospheric parameters of winds, atmospheric moisture, and atmospheric temperature, in addition to clouds and precipitation, need to be measured from satellites. It is particularly important to obtain data on atmospheric precipitation patterns and cloudiness (VonderHaar and coauthors, l982; National Center for Atmospheric Research, l980; National Aeronautics and Space Administration, l977), especially over ocean areas. Understanding the influence of the oceans on climate is key to improving the entire state of knowledge regarding climate. Of special importance is the need to understand the transport of heat toward the poles and the influence on atmospheric dynamics of vertical exchange of heat and moisture at the air/sea interface. Finally, there is speculation that relationships exist between El Nino oceanic warmings, large-scale atmospheric dynamics (southern oscillation) and upper-atmospheric flow over North America (Rasmussen and Carpenter, l982). The requirements for modeling and empirical studies are documented in several studies, such as the study of the
36 National Center for Atmospheric Research (l980) and the Proposed NASA Contribution to the Climate Program (National Aeronautics and Space Administration, l977). Major ocean climate experiments are being planned for the late l980s through the l990s. Space-borne measurements are expected to play major roles in covering the remote ocean areas. These experiments, if successful, are likely to lead to new and extensive ocean-monitoring requirements. The earth's cryosphere is thought to be an interactive indicator of the earth's climate, but in order for the subject to be explored fully it is necessary to know the extent of continental snow cover, the extent of polar icepacks, and polar sea-ice concentrations. Because these areas are often heavily cloud-covered, microwave measurements that can penetrate the clouds are valuable. Even though snow and ice measurements so far have employed spatial resolution on the order of tens of kilometers, they have been useful for research and for some operational needs. Higher resolution is required, however, for future improvements in understandingâand perhaps monitoringâclimate change. Possible Role of a Space Platform or a Space Station in Climate Research and Applications As noted earlier, a climate measurement program requires long-term, stable, and reliable measurements. A space platform implies a long-term effort and thus is consonant with climate objectives. Several possible uses of a platform for climate research and applications are specified below. Intersatellite Calibration Facility Because climate measurements require very careful attention to time and space sampling, systems of satellites are now being planned for climate purposes. The International Satellite Cloud Climatology Project (gathering data from l983 through l987) proposes to use six satellites (five geostationary, one sun synchronous) to obtain required information about clouds. During l984 through l986, two or three satellites (one with a 57Â° orbit and the others sun synchronous) are planned to be used in the ERBE project to measure the energy exchange between earth and space and to monitor direct solar energy
37 output. Such systems of satellites are essential to meet climate (and some weather) requirements. Often such satellite systems may include some non-U.S. satellites. In such cases, there is a special need for each satellite system to be normalized so that calibration shifts of individual sensors, should they occur, do not invalidate the overall system. A sensor package on board a space station would serve as an excellent calibration standard because it could be routinely tested in space or even returned to earth if necessary. The sensors' footprints on the earth would have to be matched, and a space platform (for example, on an orbit inclined at 28.5Â°) would have to underfly free-flying satellites in the system to permit intercalibration at each encounter. Low Signal-Above-Background Measurement Some climate-related measurements, such as those for very detailed winds, certain volcanic gases and aerosols, and low-level moisture, have a very low signal-above- background level. To detect these fine-scale, yet important, climate features, special instruments (e.g., lidars) may be needed. Power and other requirements for these sensors may preclude their use on a free-flyer, which would perhaps be too small to support such sensors; thus, a space platform may be the optimum satellite for this purpose. Normally, global coverage would be required for climate modeling and monitoring. However, certain important parameters such as tropical winds could be measured from a low-inclination platform. Assembly of Large Antennas Climate research could benefit from higher-resolution microwave measurements. This will call for the deployment in space of antennas with diameters up to l0 m in low earth orbit, and much larger in geostationary orbit. Role of Man in Space for Climate Research and Applications In general, the Panel finds no requirements for human observers in space for climate research or for
38 applications of climate-related remote sensing. If a manned observatory is planned for solar physics studies, certain climate-related measurements of total and spectral energy from the sun might be included. Of course, the accuracy and precision of the measurements would have to match or exceed those from unmanned sites. CONCLUSIONS The Panel has focused on possible evolutions in environmental observations during the l980s and examined the role that a space platform or a space station might play in future developments. It is generally concluded that a space station offers the potential for several new activities in space, including: Combining a large number of sensors for simultaneous observation of many species in the atmosphere The ability to recalibrate instruments frequently and to use these instruments to intercalibrate satellites The possibility of refurbishing and repairing instruments and of maintaining cooled detectors for an extended period The introduction of new facilities such as lidar or major microwave observatories in space Advances in technology that should be explored are: Development of remote-measurement techniques for OH and N02 Techniques for handling a multiple-data-stream mode, including onboard processing Larger space-borne power systems Development of tropospheric remote sensing instruments Development of a global wind-measuring system Improved microwave radiometry for low-earth-orbit satellites Development of a method for measuring rainfall from satellites Development of a high-spatial-resolution microwave sounding system
39 In regard to orbit, while low-inclination low earth orbits are useful, especially for observing tropical weather and climate, by far the most important orbits for environmental observations are low-altitude near-polar orbits (for rapid-response, synoptic weather forecasting) and geostationary orbits (for environmental observations and for atmospheric sounding). If a space platform having a number of sensors is contemplated, it should be placed in a low-altitude near-polar orbit. The general conclusion regarding the role of man in space is that human presence could be useful on a periodic rather than on a continuous basis. This conclusion, by necessity, is based on a limited examination. The possibilities of a more creative and innovative role for man in space should be examined in more depth. REFERENCES Hogg, D. C., M. T. Decker, F. 0. Guiraud, K. B. Earnshaw, D. A.Merritt, K. P. Moran, W. B. Sweezy, R. G. Strauch, E. R. Westwater, C. G. Little. l983. An automatic profiler of the temperature, wind and humidity in the troposphere. Journal of Climate and Applied Meteorology 22(5):807-83l. Keafer, L. S., Jr., ed. l982. Tropospheric Passive Remote Sensing. Proceedings of a workshop held July 20-23, l98l. NASA Conference Publication 2237. Accession No. 82N-26637. Springfield, Va.: National Technical Information Service. Levine, J. S., and F. Allario. 1982. The global troposphere: biogeochemical cycles, chemistry, and remote sensing. Pp. 263-306 in Environmental Monitoring and Assessment, Vol. l. Dordrecht, Holland/Boston, Mass.: D. Reidel. Lorenz, E. l983. Atmospheric prediction experiments with a large numerical model. Tellus 34:505-5l7. National Aeronautics and Space Administration. l979. Shuttle Atmospheric Lidar Research Program. NASA Special Publication 433. Washington, D.C.
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