ASSESSMENT OF NASA'S MISSION TO PLANET EARTH/EARTH OBSERVING SYSTEM (MTPE/EOS)
Working Group Participation
Gregory Canavan, Chairman
Eric J. Barron
Edward A. Frieman
Richard M. Goody
Noel W. Hinners
Jerry D. Mahlman
John H. McElroy
Berrien Moore III
S. Ichtiaque Rasool
Designated Federal Liaison: Chris Scolese
Rapporteur: Frank Eden
WORKING GROUP SUMMARY
Gregory Canavan, Chairman
EOS's program structure and science have been significantly improved. Its research is thoroughly peer reviewed by excellent, independent academic science teams with strong inputs from a wide range of respected scientists. The results of those reviews are routinely communicated to and acted on by the appropriate levels of the National Aeronautics and Space Administration (NASA) and the U.S. Global Change Research Program (USGCRP).
EOS provides unique information for the execution of required global assessments. Current sensors and platforms are appropriate and efficient. EOS sensors correctly reflect the Earth system science priorities that can be measured effectively with existing sensors and give proper emphasis to the development of sensors for other important phenomena. Areas in which change is needed are recognized and are being addressed. One is the need for properly documenting global change. Current sensors reflect an earlier emphasis on process studies. A rigorous dynamic calibration and validation program is essential for maintaining the dynamic continuity of critical long-term measurements through successive generations of sensors. Fortunately, EOS sensors are designed for high calibration.
EOS is properly configured for science and programmatic resilience. NASA has significantly increased opportunities for the introduction of advanced technology through experiments such as Lewis and Clark and through continuing science programs such as the Earth System Science Pathfinder (ESSP). It has become increasingly open to the infusion of technology from the Department of Defense (DoD) and industrial programs, which have significantly strengthened EOS.
Observing system priorities remain consistent with those of the USGCRP and the four MTPE science areas, which require ground and in situ measurements. Significant, rapid change has required and produced significant learning, but the broad, continuous EOS data sets remain relevant. The need for new measurements (e.g., tropospheric wind and aerosols, soil moisture) has become apparent and has stimulated productive thought on new means to measure them, perhaps from small satellites. It has also stimulated thought on new ways to perform key measurements such as lightweight synthetic aperture radars (SARs), hyperspectral sensors, and tropospheric chemistry sensors.
The current range of scientific uncertainties makes EOS's broad range of measurements relevant--particularly in that its sensors emphasize the validation, calibration, and continuity required for the detection of subtle climate signals. EOS supports a wide variety of societally relevant assessment programs and applications such as deforestation, agriculture, and water resources and quality. It addresses these priorities in cooperation with ground-based and in situ sensors. Current efforts include a productive mix of space, in situ, and ground measurements through a proper blend of agency contributions. The detailed correlation of space sensor capabilities with current science area priorities could be usefully addressed by a longer study.
Technological opportunities are being pursued aggressively. There is a sound process for the design of sensors with the performance and calibration required for measurements of the quality required for global change research. That process proceeds from requirements, through technology and trades, to sensor designs, in which size is properly seen as a dependent variable. EOS sensors use best current technologies and calibration methods--including those of DoD--to optimize performance. EOS is now the principal driver of sensor technology and research. Although it is fairly new and not fully activated, there is now a process for the incorporation of other emerging technologies, as well as established vehicles for the importation of technologies developed for other purposes by DoD and industry. There is adequate launch capability in existence or development for satellites of all sizes. All are affordable, although the cost per kilogram of payload is about a factor of three higher for small launchers than for launchers in the Delta class, as is designing spacecraft for compatibility with several launch vehicles to reduce sensitivity to launch losses at modest cost and performance penalties.
We can now build capable satellites of any desired size effectively; their performance domains are evolving rapidly. We now understand better when it is possible and appropriate to distribute sensors over many satellites. It is also better understood when various technologies should be used (e.g., technologies developed by DoD appear applicable to laser aerosol measurements, but not to spectral measurements, for which they currently lack calibration). It is also understood how efforts such as the New Millennium Program (NMP) can address bus costs, but not usefully substitute for operational buses or reduce system costs, which NMP does not address.
Small satellites promise low spacecraft costs and short schedules--typically one to two years from conception to flight. They provide mission and programmatic flexibility, which are important in stimulating innovation. Formation flying may also enable their use in replacing failed instruments or in maintaining dynamic continuity of measurements when introducing new sensors. Small satellites are currently best suited for focused missions of narrow scope. They are not universally applicable to the current generation of EOS sensors, many of which are too heavy or too large for small satellites. Life- cycle costs (sensors, satellites, launch, mission operations, and data acquisition) are not necessarily reduced by replacing the current multisensor medium-sized satellites with many small satellites for the deployment of a full suite of high-quality, calibrated sensors. Advances in technology, such as may come from the ESSP, NMP, and other sources, might alter this conclusion within the next few decades.
Data continuity is essential for meaningful scientific results. Space programs such as NASA's Landsat have successfully produced long-term records of key parameters, although not with the calibration desired by the climate research community. EOS will fly well-calibrated radiation, tropospheric water vapor, and aerosol sensors, as well as a series of Moderate Resolution Imaging Spectroradiometer (MODIS) instruments for the cloud feedback studies suggested by the Marshall Institute and others. As the latter have, long-term programmatic stability is essential for the success of these studies. To extend the studies of physical climate effects to global change, which is more complex, requires measurements over oceans and land--hence their inclusion in EOS. It is unlikely that a narrowly focused study would provide satisfactory long-term answers to these questions.
Convergence opportunities offer the promise of reduced overlap, reduced cost, and improved science through NASA, National Oceanic and Atmospheric Administration (NOAA), and DoD cooperation on weather and climate satellites. There are significant institutional barriers and technical issues that could impede such convergence, but the payoff is so great that it justifies extensive study. If operational instruments were calibrated to research standards, a wide community of users would benefit. Much the same can be said for multiuse (science, operational, military, commercial, and international) missions on common platforms. Such developments have been strongly resisted because of cost, interference, and regulatory concerns, although these arguments are becoming less relevant while the potential savings are increasing.
There is a long, successful history of international cooperation in Earth observation. Many nations are providing satellites and sensors that form an essential part of the MTPE program. European and Japanese sensors will fly on NASA satellites and vice versa. Data exchange agreements are being implemented among these partners and others to maximize their value to the overall community. Many of EOS's sensors are provided by international partners; they are coordinated through EOS-ESA (European Space Agency) sensor discussions; and Europe, Japan, and Canada will provide EOS ground segments. In operational systems, NOAA polar orbiters carry important donated foreign instruments, and Europe's EUMETSAT will assume responsibility for one of NOAA's traditional satellite flights near the turn of the century. When one of the U.S. Geostationary Operational Environmental Satellite (GOES) geostationary weather satellites failed, EUMETSAT provided one of its satellites to prevent data loss for the critical Atlantic seaboard.
These international arrangements are voluntary and exercised primarily through the Committee on Earth Observation Satellites (CEOS). Reliance on such mechanisms leaves the United States with no fall-back position in the event of default, although U.S. reliability has been most in question of late because of issues such as Topex- Poseidon. It would be useful to isolate EOS from current political issues. At present, the United States has limited ability to affect these arrangements because of the inability to make multiyear commitments. There could be significant benefits from being able to address reliability by entering into multiyear commitments on satellites, sensors, and global observing systems.
Innovative approaches to data collection and management may offer significant savings. Data purchases still appear attractive and useful, despite recent experiences with SeaWIFS. However, the government would have to enter into long-term contracts to stabilize purchases sufficiently to secure the interest of industry. Commercial activities and opportunities for sensors on commercial constellations such as Teledesic and IRIDIUM are uncertain. There has been only limited contact and discussion, and industry reception to date has been characterized as not very positive. That is understandable. The market is very uncertain. Only the upper limit of the estimates of its magnitude would approach the cash flows involved in those systems; anything less would be viewed as a hindrance to their rapid deployment. In any case, communication satellites do not use polar sun-synchronous orbits; the radiometric correction of data taken from their orbits does not appear feasible.
Applications of EOS data are much greater than those of previous Earth sensing satellites. For agriculture, Landsat-7 offers a major improvement in the measurement of crops, and the AM and PM (morning and afternoon equator crossing) platforms will significantly improve measurements of vegetation and moisture. For land use, Landsat-7 will greatly improve surveys of biodiversity, and AM will improve the precision of maps. For seismology, AM will document changes in land surface and volcanism. For hydrology, radars will improve topography and El Ni?o/Southern Oscillation measurements; lasers will measure ice; and AM and PM will significantly improve understanding of cloud dynamics and cover. For mapping, AM will provide digital elevation; lasers will give ice and land elevation. For national security, Landsat-7 will greatly improve the type of global surveillance provided for the Gulf War; AM will improve map resolution; and PM will give the moisture measurements needed for force mobility analyses. All of these improvements will be of significance for both civil and commercial applications.
Program Impact Issues
Restructuring has protected the EOS program and increased its resilience, but that process has reached its limit. Significant reductions in annual or aggregate budgets or imposed constraints on technical options could result in elimination of key sensors or platforms, slippage of schedules, loss of continuity in data sets, or elimination of the mechanisms for promoting the innovation needed for downstream cost reductions and science improvements. A premature shift to small platforms could eliminate key measurements.
Summary EOS's science and program are valuable, unique, and resilient. It would be appropriate to reduce its reviews to regular but less frequent intervals. Its space observation program has appropriate balance internally, but needs to be balanced with ground and in situ measurement across all of the USGCRP priorities. EOS priorities are evolving and open to technological innovation. Its sensors are well designed and calibrated. Given long-term program stability, they should be able to provide the quality of continuous measurements of radiation, vapor, aerosol, and cloud feedback necessary to understand and document climate change.
EOS is open to the introduction of technology from research, DoD, and commerce. Adequate launch and fabrication capability exists for satellites of all sizes. Small satellites offer flexibility and rapid innovation--at a penalty in cost. However, it should be possible to use them effectively to perform rapid tests of new sensors for key parameters such as tropospheric winds, aerosols, and soil moisture, among others.
Convergence offers significant advantages and savings domestically and internationally. Impediments to the convergence of domestic programs, which are largely institutional, could profit from more careful study and definition. International collaboration has a long, successful history. Current impediments, which are produced in part by the voluntary nature of these collaborations, could be improved by multiyear commitments. EOS data will have significantly greater value for civil, commercial, and defense applications than the data from previous lower-resolution sensors. These applications alone could justify maintaining EOS's schedule. However, although the EOS program remains resilient, it is now stretched to its limits. Further reductions or constraints could reduce its technical capabilities and delay or eliminate those advances.