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Review of NASA’s Solid-Earth Science Strategy Executive Summary The centerpiece of the Solid-Earth Science Working Group’s (SESWG’s) strategic vision for the National Aeronautics and Space Administration (NASA) is an ambitious program of continuous measurements of the changing surface of the earth and its external fields. As explained in the SESWG report Living on a Restless Planet,1 the justification of and motivation for this vision are the scientific and societal benefits that will be derived from NASA’s undertaking this program and its unique role in mitigating a broad range of natural hazards. In this report we review the recommendations in the SESWG report and answer the questions posed by Dr. Ghassem Asrar, associate administrator of NASA’s Office of Earth Science: Are the priorities of the report consistent with national priorities in the solid-earth sciences, as laid out in the strategic plans of relevant federal agencies and interagency organizations? Does the report include all the major research foci for which NASA can make a unique contribution? Consistency with National Priorities in the Solid-Earth Sciences We find the priorities identified in the SESWG report to be consistent with the priorities of U.S. federal science agencies and organizations that sponsor significant programs in basic or applied solid-earth science. Implementing the recommended observational strategies in a timely manner will be important for major earth-science initiatives in many federal agencies, including: studying the structure, composition, and evolution of the solid earth (EarthScope, NASA, National Science Foundation [NSF], U.S. Geological Survey [USGS], Smithsonian); studying the dynamics at the interfaces of earth systems (NSF, NASA, Climate Change Science Program [CCSP], National Oceanic and Atmospheric Administration [NOAA]); studying the processes that cause natural hazards (NSF, NASA, USGS); measuring motions of the earth’s surface (NASA, NOAA, NSF); analyzing watersheds, hydrological fluxes, or fluid flow in reservoirs (NOAA, USGS, Department of Energy [DOE]); and characterizing, monitoring, or managing the earth’s surface (USGS, NSF, Environmental Protection Agency [EPA], U.S. Department of Agriculture [USDA]). 1 National Aeronautics and Space Administration, Living on a Restless Planet, Solid Earth Science Working Group Report, Pasadena, Calif., 63 pp., 2002, <http://solidearth.jpl.nasa.gov/seswg.html>.
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Review of NASA’s Solid-Earth Science Strategy Inclusiveness of Major Research Foci to Which NASA Can Make a Unique Contribution The SESWG report identifies observational strategies in five primary areas: surface deformation, high-resolution topography, surface properties using imaging spectroscopy, variability of the earth’s magnetic field, and variability of the earth’s gravity field. We believe that these are the major solid-earth research themes for which NASA can make significant and unique contributions given reasonable assumptions regarding actual and proposed satellite-based observing systems. No other agency has the experience in developing, building, and launching instruments in these research areas, although many will use the data in their own applications. NASA’s experience with IT will also be important for analyzing the large volumes of data produced by continuous, global monitoring and for disseminating information to the community quickly. Analysis of SESWG Recommendations The SESWG report makes recommendations for implementing each of the observational strategies in the short term (1–5 years), near term (5–10 years), and long term (10–25 years). Our analysis is as follows: Surface Deformation. Interferometric synthetic aperture radar (InSAR) measurements are leading to significant advances in quantifying processes that deform the surface of the earth—including earthquakes, subsidence, the movement of magma beneath volcanoes, and the extraction of fluids—and their associated hazards. InSAR is also a key component of a number of agency programs, such as the USGS hazards mitigation program and EarthScope. We strongly endorse the view expressed in the SESWG report that the new space mission of highest priority for solid-earth science is the launch of a satellite dedicated to L-band InSAR measurements of the land surface within the next five years. However, we suggest that technological improvements to expand InSAR capabilities and/or reduce costs be considered when planning for future space-based missions. High-Resolution Topography. We support the goals of releasing 30-meter data from the Shuttle Radar Topography Mission, acquiring global 2- to 5-meter-resolution land topography data in the near term, and developing the technology to collect targeted 1-meter-resolution data in the long term. Use of these data would advance studies of tectonic, geomorphic, climatic, and biotic processes and would improve the detection and forecasting of geologic hazards, as long as challenges in analyzing and distributing large volumes of data in near real time can be overcome. Advances in understanding ocean floor processes and mantle dynamics could be expected from the acquisition and use of 5-kilometer resolution bathymetric data, although collection of such data is not a stated goal of the SESWG report. Variability of the Earth’s Magnetic Field. We endorse the SESWG near- and long-term goals of collecting enhanced observations from increasingly dense constellations of satellites in coordinated orbits. Such instrument configurations are needed to separate out large-scale temporal and spatial variations in the external field, to study the effects of dynamo activity in the earth’s liquid outer core and the electrical properties of the mantle, and to evaluate the impact of space weather on communications and satellite observations. Because geomagnetic missions are currently being flown by other countries, the SESWG report’s immediate goal of analyzing observations from current missions is reasonable. The upcoming European Space Agency (ESA) Swarm mission would satisfy the SESWG report’s 5–10 year goal for a small constellation of satellites, provided that NASA reaches a formal agreement with ESA for U.S. researchers to have timely and affordable access to Swarm data. To satisfy longer term goals NASA will have to initiate planning for larger constellations of satellites, exploiting opportunities for collaboration with other countries. This strategy should advance the science as well as help maintain U.S. expertise in geomagnetic instrument development, modeling, and analysis. Variability of the Earth’s Gravity Field. NASA’s current time-variable gravity mission—Gravity Recovery and Climate Experiment (GRACE)—is functioning according to design, and we endorse the SESWG goal of spending the next five years using the data to study geophysical
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Review of NASA’s Solid-Earth Science Strategy processes such as postglacial rebound. ESA’s Gravity Field and Steady-State Ocean Circulation Mission (GOCE) satellite will provide experience with satellite gravity gradiometry, and the proposed near-term NASA mission would test satellite-to-satellite interferometry. A careful analysis of these and perhaps other approaches will help NASA choose the most appropriate gravity measurement technology to replace GRACE in the long term. Surface Properties Using Imaging Spectroscopy. We support implementation of the stated and implied SESWG recommendations, including continuation of the Airborne Visible/ Infrared Imaging Spectrometer (AVIRIS) and development of a hyperspectral (less than 10-nanometer bandwidth) visible-near-infrared spaceborne instrument. Rather than simply refining existing techniques, new sensor technologies will be required to enable identification of minerals, rocks, and soils and to monitor landscape change, volcanism, tectonics, and ice dynamics. In addition to airborne and spaceborne hyperspectral capabilities, continued operation of multispectral instruments would help meet a number of scientific objectives, although multispectral equivalent products could be derived from hyperspectral data if choices must be made. Overall, we find that the observational strategies outlined in the SESWG report would take advantage of NASA’s skills in sensor development and yield important data for addressing major earth-science challenges. Equally important to the success of NASA’s solid-earth program will be the analysis of data from existing and planned instruments flown by NASA and space agencies in other countries, especially to meet the gravity and magnetics scientific objectives. Although adjustments might be necessary as new technology is developed, we believe that the observational strategies provide a sound basis for guiding NASA’s solid-earth science program in the coming decades.
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