1. high-resolution topography

  2. variability of the earth’s magnetic field

  3. variability of the earth’s gravity field and

  4. imaging spectroscopy of the earth’s changing surface.2

We note that imaging spectroscopy is the most practical way to measure certain surface properties remotely—it is not a fundamental scientific measurement. For consistency with the other observational strategies, we discuss it under the title “surface properties using imaging spectroscopy.”

For each of the observational strategies, the SESWG report makes specific recommendations for implementation at short-term (1–5 years), near-term (5–10 years), and long-term (10–25 years) time scales. In addition to these five observational strategies, the report makes recommendations regarding space geodetic networks and the International Terrestrial Reference Frame, as well as promising techniques and observations. In general, priorities are not assigned to the recommendations, with the important exception that the launching of a satellite dedicated to interferometric synthetic aperture radar (InSAR) measurements of the land surface is identified as the single highest priority for NASA’s solid-earth science program. The report concludes with a description of elements that complement the recommended observational strategy, including research and analysis, information systems, technology development, supporting framework, and education.


Our report covers the five observational strategies highlighted by the SESWG report and the specific recommendations related to each strategy. For each of the strategies, we

  • provide a brief overview of its background;

  • repeat the immediate, near-term, and long-term recommendations of the SESWG report;

  • describe the scientific and societal benefits that would accrue from proceeding as recommended;

  • summarize the relationship of the recommendations to national priorities in solid-earth science laid out in strategic plans of relevant federal agencies and interagency organizations (summarized and referenced in Appendix A);

  • analyze whether the strategy as defined identifies ways in which NASA can make a unique contribution;

  • analyze the strengths and weaknesses of the recommendations and highlight key technical challenges and advances that will be necessary to implement the strategies as described; and

  • summarize our analysis.

After analyzing the observational strategies, we conclude with a summary of our evaluation, highlighting those aspects of the recommendations in the SESWG report that are of highest priority.

We note at the outset that there are aspects of the SESWG report that we have chosen not to review. For example, we do not evaluate explicitly the validity of the six broad scientific challenges that motivated the proposed observational strategies. Our reasoning is that these scientific challenges reflect classic, major issues in earth science.3 Although considerable and


National Aeronautics and Space Administration, Living on a Restless Planet, Solid Earth Science Working Group Report, Pasadena, Calif., p. 29, 2002, <http://solidearth.jpl.nasa.gov/seswg.html>.


For example, the scientific themes recommended to guide NASA’s solid-earth program a decade ago were similar in scope, although somewhat different in focus, to the SESWG scientific challenges. They

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