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.
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