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Review of NASA’s Solid-Earth Science Strategy
observations were subject to limitations: (1) the 5.6-centimeter wavelength (C-band) of the ERS radars resulted in the radar coherence in vegetated areas decreasing rapidly with time; and (2) competing scheduling priorities for the ERS satellites resulted in the acquisition of images needed to observe crustal strain accumulation only in limited areas and at limited times.
SESWG Recommendations—Surface Deformation
Immediate (1–5 years): A single dedicated InSAR satellite operating at L-band, with left/right-looking capability and weekly access to anywhere on the globe. Such a mission should include precise orbit determination and ionospheric correction capabilities. This mission should achieve accuracies of 1 mm/yr surface displacement over 50 km horizontal extents in selected areas. Displacement maps should cover 100-km-wide swaths. Continuous ground GPS observations will provide important complementary information.
Near Term (5–10 years): A constellation of InSAR satellites capable of producing deformation maps at nearly daily intervals. Maps should extend several hundred kilometers in swath width and provide full vector surface displacements at accuracies of submillimeter per year over 100-km spatial extents and 1-m spatial resolution. Complementary ground and seafloor geodetic observations should continue.
Long term (10–25 years): Hourly global access from a constellation of InSAR satellites in low earth or geosynchronous orbits. There should be an increase in the density of continuous ground and seafloor geodetic observations.
SOURCE: National Aeronautics and Space Administration, Living on a Restless Planet, Solid Earth Science Working Group Report, Pasadena, Calif., pp. 31-32, 2002, <http://solidearth.jpl.nasa.gov/seswg.html>.
Scientific and Societal Benefits of the SESWG Recommendations
Understanding of the processes governing deformation of the earth’s surface at plate-boundary regions and the related problem of the physics of earthquakes is undergoing a revolution. Major advances have been made possible by the confluence of new observations of surface deformation using space geodesy, new theories of stress transfer and earthquake interaction in fault systems, and rapid growth in computational capability. In addition, the deformation fields before, during, and after several recent, large earthquakes have been characterized unusually well via both space geodesy and strong-ground-motion seismology. These observations have made it possible to constrain the kinematics of earthquake sources and the dynamics of stress and strain transfer after earthquakes in ways that were impossible previously.
InSAR has also influenced volcanology by improving measurements of ground deformation in systems ranging from small composite cones to the largest calderas. Measurements of volcano deformation have been available for some time, but before InSAR, they were time
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