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2 Analysis of SESWG Recommendations
Pages 9-30

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From page 9...
... Surface deformation that occurs during the interval between the recording of two images results in changes in the radar signal, which can be transformed into a map of ground displacement. The first InSAR mapping of surface deformation associated with earthquakes and volcanoes used observations made by the European Space Agency's (ESA's)
From page 10...
... SESWG Recommendations -- Surface Deformation Immediate (1­5 years) : A single dedicated InSAR satellite operating at L-band, with left/rightlooking capability and weekly access to anywhere on the globe.
From page 11...
... Societal Benefits Measuring surface deformation in regions of active fault systems, volcanoes, and landslides provides data for assessing the risk associated with these phenomena. For example, because volcanic eruptions are typically preceded by surface deformation, InSAR measurements could be used to make short-term predictions of volcanic eruptions.
From page 12...
... Strengths and Weaknesses of the SESWG Recommendations We believe that the immediate-term InSAR mission is correctly identified as the top priority for NASA's solid-earth program and agree that this proposed InSAR mission is timely, coinciding with the PBO component of the EarthScope project plan, of which it is a critical part. Furthermore, this InSAR mission would provide data that are important for understanding many scientific problems related to natural hazards, such as the physics of the earthquake cycle, the physics of magma movement and magma interaction with the upper crust, the mechanics of crustal deformation, and the processes that contribute to temporal changes of surface deformation and mountain building.
From page 13...
... methods. The spatial resolution of topographic data varies, ranging from 30 meters to several kilometers over land areas and averaging about 25 kilometers over the oceans.
From page 14...
... instrument on ICESat provides data at 170-meter intervals along the earth's surface with a 70-meter-diameter footprint.10 "High-resolution topography," as conceived in the SESWG report, would move far beyond what the SRTM and ICESat currently produce, with surface elevation sampled at resolutions approaching 5- to 1-meter horizontal spacing and vertical errors as small as 0.1 meter. SESWG Recommendations -- High-Resolution Topography Immediate (1­5 years)
From page 15...
... · How are active faults manifested in the landscape and what is their relation to plateboundary strain? Although the SESWG report focuses on the land surface, only 0.1 percent of the ocean floor has been surveyed at 100-meter horizontal resolution.
From page 16...
... Detailed bathymetry data can be used to forecast where major underwater volcanic eruptions may occur and where large submarine hydrothermal fields are likely to be found.15 The submarine hot springs support an exotic community of benthic animals whose tissues offer significant potential for pharmaceutical applications. High-resolution bathymetry data could also be used to identify the location of offshore faults which pose significant earthquake or tsunami risk.16 Consistency with National Priorities in the Solid-Earth Sciences All federal agencies that use topographic data could benefit from the proposed satellite program (Appendix A)
From page 17...
... Finally, NASA's experience with remotely operated instruments and data transmission make it well qualified to explore and map the seafloor remotely. Strengths and Weaknesses of the SESWG Recommendations The SESWG report specifies topographic resolution goals of 2 to 5 meters for a first global land survey (the near-term goal)
From page 18...
... Although not a stated goal of the SESWG report, improved bathymetry data would help address scientific questions concerned with plate boundary deformation and mantle processes. The tools that will have to be developed to acquire, process, and analyze high-resolution topographic data sets would also benefit studies of surface processes on other terrestrial planets.
From page 19...
... A constellation of satellites, such as that envisioned in the SESWG report, would overcome this difficulty by providing denser sampling of the external magnetic field and improved accuracy and positioning of the moving instruments. SESWG Recommendations -- Variability of the Earth's Magnetic Field Immediate (1­5 years)
From page 20...
... The highresolution satellite data envisioned in the SESWG report, combined with the use of data assimilation methods, would enable the development of the next generation of geomagnetic field models needed to provide these forecasts. 23 Constable, S.C., and C.G.
From page 21...
... The geomagnetic observations recommended in the SESWG report would complement NSF's priorities to study the structure and composition of the solid earth and dynamics at the interfaces of earth systems. A continued supply of high-quality global satellite measurements is also essential to planetary studies sponsored by other branches of NASA and NSF and by the Smithsonian Institution.
From page 22...
... Summary We endorse the SESWG goal of enhanced measurement of the geomagnetic field through increasingly dense sampling by a constellation of magnetometers, combined with an aggressive program to interpret observations from existing missions. The 5­10 year goals could be satisfied by the ESA Swarm mission provided that NASA takes immediate steps to negotiate a formal data access agreement for U.S.
From page 23...
... SESWG Recommendations -- Variability of the Earth's Gravity Field Immediate (1­5 years) : Monthly estimation to within 10 millimeters of surface water equivalent load at a few hundred kilometers spatial resolution using existing satellites such as GRACE.
From page 24...
... The largest purely solid-earth signal that is expected to be present in the time-varying gravity field is the influence of postglacial rebound.29 Time-variable gravity measurements will help to differentiate between the effects of postglacial rebound and other processes with similar geographical patterns, such as changes in present-day ice sheets. Measurements of postglacial rebound will also lead to significant improvements in the knowledge of mantle rheology and its lateral variations.
From page 25...
... Gravity gradiometry may offer better precision and resolution than GRACE or GOCE for studying shorterwavelength features such as regional tectonics, and laser-interferometric ranging could yield an order-of-magnitude improvement in performance over the microwave differential tracking of GRACE.33 Strengths and Weaknesses of the SESWG Recommendations The study of many different geophysical processes will be significantly advanced by time-variable gravity measurements: the waxing and waning of Antarctic and Greenland ice sheets, continental water storage, sea-level rise (particularly the separation of steric and nonsteric components) , dynamical topography of the oceans and seafloor pressure variations (which induce deformations of the solid earth)
From page 26...
... Imaging-spectroscopy data collected over the solar-reflected and thermalemitted portions of the electromagnetic spectrum are used to identify minerals, rocks and soils, forest tree species, and invasive weeds and to monitor temporally variable phenomena such as landscape and vegetation change, water quality, volcanism, tectonics, and ice dynamics. Imaging spectroscopy was developed in the early 1980s to counter the shortcomings of multispectral-imaging systems such as the Landsat Multispectral Scanner and later the Thematic Mapper, which could not be used to identify materials because of the poor spectral resolution afforded by 4 to 7 spectral bands.35 The modern field of IS was born with the development of instruments that acquired spectral data in hundreds of narrow, registered, contiguous spectral bands.36 NASA has more than three decades of experience collecting high-quality multispectral and hyperspectral data from aircraft and satellites.
From page 27...
... This technology-demonstration mission was designed to map rocks and soils and to monitor small-scale processes -- including vegetation growth, deforestation, land use, erosion and other forms of land degradation, and urbanization -- seasonally and on a global scale. SESWG Recommendations -- Surface Properties Using Imaging Spectroscopy Immediate (1­5 years)
From page 28...
... -- as long as the spectral signal of the pollutant of interest can be differentiated from the spectral signal of the surrounding material. If the SESWG report's recommendations are implemented, the simultaneous high-temporal- and high-spatial-resolution data sets could permit monitoring of particulate plumes from volcanic eruptions, sand storms, dust storms, and toxic materials on a global basis.
From page 29...
... Another weakness of the SESWG report is the lack of specific recommendations for new technology and sensors; most of the discussion refers to refining existing techniques. For example, the thermal imaging spectrometer demonstration project recommended in the near term would require an order of magnitude improvement in spectral resolution.
From page 30...
... communities. Summary We support implementation of the stated and implied SESWG recommendations, including continuation of AVIRIS and development of a hyperspectral (less than 10-nanometer bandwidth)


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