Airborne Geophysics and Precise Positioning Scientific Issues and Future Directions (1995) / Chapter Skim
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2 Scientific Framework
2 Scientific Framework
Pages 29-48
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From page 29... ...
The scientific objectives that are now possible with precise positioning and airborne geophysics can be categorized in the following areas: I interdisciplinary earth science studies; 2.
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From page 30... ...
below, interdisciplinary research topics that can be addressed by airborne geophysics integrated with precise positioning include the following: ice dynamics and sea level rise; erosional processes and landform development; and hydrologic cycle. Ice Dynamics and Sea Level Rise The melting or collapse of large ice sheets is believed to be responsible for rapid sea level rises documented in the geologic record.
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From page 31... ...
Airborne geophysics can provide important constraints on this interdisciplinary problem. Accurate topographic measurements of 1-m resolution on the ice surface and 5-m resolution at its base are necessary to determine the stress state of an ice sheet.
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From page 32... ...
in Texas there are concerns about freshwater levels in the aquifers, as well as deterioration in water quality due to saltwater intrusion and of} contamination in heavily pumped regions. To ensure a clean water supply, it is necessary to adopt an approach that will determine the sources of contaminants and He processes that control their dispersion through the aquifer system.
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From page 33... ...
33 ,,oo,o'Oz~ NW 0000689 NW 0009889 NW 0000889 Two Ul CO Us o so _ _ Ct ~ O c: ._ o _ ._ Ct .
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From page 34... ...
Our understanding of continental geodynamic processes, however, lags greatly behind our knowledge of oceanic lithospheric processes for the following reasons: I In many places the continental lithosphere is deforming in complex ways and not simply by the rigid body rotation that characterizes the oceanic lithosphere; 2.
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From page 35... ...
On regional scales, plate boundaries in both continental and oceanic settings are complex and can best be studied in regions of young and active tectonics. Within oceanic lithosphere, the structural complexity along plate boundaries may be tens of kilometers wide; within continental lithosphere, it may be 2,000 to 3,000 km wide (Argand, 1924; MoInar and Tapponnier, 1975~.
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From page 38... ...
Airborne swath mapping techniques, such as SAR or scanning laser systems, would provide sufficiently accurate measurements of the Earth's surface between the geodetic monuments. Documenting the structure of the crustal blocks that make up a deformation zone also requires detailed understanding of the local geology.
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From page 39... ...
High-accuracy digital topography, with 0.5- to 3.0-m vertical resolution and 30- to 100-m horizontal resolution, is required to resolve deposit boundaries. To mode} volcano inflation, deformation, and pre-eruptive surface modifications, it is necessary to obtain sub-meter geodetic measurements (vertical)
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From page 40... ...
Detailed gravity data have also revealed the complex state of isostatic compensation, and, thus rheology of mountain chains formed by continental collision, although there are still unresolved questions on what kinds of compensation mechanisms are associated with the different types, locations, and histories of plate collision. Finally, high-resolution gravity data over sedimentary basins are needed for an understanding of the thermal and mechanical driving forces that cause basin subsidence.
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From page 41... ...
GPS and new sensor technologies now allow the following features to be identified in sedimentary basins using airborne methods: . structures beneath thick sheets of salt that cannot be easily imaged with seismic techniques because of the velocity structure of salt; faults which may play an important role in oil migration; and structures within the sedimentary column that may trap oil.
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From page 42... ...
The subsurface cavities could be identified with airborne gravity, "radiometry, or electromagnetic measurements; the surface expression of a test site could be determined with accurate topographic mapping. Repeated topographic mapping of a region could also identify postshot subsidence.
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~ . o 40 80 120 1 1 1 160 200 FEET 1 1 Contour interval 2 or 10 feet fIGIlRE 2.3 Topographic map of a large, symmetrical sinkhole produced by an underground nuclear test, northeastern Yucca Flat.
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From page 44... ...
Heights above mean sea level (orthometric heights) are traditionally determined using spirit leveling, which is accurate to a few millimeters over several kilometers of leveling line length.
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From page 45... ...
GLOBAL CHANGE MONITORING AND AIRBORNE GEOPHYSICS Monitoring Ice Sheets and Mountain Glaciers Melting ice has been identified as the major cause of sea level rise. The majority of ice that has the potential to raise sea level is held in the East and West Antarctic ice sheets and the Greenland ice cap, but the mountain glaciers that cover much of Alaska and Patagonia may also contribute to sea level rise (Meter, 1984; Thomas, 1991~.
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From page 46... ...
~ mGal. Airborne gravimetry fills the gap at the shorter wavelengths not measurable by satellite techniques, especially in coastal regions where ocean circulation dynamics
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From page 47... ...
Noise in the digital elevation data of mountainous areas, which are often derived by digitizing contour lines from topographic maps, is magnified by the differencing operations used to calculate gradients. High-accuracy airborne topography measurements, with a horizontal resolution of 30 m or better and a vertical accuracy of ~ to 3 m or better, are needed to improve the solar radiation calculations described above.
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From page 48... ...
Other techniques, such as digital elevation maps, can be used to define barriers and corridors affecting species dispersal and to predict biomass, timber site quality, and burn patterns over large areas. The need for accurate slope and aspect data is especially great in semiarid, midIatitude regions where minor slope changes greatly affect local water availability, soil moisture, and vegetation cover over large areas.
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