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3-D GPR Home>Research Projects
Current 3-D GPR Projects
Miami Oolitic Limestone 3D GPR: Sedimentology, archeology, depositional environment |
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| Investigators: Grasmueck, Weger | ||||||||||||||||||||||||||
| This 100 MHz 3D GPR survey in an oolitic limestone environment offers new insight into the spatial distribution of sedimentary features. It was possible to image the internal architecture of a complex oolitic sandbar system on a submeter scale and to confirm relationships that exist between decimeter-scale sandwaves and the prograding barrier bar. Only the dense (0.1 x 0.2 m) grid spacing used for this survey provided the necessary basis for accurate description of 3D internal anatomy and paleoenvironmental parameters such as dominant wave and current direction. Such reconstruction of depositional environment would not have been possible with commonly used 0.5-1 m line separation. 3D GPR data volumes, together with the 3D technologies from seismic exploration, will enable unprecedented quantification of internal anatomy of sedimentary bodies, filling the scale gap between borehole and seismic information. Advances in 3D GPR data acquisition technology are needed to make such surveys commercially viable and not only a matter of academic research. Description of Movie: Horizontal-slice animation from 0 to 6 m depth through 3D-migration-processed Miami oolite 3D GPR data volume. Graphic pixels correspond to real measurements on a 0.1 x 0.2 m grid with no interpolation applied. Vertical separation of consecutive slices is 1.2 cm. By scrolling through data volume, characteristic internal patterns of anthropological and sedimentological origin can be seen: 0-1 m depth, soil with remnants of human activities; 1-2.7 m depth, dipping beds from prograding oolitic barrier bar; 2.7-6 m depth, subhorizontal ooid shoal packages with internal lineation patterns. |
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Callosa 3D GPR: Fracture imaging in Limestone |
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| Investigators: M. Grasmueck, R. Weger, H. Horstmeyer | |||||||||||||||||||||||||||||||||||
| Noninvasive 3D ground-penetrating radar (GPR) imaging with submeter resolution in all directions delineates the internal architecture and processes of the shallow subsurface. Full-resolution imaging requires unaliased recording of reflections and diffractions coupled with 3D migration processing. The GPR practitioner can easily determine necessary acquisition trace spacing on a f-k plot of a representative 2D GPR test profile. Quarter wavelength spatial sampling is a minimum requirement for full-resolution GPR recording. An intensely fractured limestone quarry serves as a test site for a 100 MHz 3D GPR survey with 0.1 m x 0.2 m trace spacing. This example clearly defines the geometry of fractures in four different orientations including vertical dips to a depth of 20 m. Decimation to commonly used half wavelength spatial sampling or only 2D migration processing make most fractures invisible. The extra data acquisition effort results in image volumes with submeter resolution both in the vertical and horizontal directions. Such 3D datasets accurately image fractured rock, sedimentary structures and archeological remains in previously unseen detail. This makes full-resolution 3D GPR imaging a valuable tool for integrated studies of the shallow subsurface. Movie Descriptions: Unmigrated 3D Timeslices: Horizontal-slice animation from unmigrated Callosa fractured limestone 3D GPR data set. Circles on slices are caused by diffractions from fractures. 3D Migrated Timeslices Horizontal-slice animation from migrated Callosa fractured limestone 3D GPR data set.With rapid animation of consecutive time slices, spatial continuity and dip of fractures can be visually assessed. Focused diffractions line up as elements of four discrete sets of fracture orientations. 3D Migrated Inlines Vertical profile animation from migrated Callosa fractured limestone 3D GPR data set. With rapid animation of consecutive profiles, spatial continuity and dip of fractures can be visually assessed. Subhorizontal fractures are traceable as semicontinuous reflections with consistent dip. Near-vertical fractures are imaged by numerous focused diffraction points aligned in steep orientations. |
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What is under the RSMAS Beach Volley Ball Court |
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| Investigators: M. Grasmueck, D. Viggiano | |||||||||||||||||
| Considering recent advances in seismic and medical 3D imaging, shallow subsurface imaging is seriously lagging behind, primarily due to lack of efficient measurement techniques supported by lightweight 3D GPR surveying equipment. Presently, it may take days to weeks to produce interpretable high resolution 3D cubes. We are currently developing a next generation acquisition system that surpasses existing equipment in productivity and precision. For a demonstration to 30 professional geologists, we recorded a 140 squaremeter 3D survey with a grid resolution of 5cm x 10cm in 50 minutes. An hour after the last trace was recorded we presented 3D animations of the internal structure of the ancient beach. Description of Movie: Before acquiring the 3D GPR survey we dug some shallow trenches in the shape of the Letters C S L and ran along it with a running water hose before closing the trenches again. Due to its sensitivity to changes in water content, the GPR images the infiltrating water. One week later slight traces of the letters were still visible on a repeat survey. Below a depth of 80 cm we can see SE dipping beds which are the sand layers of the ancient beach dipping towards the Ocean. Today the RSMAS beach is located 50m further to the SE. Circular diffractions are abundant in the middle of the survey area just underneath the volleyball net. Some players might have lost some valuable objects when smashing hard. Excavation still has to reveal the truth. |
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3D GPR imaging of a fractured and hydrothermally altered limestone quarry |
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| Investigators: M. Grasmueck, D. Viggiano, T. Smith | |||||||||||||||||
| For the first out-of-Florida test in upstate New York we packed the equipment in 8 airline checkable luggage pieces and successfully recorded during 4 days several 2D and 3D surveys. Even with low penetration depth, full-resolution 3D GPR can still provide a 'floor plan' of the fracture network in an outcrop covered with rubble. Based on the GPR survey results, the most interesting excavation sites can be chosen. Description of Movie: Horizontal slices through 3D GPR survey covering an area of 26.3 m x 30 m with a survey grid of 0.05 m x 0.10 m using 250 MHz GPR antennae. Depth range 0.67 m to 0.93 m. Interpretation on 0.8 m depth slice: Yellow = outline of buried fault segment, Red= fractures, Green = topography related to buckling up of elsewhere horizontal strata on the East side of the fault and slight depression to the West. |
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Using 4D GPR to Track Fluid Flow in the Vadose Zone |
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