HR: 0800h
AN: U21B-0820    [Abstracts]
TI: Multicomponent Ground Penetrating Radar to Image Sedimentary Structures Exhibiting Directionality
AU: * Sassen, D S
EM: dsassen@geo.tamu.edu
AF: Texas A&M University, The Department of Geology and Geophysics Texas A&M University, College Station, TX 77843-3115 United States
AB: Ground penetrating radar (GPR) is often used in the study of sedimentary deposits because its resolution provides detail similar to outcrop studies. These studies often utilize only a single antenna configuration in a single orientation and use scalar processing techniques. However, the ability to excite and receive responses with GPR from geologic features that have high degrees of directionality, including faults, fractures, dipping beds, and cross-bedding, depends strongly on the polarization of the radar antennas with respect to the orientation or strike of subsurface features. Also, the received response of the subsurface strongly depends on the antenna configuration used. While these dependencies are often seen as problems, these issues can be used to advantage in the study of sedimentary deposits. By using a multicomponent GPR survey technique that utilizes to the vector nature of electromagnetic waves, received instantaneous amplitude signals can be represented by a second-rank tensor. Using Alford rotations it is possible to determine the strike of directional sedimentary features, and field studies show that is can be used to produce apparent images of the subsurface for any antenna orientation for co-polar and cross-polar antenna configurations. Cross-polarized configurations are sensitive to only depolarizing features such as dipping beds and rough surfaces, while co-polarized configurations are sensitive to both normal reflectors and depolarizing features. In field data, Alford rotations on multicomponent GPR data from point-bar deposits from the Brazos River in Texas were used to determine feature orientations and to produce migrated apparent images that provide insight into the overall architecture of the point-bar. From the multicomponent data sedimentary features are classified on the basis of orientation and the ability to depolarize the signal. This gives additional information that is used in the interpretation of the radar stratigraphy. This information is utilized to assess the flow direction, location relative to the channel, and the location within the point-bar. In some cases multicomponent GPR techniques can be used to identify and remove signals from faults and fractures that obscure sedimentary features.
DE: 0600 ELECTROMAGNETICS
DE: 0604 Antenna arrays
DE: 0694 Instruments and techniques
DE: 0900 EXPLORATION GEOPHYSICS
SC: Union [U]
MN: Fall Meeting 2005