Development of a field method for subsurface remote imaging through implementation of seismic geophysical diffraction tomography.

摘要

Geophysical diffraction tomography is a remote sensing technique with theoretically proven capabilities for high resolution subsurface imaging. The primary steps of the technique are (1) an acoustic wave is projected through a subsurface cross-section to a hydrophone array located vertically in a borehole, (2) the amplitude versus time signal of the propagating wave is collected at each hydrophone, and (3) the reduced wave equation and theory of backpropagation tomography are invoked to reconstruct the subsurface features from the collected data. This dissertation describes the first efforts to resolve the formalism of the theory into a imaging procedure that is executable with actual field data. The steps accomplished in achieving this objective were (1) the theory of diffraction tomography was reviewed to define the steps required to develop a field implementable procedure, (2) data collection procedures were developed to compile the raw data dictated by the imaging procedure, (3) an automated data management and analyses program was constructed to resolve the collected data into the input data set for the imaging program, (4) a buried object detection procedure was developed and evaluated to enhance the field practicality of diffraction tomography, and (5) actual subsurface images showing an isolated buried object were produced from data collected in two field studies. Described are the numerous advantages implementation of diffraction tomography offers in comparison with existing remote sensing methods being applied in hazardous waste site characterization work. Further, additional uses in the environmental engineering were shown to be feasible based on the theory of the technology and the findings of the initial field implementation efforts.