Browsing by Author "Egan, Mark Stephen"
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Item Digital reconstruction from Fourier projection data(1978) Egan, Mark Stephen; Cook, Bill D.; Wang, Keith Y.; Kleis, Stanley J.Presented is the theoretical basis for reconstruction of 2-dimensional signals in the Fourier plane from projection data. Three algorithms are studied in detail: the Hankel transform method, the 2-dimensional interpolation method, and the concentric squares raster method. Each algorithm is programmed and applied to simulated projection data. The results are compared. The applicability of these techniques to mapping ultrasonic fields is considered, and the use of minicomputers discussed.Item Dispersive and anisotropic aspects of stratigraphic filtering(1988) Egan, Mark Stephen; McDonald, John A.; Gardner, Gerald H. F.; Sheriff, Robert E.; Norman, Carl E.When seismic waves propagate through thinly layered sequences, anisotropy and dispersion can be induced (even when the comprising beds are isotropic and elastic). This is of interest to the exploration community since ignoring such effects can have hazardous implications. Numerical experiments using both wave- and ray-theoretical techniques were conducted with a periodic, binary sequence of beds. When tuning frequencies were outside the bandwidth of an incident, compressional wavelet, the stratified model behaved as a homogeneous, transversely isotropic medium. When the layers of the model were thick enough for the tuning frequencies to fall within the bandwidth of the pulse, dispersion generally resulted. Amplitude and phase spectra of the earth filter showed that the dispersion was not that associated with a frequencyindependent Q value. One-dimensional modeling revealed that these induced phenomena result from the superposition of internal multiples. Two-dimensional tests showed that inhomogeneous waves can play a key role in the apparent propagation of body waves in stratified environments.