Seismic time sections ideally represent a vertical cross-section of the earth. By using reflection amplitude and character on these time sections, lateral events are picked from trace-to-trace and these events are then interpreted as geologic boundaries between formations which have different acoustic impedances.
In order to increase the signal-to-noise ratio on the time sections and, at the same time, provide a velocity distribution profile of the earth, multi-fold data acquisition techniques are employed. In these field techniques, all reflecting interfaces below a common surface point are specularly illuminated, at least six times, by varying the offset distance between the source and receiver. Multifold data are acquired for those source-receiver pairs which are centered around a common surface point.
Processing techniques, some standard to image processing, such as deconvolution, stacking and gain correction, are then implemented. However, because the source and receiver are omni-directional, energy reflecting or diffracting from points not vertically beneath the common surface point can obscure the geophysicist’s interpretation. These non-vertical features, as fortune will have it, are normally the zones of economic value. The processing algorithms, which place this non-vertically traveling energy in its true spatial position, are called Migration Techniques. They are imaging processes, which are anologues to a Kirchhoff or backward wave propagation reconstruction, that is a form of synthetic aperture imaging.
Because of the massive amounts of data involved, very efficient algorithms have been developed for migration. Only minute differences are evident between the time-domain (finite difference or backward propagation summing) and frequency-domain methods.
Currently, seismic research in total of 3-D imaging is very active in areas of data acquisition, processing, display and interpretation.
KeywordsAcoustic Impedance Seismic Section Time Section Geophone Array Seismic Imaging
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