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The CRS Method |
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The Common Reflection Surface (CRS) method is a macro-model independent imaging method in time domain, that was developed at the University of Karlsruhe, Germany. Unlike the conventional NMO/DMO stack, which requires a stacking velocity field as a macro-model, the CRS processing automatically determines the stacking parameters from semblance measurements in the prestack data. The CRS stack corresponds to a subsurface model, where reflector elements - the common reflection surface - are defined by their subsurface location, reflector curvature and dip. This general subsurface model produces stacking time surfaces which comprise the NMO/DMO, or Kirchhoff prestack depth migration time surfaces, as special cases. As a consequence, the CRS method generally provides a superior illumination of arbitrary reflectors, in comparison to NMO/DMO processing, or Kirchhoff PreSDM (Hubral, 1999). Unlike the conventional NMO/DMO stacking surfaces, the CRS stacking surfaces extend beyond single common-midpoint (CMP) gathers. This implies a much higher fold, which leads to a better signal-to-noise ratio, and reflector continuity in the CRS stack. Moreover, dipping layers are strongly enhanced, since dip is explicitly included in the CRS subsurface model. For 2D seismic data, a CRS stacking surface is determined by three parameters: the angle of incidence of the zero-offset reflection, and two radii of the wavefield curvature at the point of observation. For each point of the stack, optimum stacking parameters are automatically determined by searching for a maximum semblance along possible stacking surfaces. This automatical local optimization of the stacking parameters allows a very accurate imaging of small local inhomogeneities. Of course, the CRS stacking parameters have to be reviewed carefully, since an automatic procedure is liable to stack multiple energy as well. Hence, the search for the CRS parameters may be constrained by using a velocity model from conventional NMO analysis as a lower velocity limit. In case of land data, final static corrections have to be derived by a conventional processing prior to the CRS processing. Hence, TEEC uses the CRS processing as a valuable supplement to the conventional processing. References and suggestions for further reading: See Publications, Technical Note 12 , Technical Note 15, Technical Note 18 and Technical Note 19 |
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