Practical considerations - book
Deconvolution with multiple gates (or windows) commonly is used to correct for absorption loss of high frequencies. This approach requires that the deconvolution operators be derived from windows that are smaller than usual. Some of those windows might be too short to meet the requirements necessary for the statistical assumption that the reflectivity be random within the window. In addition, use of short windows often results in phase distortions at the zones of overlap. However, some processing systems include methods for designing smoothly varying minimum-phase inverse filters that correct for those deleterious effects.
One beneficial effect of Q-filter use is that the resulting wavelet tends to vary less in time than does the original wavelet. That is because the higher frequencies become more and more attenuated so that the wavelets become smoother and smoother. As a result, the conditions for designing a deconvolution operator for a single window are better satisfied.
Clearly, many other factors can obscure the information that one can extract from reflection amplitudes (Toksöz and Johnston, 1981). Corrections are made for the effects of spherical divergence and raypath curvature. The gain of the recording instruments is taken into account. Ray-directivity effects and amplitude-variation-with-offset (AVO) effects can be considered. Migration corrects for reflector curvature and other geometric factors. After these corrections, the following effects remain: (1) effects caused by energy losses from absorption, scattering, transmissivity losses, and peg-leg multiples, and (2) effects caused by source strength, source coupling, geophone sensitivity, geophone coupling, and source-receiver offsets. Although the effects in group 1 are difficult to determine, usually they are relatively constant along a line and therefore do not obscure lateral variations. For high multiplicity of CMP data, the effects in group 2 can be compensated for by the use of surface-consistent amplitude corrections.
- Toksöz, M. N., and D. H. Johnston, eds., 1981, Seismic wave attenuation: SEG Geophysics Reprint Series No. 2.
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