Changes

Surface-consistent amplitude corrections are also necessary when amplitude variations in the data may relate to source and receiver environment and not to the geology. These corrections are distributed among the surface terms of source, receiver, and offset, plus a single subsurface (CDP or geological) term.

Surface-consistent amplitude corrections are also necessary when amplitude variations in the data may relate to source and receiver environment and not to the geology. These corrections are distributed among the surface terms of source, receiver, and offset, plus a single subsurface (CDP or geological) term.

Normal moveout (NMO) and residual statics corrections must be performed as accurately as possible, for any AVO analysis is degraded by inappropriate corrections. The recent use of interactive processing workstations is providing explorationists with the necessary control over the selection of correct stacking velocities (see "[[Integrated computer methods]]").

[[Basic seismic processing#Normal moveout (NMO) correction|Normal moveout]] (NMO) and [[residual statics correction]]s must be performed as accurately as possible, for any AVO analysis is degraded by inappropriate corrections. The recent use of interactive processing workstations is providing explorationists with the necessary control over the selection of correct stacking velocities.

Signal to noise ratio improvements must occur on individual traces in the CDP gathers. Robust deconvolution is important to preserve stability of the wavelet across all offsets. In the land data case, a surface-consistent deconvolution method is usually desirable. To further stabilize the wavelet, deconvolve the data to a desired target waveform with frequency cutoffs predetermined by knowledge of the input data's usable frequency range. Trace-dependent deconvolution, such as a spiking operator, can sometimes produce severe distortions in reflector waveform when the signal to noise ratio is low on some of the individual traces.

Signal to noise ratio improvements must occur on individual traces in the [[CDP gather]]s. Robust deconvolution is important to preserve stability of the wavelet across all offsets. In the land data case, a surface-consistent deconvolution method is usually desirable. To further stabilize the wavelet, deconvolve the data to a desired target waveform with [[frequency cutoff]]s predetermined by knowledge of the input data's usable frequency range. Trace-dependent deconvolution, such as a [[spiking]] operator, can sometimes produce severe distortions in reflector waveform when the signal to noise ratio is low on some of the individual traces.

Multiple interference can render amplitude with offset analysis of the CDP gathers meaningless. Generally, multiples are more dominant in data from the marine environment, but can also be strong in land data. Multiples are usually not visually evident in land data because of trace spacing and lower fold and will appear as strong random noise. But proper use of multiple removing programs, such as radon transform methods, can yield excellent results.

[[Basic seismic processing#Demultiple|Multiple interference]] can render amplitude with offset analysis of the CDP gathers meaningless. Generally, multiples are more dominant in data from the marine environment, but can also be strong in land data. Multiples are usually not visually evident in land data because of trace spacing and lower fold and will appear as strong random noise. But proper use of multiple removing programs, such as [[radon transform method]]s, can yield excellent results.

[[:file:amplitude-versus-offset-avo-analysis_fig4.png|Figure 4]] shows NMO-corrected CDP gathers that have been processed with the proper amplitude corrections and cascaded noise reduction methods. It is critical that noise be removed without smearing the signal or introducing artifacts, which often occurs with multichannel filtering techniques.

[[:file:amplitude-versus-offset-avo-analysis_fig4.png|Figure 4]] shows NMO-corrected CDP gathers that have been processed with the proper amplitude corrections and cascaded noise reduction methods. It is critical that noise be removed without smearing the signal or introducing artifacts, which often occurs with multichannel filtering techniques.