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Line 51: − − [[file:basic-seismic-processing_fig3.png|left|thumb|{{figure number|3}}The shot record of Figure 1 after the application of a gain recovery algorithm to replace the energy lost as the signal traverses the earth. © Landmark/ITA.]] − − [[file:basic-seismic-processing_fig4.png|thumb|{{figure number|4}}The shot record after a statistical deconvolution process has been applied to “shorten” the wavelet and increase time resolution. Copyright Landmark/ITA.]] − − [[file:basic-seismic-processing_fig5-part1.jpg|left|thumb|{{figure number|5a}}The application of statics corrects for differences in arrival time caused by elevation or weathering. (a) The valley in the data to the left of station 1500 represents an anomaly that persists throughout the time length of the record. Copyright Landmark/ITA.]] − [[file:basic-seismic-processing_fig5-part2.jpg|left|thumb||{{figure number|5b}}The application of statics corrects for differences in arrival time caused by elevation or weathering. (b) This “static” effect has been corrected. Copyright Landmark/ITA.]] Line 76:
Line 75: − − [[file:basic-seismic-processing_fig6.jpg|thumb|{{figure number|6}}(a) A gather of processed traces with a common surface location. Shot-to-receiver offset is zero at the center of the gather and increases to about 2000 m deep on either end. The offset related curvature of the reflections is due to normal moveout. (b) Normal moveout correction (NMO) has been applied and the horizons are flat. The gather is now ready to be summed or stacked to produce one trace on Figure 2. Copyright Landmark/ITA.]]
→Typical processing steps
==Typical processing steps==
==Typical processing steps==
[[file:basic-seismic-processing_fig3.png|left|thumb|{{figure number|3}}The shot record of Figure 1 after the application of a gain recovery algorithm to replace the energy lost as the signal traverses the earth. © Landmark/ITA.]]
[[file:basic-seismic-processing_fig4.png|thumb|{{figure number|4}}The shot record after a statistical deconvolution process has been applied to “shorten” the wavelet and increase time resolution. Copyright Landmark/ITA.]]
[[file:basic-seismic-processing_fig5-part1.jpg|left|thumb|{{figure number|5a}}The application of statics corrects for differences in arrival time caused by elevation or weathering. (a) The valley in the data to the left of station 1500 represents an anomaly that persists throughout the time length of the record. Copyright Landmark/ITA.]]
[[file:basic-seismic-processing_fig5-part2.jpg|left|thumb||{{figure number|5b}}The application of statics corrects for differences in arrival time caused by elevation or weathering. (b) This “static” effect has been corrected. Copyright Landmark/ITA.]]
[[file:basic-seismic-processing_fig6.jpg|thumb|{{figure number|6}}(a) A gather of processed traces with a common surface location. Shot-to-receiver offset is zero at the center of the gather and increases to about 2000 m deep on either end. The offset related curvature of the reflections is due to normal moveout. (b) Normal moveout correction (NMO) has been applied and the horizons are flat. The gather is now ready to be summed or stacked to produce one trace on Figure 2. Copyright Landmark/ITA.]]
Given the broad categories of processing functions just described, this section briefly defines the common programs by their generic names in the order they would normally be applied. Some steps may be applied more than once at different times in the sequence, while others may be skipped for a particular dataset.
Given the broad categories of processing functions just described, this section briefly defines the common programs by their generic names in the order they would normally be applied. Some steps may be applied more than once at different times in the sequence, while others may be skipped for a particular dataset.
The association by unique identifier of each recorded trace with shot and receiver locations.
The association by unique identifier of each recorded trace with shot and receiver locations.
===Antialias filter===
===Antialias filter===
A low pass filter applied before resampling the data to a coarser time scale to prevent aliasing. Aliasing is a phenomenon in which high frequency data masquerades as low frequency energy as a result of undersampling. To sample a signal properly, there must be at least two samples within the shortest period of interest. Antialias filters remove frequencies above the sampling limit (Nyquist frequency) of the new sampling time. The operation is performed before the sampling is reduced.
A low pass filter applied before resampling the data to a coarser time scale to prevent aliasing. Aliasing is a phenomenon in which high frequency data masquerades as low frequency energy as a result of undersampling. To sample a signal properly, there must be at least two samples within the shortest period of interest. Antialias filters remove frequencies above the sampling limit (Nyquist frequency) of the new sampling time. The operation is performed before the sampling is reduced.
===Gain recovery===
===Gain recovery===
The correction for the loss in amplitude of a signal as it travels through the earth and spreads its energy over a larger surface area. This involves multiplication of the signal by a number that increases with time. The exact time variant multiplier can be based on the theoretical concept of spherical spreading (related to the square of the distance traveled), can be based on measurements of amplitude decay with time made on the data itself, or can be entirely arbitrary. An example of the effect of gain recovery is given in [[:file:basic-seismic-processing_fig3.png|Figure 3]].
The correction for the loss in amplitude of a signal as it travels through the earth and spreads its energy over a larger surface area. This involves multiplication of the signal by a number that increases with time. The exact time variant multiplier can be based on the theoretical concept of spherical spreading (related to the square of the distance traveled), can be based on measurements of amplitude decay with time made on the data itself, or can be entirely arbitrary. An example of the effect of gain recovery is given in [[:file:basic-seismic-processing_fig3.png|Figure 3]].
===Deconvolution===
===Deconvolution===
Acoustic signals that are not reflections from subsurface layers appear in shot records ([[:file:basic-seismic-processing_fig1.png|Figure 1]]) as straight lines rather than hyperbolic curves. These events have a constant “apparent velocity” as they travel along the receiver cable. This simple organization allows them to be isolated from the reflection signal and to be removed from the record. A common way to do this is with the FK (sometimes called pie slice) filter. Judicious selection of the range of apparent velocities to be removed can eliminate linear noise. Too wide a filter can remove too much information from the section and causes serious interpretation problems.
Acoustic signals that are not reflections from subsurface layers appear in shot records ([[:file:basic-seismic-processing_fig1.png|Figure 1]]) as straight lines rather than hyperbolic curves. These events have a constant “apparent velocity” as they travel along the receiver cable. This simple organization allows them to be isolated from the reflection signal and to be removed from the record. A common way to do this is with the FK (sometimes called pie slice) filter. Judicious selection of the range of apparent velocities to be removed can eliminate linear noise. Too wide a filter can remove too much information from the section and causes serious interpretation problems.
===Normal moveout (NMO) correction===
===Normal moveout (NMO) correction===