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Cross-Correlation - Overview

Use the graphical and statistical cross-correlation analysis to better estimate bulk shift, phase, amplitude, and polarity corrections needed to tie your seismic lines.

Opening the Cross-Correlation Function

Right-click on the seismic you wish to adjust and select Tie with Diagnostics from the shortcut menu (or press <t> on your keyboard). Note that the seismic line must be part of a fence display in order to use the diagnostic line tie functions. Click on the Correlation tab. View image:

Understanding the Cross-Correlation Plot

The blue curve represents the normalised cross-correlation function of the active seismic line with the reference seismic line in the time domain. The red curve is the envelope amplitude of the cross-correlation function. You will know that two seismic lines are perfectly tied when:

The cross-correlation plot is symmetrical about zero time.
The largest peak in the envelope is positive and centered about zero time.

Quality Measurement

Quality is a measure of the similarity between the active and reference seismic lines. The value is posted on the cross-correlation plot. A match between two identical traces results in a maximum value of ‘1’. This maximum value can be used as a measurement of quality. Values less than ‘0.5’ indicate significant problems in matching the data. Check your diagnostics parameters to see if the cross-correlation function has valid parameters to work with.

Setting the Parameters for the Cross-Correlation Analysis

Define your area of interest by specifying a start and end time under Time Window or move the grey bar on your seismic to bracket your time range.
Select which Reference Line you which to use.
Enter the number of traces to use in the cross-correlation calculation under Average Traces.
Apply a bulk shift to center the largest peak of the envelope about zero time. The seismic is updated dynamically. Apply a phase correction to make the cross-correlation curve symmetrical about zero time. If the largest peak of the cross-correlation curve is negative, reverse the polarity. Apply amplitude corrections to match the amplitude with the reference seismic.
You can also click on the Bulk Diff, Phase Diff, or Amp Ratio correction buttons. These are an estimate based on the cross-correlation calculation of the bulk shift difference, phase difference, and amplitude ratio, respectively, between the seismic lines. The function is automatically recalculated and new suggested values are displayed.

You must roughly tie your data over a reasonable time window before these values become meaningful.

For more information about the options on this tab, see the Tie with Diagnostics dialog box.

Display Options

Change axis ranges or enable cursor tracking by clicking on Correlation Window Display Option. Click on Parameter Settings to keep parameters (such as reference line or average traces) constant in each diagnostic window or to vary the parameters from one diagnostic window to another. The Move Correlation to Separate Window allows you to view the power spectrum, coherence, or wavelet matching/transfer function windows at the same time as the cross-correlation window.

Corrections to amplitude, bulk shift, and polarity are stored in a header file and applied to traces and picks for display, picking, plotting, and export. The seismic line must be part of a fence display to enable diagnostics. See fence considerations for seismic ties.

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