Vibroseis Test1441 ProMAX® Reference

Vibroseis Test

Vibroseis Test performs an analysis on two signals:Reference and Vibrator, in order to analyze the quality ofvibrators.

Theory

The quality of data acquired using Vibroseis as a source canbe improved by frequently monitoring the quality of vibrators.In-time identification and fixing vibrator problems such as,phase or harmonic distortion, in the field is very importantsince the processing cannot compensate for the fieldhardware problems. Vibrator signal can be recorded on abaseplate or reaction mass as well.

Harmonic and relative characteristics computation algorithmis based on analysis in windows. Each window is 500 mslong. Windows are 50% overlapped. Analyzing window istapered with cosine taper on the edges and Fouriertransformed to a frequency domain. After that amplitudespectrum of the window is computed (A). Maximum value inamplitude spectrum is considered to be a fundamentalfrequency (FF). Total fundamental energy (TFE), total oddenergy (TOD) and total even energy (TEE) are then calculatedas follows:

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Vibroseis Test1442 ProMAX® Reference

TFE =

TEE =

TOE =

%THD =

References

Gardner, R., 1989, Vibroseis, Geophysics Reprints Series No. 11.

Rietsch, E., 1977. Computerized Analysis of Vibroseis Signal Similarity, Geophys-ical Prospecting 25, 541-552.

Martin, J.E. and White, R.E., 1989, Two methods for continuous monitoring of har-monic distortion in Vibroseis signals, Geophysical Prospecting 37, 851-872.

Digital Seismic Recorder Specification Standards, 1988, SEG.

Usage

After you have successfully entered parameters and executedthe program three graphic plots will be available for analysisand geophysical interpretation: Sweeps, Correlation andHarmonics. The following color convention is used: bluecorresponds to a Reference sweep and its characteristics,brown corresponds to a Vibrator sweep and itscharacteristics, and pink corresponds to a mutual Reference-Vibrator characteristics, such as cross correlation or phasedifference.

• Sweeps Plot holds Reference sweep, Vibrator sweep,there amplitude spectra, Reference and Vibrator sweepsoverlapped and Phase difference between Reference andVibrator. A positive phase difference represents a posi-tive phase shift of Vibrator relative to the Reference. Thephase spectrum will be zero for frequencies which have

A2

f(f 0.5FF=

1.5FF

∑

A2

f( ) A2

f( ) …+f 3.5FF=

4.5FF

∑+f 1.5FF=

2.5FF

∑

A2

f( ) A2

f( ) …+f 4.5FF=

5.5FF

∑+f 2.5FF=

3.5FF

∑

100.TOE TEE+( )

12---

TF E

12---

-------------------------------------

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Vibroseis Test1443 ProMAX® Reference

cross power less than -80db relative to the maximumcross power of Vibrator and Reference.

• Correlation Plot holds autocorrelations of Referenceand Vibrator, there cross correlation, logarithmic enve-lopes of auto- and cross- correlations, and frequencydomain representation of correlations.

• Harmonics Plot holds graphic of Total Harmonic Distor-tion in percent, Frequency-Time representation of Refer-ence and Vibrator sweeps, which helps to see vibratorharmonics.

You can use the following icons while in a graphics session:Stop, Continue, and Print. Zoom capability is enabledautomatically for each of the plots.

Parameters

Record selection choice

Select the record choice. The options are:

• FFID

• Source Index No.

Record number to input

Enter the record number of the reference and vibratorsweeps.

Reference sweep channel number

Enter the channel number of the Reference sweep.

Vibrator sweep channel number

Enter the channel number of the Vibrator sweep.

Start time of record (ms)

Enter the start time of the input record. Enter 0.0 to startwith the first sample.

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Vibroseis Test1444 ProMAX® Reference

End time of record (ms)

Enter end time of the input record. Enter 0.0 to finish inputwith the last sample.

Enter label for test

Enter the input string label for this test.

Hardcopy POSTSCRIPT device name

Enter the name of a a PostScript printer to dump currentgraphics. The syntax is similar to the command line.

Interactive Display

• Sweeps Button allows you to go to the Sweeps graphicplot.

• Correlation Button allows you to switch to the Correla-tion graphic plot.

• Harmonics Button allows you to switch to the Harmon-ics graphic plot.

• Stop Icon allows you to stop and abort the current flow.

• Continue Icon allow you to proceed with the currentflow.

• Print Icon allows you to dump a current screen to aPostscript device.

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