Selecting and excluding higher amplitudes traces
Clip Selector is used to determine the clipping value (or gain level) for seismic data display and processing. Its primary purpose is to control the amplitude scaling of seismic traces to optimize their visual representation. Clip selector works trace by trace mode.
Why is it needed? Seismic data can have an enormous dynamic range, from very weak deep reflections to very strong shallow reflections or noise bursts. If we plot this data with a fixed scale, either the strong amplitudes will saturate ("clip") and obscure all detail, or the weak amplitudes will be invisible. The clip selector automatically or manually calculates a sensible maximum value to which all amplitudes will be scaled, ensuring a balanced and geologically informative display.
Clip selector modules works like a select traces module. Whenever there are higher amplitude traces in the gather/volume, it will select these traces and exclude from the final output based on the user defined maximum amplitude value. So the user must keep in mind that the final output data has less number of traces than the input data.
Input DataItem
Input gather - connect/reference to the Output gather that got higher amplitudes which needs to be excluded.
Maximum value - provide the maximum amplitude value that needs to be considered.
Clip selection type { By average, By absolute maximum } - it allows the user to select the type of clipping
By average - calculates the clipping values by averaging the amplitudes. This calculates the root mean square (RMS) or simple average values of the data. Later this value clipping value is set as a multiple of this average value. Since it is an average value, it is good and robust and not sensitive to single or random noise bursts.
By absolute maximum - this methods finds the single highest amplitude value in the entire dataset and sets this value as a clipping value. Unlike average, this method is very sensitive to outliers (a single trace with higher amplitude) can dominate the scaling.
Zero time - this is the time window that is used to calculate the clipping value. Instead of analyzing the whole trace, the user can design multiple overlapping time windows. This clip selector calculates a unique clip value.
Auto-connection - By default, TRUE(Checked).It will automatically connects to the next module. To avoid auto-connect, the user should uncheck this option.
Bad data values option { Fix, Notify, Continue } - This is applicable whenever there is a bad value or NaN (Not a Number) in the data. By default, Notify. While testing, it is good to opt as Notify option. Once we understand the root cause of it,
the user can either choose the option Fix or Continue. In this way, the job won't stop/fail during the production.
Notify - It will notify the issue if there are any bad values or NaN. This will halt the workflow execution.
Fix - It will fix the bad values and continue executing the workflow.
Continue - This option will continue the execution of the workflow however if there are any bad values or NaN, it won't fix it.
Number of threads - One less than total no of nodes/threads to execute a job in multi-thread mode. Limit number of threads on main machine.
Skip - By default, FALSE(Unchecked). This option helps to bypass the module from the workflow.
Output DataItem
Output gather - generates the output gather after amplitude clipping.
There is no information available for this module so the user can ignore it.
In this example workflow, we are adding some higher amplitudes to a stack gather by using Expression calculator. Later by using Clip selector, we are excluding these higher amplitudes.
If we look at the Expression calculator, it is something like this
The above output is connected/referenced to Input gather of Clip Selector. Adjust the parameters to eliminate the higher amplitudes.
If we look at the output gather of both Expression calculator & Clip selector, they will display two different trace header information.
We can clearly see that there are less number of traces after Clip selector. These are the higher amplitude traces which are excluded by Clip selector module based on the user defined amplitude values.
There are no action items available for this module.
YouTube video lesson, click here to open [VIDEO IN PROCESS...]
Yilmaz. O., 1987, Seismic data processing: Society of Exploration Geophysicist
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