Extending the gather record length and traces
This module is helpful in extending the gather both horizontally(traces) and vertically(time). Extending the gather is useful when doing filtering, interpolation etc.
Horizontal extension allows the data to avoid edge effects when performing filtering, FK and radon transformation. Whereas vertical extension of the gather allows not to create any artifacts top and bottom of the gather.
Why Do We Extend a Seismic Gather Horizontally?
Horizontal extension = adding traces on the left and right side of the gather.
To Avoid Edge Effects During Filtering
Many processing steps (FK filtering, Radon transform, deblending, interpolation) require operations in the frequency–wavenumber (f–k) or tau–p domain.
These transforms assume the data is continuous, but real gathers suddenly end at the boundaries → causing wraparound artifacts, edge noise, or Fourier ringing.
Extending the gather makes the edges “smoother,” reducing artifacts.
For Better Interpolation
If you want to fill missing traces or regularize spacing, algorithms behave better when they see more samples beyond the boundary.
For Accurate Tapering
We often apply cosine tapers at the edges.We cannot taper properly if there are no additional samples to taper into.
Horizontal extension provides a buffer zone.
Why Do We Extend a Seismic Gather Vertically?
Vertical extension = extending the gather in time/depth direction.
To Avoid Edge Effects in Time-Domain Filtering
Operations like:
•Band-pass filtering
•Wavelet shaping
•Deconvolution
•Tau-p transform
all assume longer time windows. Without extension, filters cause distortion at the top and bottom of the gather.
Allows Zero-Padding (Smooth FFT)
FFT-based algorithms need trace lengths that match power-of-two sizes (e.g., 1024, 2048, etc.).Vertical extension (padding) makes FFT faster and cleaner.
Improve Migration / Imaging
Imaging algorithms need more room beyond the recorded window to avoid artificial truncation of wavefields.
Why Do We Use “Mirroring” When Extending the Data?
Mirroring means copying the edges of a gather as reversed versions of itself.
Why not use zeros?
If you simply add zeros:
•The sudden jump from real amplitude → zero amplitude creates sharp discontinuities
•Fourier transform sees these as high-frequency edges
•Produces ringing and artifacts
Mirroring solves this.
Smooth Continuity at Boundaries
Mirroring ensures the ends look continuous, so filtering and FK transforms do not detect sharp breaks.
Prevents Aliasing and Wraparound
Mirrored edges behave more naturally when:
•Applying FK filters
•Running tau-p transforms
•Running Radon transforms
•Performing deblending
This reduces wraparound noise dramatically.
Preserves Local Wavefield Shape
Unlike zero-padding, mirroring preserves:
•Amplitude pattern
•Event curvature
•Frequency content
This is very important for inversion, migration, or interpolation.
Better for Slope-Based Processes
Algorithms that estimate slopes or moveout (e.g., curvature estimation) behave better when edges do not end abruptly.
Input DataItem
Input gather - connect/reference to the output gather which needs to be extended.
Mode { Extend, Revert } - choose the option from the drop down menu to perform the task. By default, Extend.
Extend - this option extends the gather as per the user specified parameters
Revert - this option reverses the previously extended parameters (time and/or traces).
Gather domain { TIME, DEPTH, FREQUENCY } - sets the input gather domain. By default, Time. Depending on the input gather, it automatically selects the gather domain. The user has no control over it.
Gather domain - TIME
Time extend - In case the input gather domain is time, specify the total time to be extended. By default, 1 ms. The extended time has zero amplitude values.
Gather domain - DEPTH
Depth extend - specify the depth to be extended. By default, 1 meter.
Gather domain - FREQUENCY
Frequency extend - specify the frequency domain extension.
Traces extend - this is for horizontal extension with respect to traces. Specify the number of traces to be extended. It will add traces on both sides of the gather and these extended traces have zero values.
Apply taper - this is important for smooth transitioning of the extended data. By default, TRUE (Checked).
Horizontal mirroring - this option allows the traces to be mirrored both sides of the existing gather. By default, TRUE(Checked).
Vertical mirroring - this option mirrors the vertical events/time at the top and bottom of the current gather. By default, TRUE(Checked).
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 extended gather as an output as well as vista item.
There is no information available for this module so the user can ignore it.
In this example workflow, we are extending a simple gather both horizontally and vertically. This gather extension can be performed inside the Seismic loop or outside of Seismic loop. It requires an input gather.
Let's add both horizontal and vertical extensions to the existing input gather and see how it looks like.
When we select "Revert" mode then everything reset to original input gather.
Apply the same parameters applied to gather extend is applicable to the gather revert also.
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
* * * If you have any questions, please send an e-mail to: support@geomage.com * * *
