Create deblending operator for Vibroseis data
A vibroseis plate sweep is the actual sweep generated by the vibrator plate and measured through sensors on the truck (ground force, reaction mass, or reference). It represents what the vibrator really produced, not just the programmed pilot sweep.
A Filtered Vibroseis Plate Sweep is the cleaned, bandwidth-limited, and harmonic-controlled version of this real sweep. It is used in:
•Deblending of simultaneous-source data
•Correlation and deconvolution
•QC of vibrator performance
•Sweep extraction from field records
Filtering ensures the sweep is:
•Smooth
•Free of unusable frequencies
•Free of most harmonic contamination
•Suitable as a reference in processing
Why Do We Filter It?
Real vibrator plates introduce:
•harmonic distortion
•mechanical noise
•limited low- and high-frequency performance
•nonlinearities
•vibrator–ground coupling variations
Filtering removes these issues so that the sweep can be accurately used for deblending and correlation.
How the module works: The module reads a SEG-Y file containing at least two channels from a vibrator truck: the first trace (channel 1) is the pilot or ideal sweep, and the second trace (channel 2) is the actual plate signal as measured by the truck sensors. Using a short-time Fourier transform (spectrogram) with a sliding Hamming-tapered analysis window, the module tracks the instantaneous frequency of the sweep at each time sample and decomposes the plate signal into N separate harmonic bands, where N is the number of harmonics specified by the user. Each harmonic band is reconstructed by inverse Fourier transform with overlap-add weighting. The resulting output gather contains one trace per harmonic component, plus the original raw plate signal, the fundamental-only contribution, and the reference pilot sweep. These harmonic component traces serve as deblending operators for subsequent simultaneous-source separation.
Input file should be provided in the Parameters tab.
Seismic filename - provide the input seismic file with sweep
Specify the path to the SEG-Y file (.sgy or .segy) that contains the vibrator sweep recordings. The file must contain at least two traces: trace 1 must be the pilot (ideal, theoretical) sweep signal as programmed for the vibrator, and trace 2 must be the measured plate signal (e.g., ground force or reaction mass signal). These two channels are the foundation of the harmonic decomposition. The file is read in full before processing begins. Ensure the two traces share the same sample interval and record length.
Number of Harmonic for de - blending - specify the total number of harmonics (additional sinusoid) for deblending. It controls how many harmonic distortion components are identified or removed. Essential for accurate deblending and characterizing Vibrator non-linearity.
Controls how many separate harmonic bands are extracted from the plate sweep signal. The default value is 1, which extracts only the fundamental sweep (the first harmonic). Setting this to 2 extracts both the fundamental and the second harmonic; setting it to 3 adds the third harmonic, and so on. Each extracted harmonic occupies one output trace in the modeled sweep gather. Vibrator nonlinearity generates harmonics at integer multiples of the instantaneous sweep frequency — for example, during a 10 Hz sweep moment, the second harmonic falls at 20 Hz and the third at 30 Hz. Higher values capture more of the harmonic distortion energy and produce more accurate deblending operators, but also require the sweep signal to contain sufficient bandwidth to hold those harmonics. For most field surveys a value of 2 or 3 is appropriate; values beyond 5 rarely add further benefit and may introduce noise.
Time window for spectrogram - spectrogram shows how frequency evolves over time. Specify the time window for spectrogram analysis. Larger windows helpful in better frequency resolution and smaller windows will helpful in time resolution.
Sets the half-length (in seconds) of the Hamming-tapered analysis window used for the short-time Fourier transform at each time sample. The full window length applied to the data is twice this value plus one sample. The default is 0.2 s. A larger window provides finer frequency resolution, which helps to separate closely-spaced harmonics; a smaller window provides better time localisation of rapidly varying instantaneous frequencies. For a typical linear upsweep at moderate sweep rates (e.g., 6–10 octaves per sweep), a window of 0.1–0.3 s gives the best balance. Reduce this value if the instantaneous frequency changes very rapidly within the sweep (fast, short sweeps) or if the harmonics are well separated in frequency. Increase it if you need to resolve harmonics that lie close together in frequency.
Sweep extraction - this section deals with the sweep extraction. Based on the user defined parameters, it will extra the sweep from the input seismic file and used it as a model sweep.
The Sweep extraction group defines the nominal frequency band of the vibroseis sweep. These values describe the theoretical sweep range as programmed for the vibrator and are used to guide the frequency-band assignment during harmonic decomposition. At each time step the module computes the expected instantaneous frequency by linearly interpolating between Fr1 and Fr2 over the full sweep duration, and uses that instantaneous frequency to assign the spectral content of the plate signal to the correct harmonic band.
Start Frequency Fr1 - specify the start sweep frequency
The low-frequency end of the vibroseis sweep, in Hz. Default is 1 Hz. Set this to match the actual start frequency used in the field acquisition parameters (typically 2–8 Hz for land vibroseis surveys). This value defines the lower bound of the fundamental sweep band and anchors the instantaneous frequency calculation. Setting it incorrectly will shift the harmonic band boundaries and degrade the quality of the extracted operators.
End Frequency Fr2 - specify the end sweep frequency
The high-frequency end of the vibroseis sweep, in Hz. Default is 5 Hz. Set this to match the actual end frequency used in the field acquisition parameters (typically 80–120 Hz for land vibroseis surveys). Together with Fr1 it defines the theoretical sweep bandwidth over the record duration. The module uses linear interpolation between Fr1 and Fr2 to estimate the instantaneous frequency at each time sample and to place the correct spectral content into each harmonic output band.
Skip - By default, FALSE(Unchecked). This option helps to bypass the module from the workflow.
When checked, the module is bypassed and no processing is performed. The input data passes through unchanged. This is useful for temporarily disabling the operator creation step while testing or QC-ing the rest of the workflow without removing the module from the sequence. By default this option is unchecked (module is active).
Modeled sweep signal - generates modeled sweep signal as an output.
The primary output of the module. This gather contains the harmonic decomposition of the input plate sweep and serves as the set of deblending operators for downstream processing. The gather has N + 3 traces, where N is the number of harmonics specified. The first N traces are the individual harmonic component sweeps (fundamental, second harmonic, third harmonic, etc.), reconstructed from the time-frequency decomposition. The next trace is the original raw plate signal (unmodified). The following trace represents the residual difference between the fundamental component and the sum of all components. The final trace is the pilot (ideal) sweep from channel 1 of the input file. These operator traces are used directly by the downstream Deblending or Iterative Deblending modules.
This module uses a time-frequency spectrogram visualization (Time-frequency spectrum) that displays how the energy of the plate sweep evolves across both time and frequency simultaneously. This view lets you verify that the harmonic components have been correctly separated. The fundamental sweep trace should appear as a clean diagonal band rising in frequency from Fr1 to Fr2 over the sweep duration. The second harmonic (if extracted) will appear as a parallel band at twice the instantaneous frequency. Use the Selected channel interactive pick to select which output trace from the modeled sweep gather is shown in the side-by-side waveform panel for detailed inspection. Left-click on the gather display to select a trace; the spectrogram and waveform panel will update immediately.
There are no action item available for this module so the user can ignore it.
YouTube video lesson, click here to open [VIDEO IN PROCESS...]
Yilmaz. O., 1987, Seismic data processing: Society of Exploration Geophysicist
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