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This module constructs harmonic sweep operator models from vibroseis field recordings, which are used subsequently in the deblending workflow to suppress harmonic distortion noise. In simultaneous vibroseis acquisition, multiple vibrators excite the ground at overlapping times, and each vibrator generates not only the fundamental sweep signal but also harmonic overtones at integer multiples of the instantaneous sweep frequency. These harmonics contaminate other shot records and degrade the quality of the correlated seismic data.
The module reads a two-trace SEG-Y file containing an ideal (reference) sweep signal on the first trace and a measured vibrator plate motion signal on the second trace. It performs a time-frequency decomposition of the plate signal using a sliding Hamming-windowed FFT, separating the energy into frequency bands corresponding to the fundamental sweep and each requested harmonic. The resulting gather of modeled harmonic sweep components is written to the output and can be inspected interactively through the time-frequency spectrum display. Use this module as the first step before applying the deblending filter to your field records.
The input is a two-trace SEG-Y file specified by the Seismic filename parameter. The first trace must contain the ideal (theoretical) vibroseis sweep signal, and the second trace must contain the measured vibrator plate motion signal recorded in the field. Both traces must cover the full sweep duration and share the same sample interval. These two signals together allow the module to separate the measured plate motion into its fundamental and harmonic sweep components.
Determines how the module identifies and separates the sweep signal from the plate motion recording. This setting controls which strategy is used to detect the frequency bands corresponding to the fundamental and harmonic components of the vibroseis sweep.
Sets the number of harmonic overtones of the vibroseis sweep to model and separate. The default value is 1, which models only the fundamental sweep component. Increasing this value instructs the module to also model the second, third, and higher harmonics, producing one output trace per harmonic in the output gather. Use higher values when your data exhibits strong high-order harmonic distortion, which typically appears as linear noise at 2x, 3x, or higher multiples of the sweep frequency band on unprocessed records. Setting this too high relative to the actual harmonic content in the data will introduce modelling artefacts. A value between 1 and 4 is appropriate for most acquisition scenarios.
Controls the half-length of the sliding time window (in seconds) used for the short-time Fourier transform that computes the time-frequency decomposition of the plate motion signal. The default value is 0.2 s. A Hamming taper is applied to each window to reduce spectral leakage. Shorter windows provide better time resolution but poorer frequency resolution, while longer windows improve frequency separation of closely spaced harmonics at the cost of time smearing. For a typical 8–20 Hz sweep, values between 0.1 s and 0.5 s are reasonable. This same window length is also used when computing the interactive time-frequency spectrum display.
This group of parameters defines the frequency characteristics of the vibroseis sweep signal used during harmonic band separation.
The starting frequency of the vibroseis sweep in Hz. The default value is 1 Hz. Set this to match the actual low-cut frequency of the sweep used during acquisition. Together with the end frequency, this defines the instantaneous frequency trajectory of the sweep, which the module uses to compute the expected frequency band boundaries for the fundamental and each harmonic at every time sample. Incorrect values will cause the harmonic bands to be misidentified, leading to poor separation.
The ending frequency of the vibroseis sweep in Hz. The default value is 5 Hz. Set this to match the high-cut frequency of the sweep used in the field. The module assumes a linear sweep between Fr1 and Fr2 over the duration of the input signal, and uses the instantaneous sweep frequency at each time sample to separate the spectral energy into harmonic bands. Ensure that Fr2 is greater than Fr1 and that both values correspond to the actual survey sweep parameters.
Specifies the type of amplitude taper applied to the ends of the sweep signal to reduce edge effects during frequency-domain processing. Common options include cosine and linear tapers. A well-chosen taper suppresses spectral leakage at the beginning and end of the sweep, improving the quality of the harmonic operator models.
The sample interval of the sweep signal in seconds. This value must match the sample interval of the input SEG-Y file. It is used internally when constructing the modeled sweep waveform for frequency-band decomposition.
The time (in seconds) at which the sweep signal begins within the input trace. Set this to the onset of the active sweep portion of the plate motion recording. Energy before this time is treated as pre-sweep noise and is excluded from the decomposition.
The time (in seconds) at which the leading amplitude taper ends and the sweep reaches full amplitude. This marks the transition from the taper-on ramp to the flat-amplitude portion of the sweep. Values between T1 and T3 define the shape of the leading taper region.
The time (in seconds) at which the trailing amplitude taper begins. After this point the sweep amplitude ramps down toward zero. Together with T2 and T4, this defines the trapezoid-shaped envelope of the sweep signal used during operator construction.
The time (in seconds) at which the sweep signal ends within the input trace. Energy after this time is excluded from the harmonic decomposition. T4 should correspond to the end of the active excitation recorded on the plate motion signal.
The full path to the input SEG-Y file (.sgy or .segy) containing the vibroseis pilot sweep and plate motion traces. The file must contain exactly two traces: the first trace is the ideal theoretical sweep (reference signal), and the second trace is the measured plate motion recording from the vibrator. Both traces must have the same length and sample interval as the field sweep used during acquisition. Providing a file with incorrect trace ordering or mismatched sweep parameters will produce incorrect operator models.