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The Frequency Spectrum f-t module computes a time-varying amplitude-frequency spectrum for a seismic gather. Unlike a single static spectrum, this module produces a two-dimensional frequency-vs-time (f-t) matrix that shows how the frequency content of the data evolves with time. This is a quality control and analysis tool — it does not modify seismic traces.
For each time sample in the input gather, the module applies a triangular taper window of the specified length around that sample and computes a Fast Fourier Transform (FFT) for every trace. The resulting amplitude spectra are averaged across all traces to produce a single spectrum at that time position. This process is repeated for all time samples, building the full f-t matrix. The matrix is normalized to decibels (dB) relative to the maximum amplitude, and then optionally smoothed along the time axis. Two output views are produced: the full 2D frequency-time matrix and a 1D average spectrum curve showing mean amplitude versus frequency across the entire record.
Use this module to identify frequency variations with depth, to detect band-limited noise, to verify the effect of frequency filters, or to assess the usable frequency bandwidth at different time levels in the data.
The seismic gather to be analyzed. This can be a pre-stack common-midpoint gather, a shot gather, or any other gather type. All traces in the gather contribute to the spectrum — they are processed individually and their amplitude spectra are averaged together at each time position. A gather with more traces produces a more statistically stable spectrum.
The half-length of the analysis window used to compute the spectrum at each time position, expressed in samples. The actual window applied spans 2 × Sample window + 1 samples, centered on the current time sample, and is tapered with a triangular (Bartlett) weight that reduces edge effects. The FFT is computed on this windowed segment.
Larger values improve frequency resolution but reduce time resolution — fine frequency detail will be visible, but the spectrum will respond more slowly to changes in signal character with depth. Smaller values sharpen time localization at the cost of coarser frequency resolution. The default value is 40 samples. The minimum allowed value is 10 samples.
The half-length of a box-smoothing filter applied along the time axis of the computed f-t matrix, expressed in seconds. After the frequency-time matrix is built, a running average is applied to each frequency slice over a window of 2 × Smooth window + 1 samples (converted from seconds using the trace sample interval). This reduces trace-to-trace noise in the spectral estimate, producing a smoother and more interpretable display.
Increase this value when the f-t matrix appears noisy and you want a cleaner overall picture of spectral trends. Decrease it when you need to preserve sharp time-localized spectral features. The default value is 0.160 s (160 ms). The value must be greater than zero.
A 2D matrix display with frequency (Hz) on the vertical axis and time (s) on the horizontal axis. Each cell shows the average amplitude of that frequency component at that time position, expressed in dB relative to the global maximum. This view allows you to see how the frequency content of the seismic data changes with time — for example, gradual high-frequency attenuation with depth, or the presence of noise at specific frequencies.
A 1D curve showing the average amplitude spectrum of the gather, with frequency (Hz) on the horizontal axis and amplitude (dB) on the vertical axis. This is computed by averaging the f-t matrix over all time samples at each frequency, yielding a single representative spectrum for the entire gather. Use this view for a quick overview of the dominant frequency band and to compare the spectral shape before and after processing steps.