QC prestack data — g-Viewer
QC prestack data

Seismic data QC software

Quick QC of pre-stack data, geometry and spectra. Play through common shot, receiver and bin gathers, read the moveout against a velocity line, cross-plot any three trace headers to find the mistake, and compare the spectrum of one part of the record with another.

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CS · CR · CDP
A tab for each domain
3 headers
Two axes and a colour
Many regions
Spectra side by side
A g-Viewer pre-stack QC workspace: common-gather display, a colour-coded QC graph of trace headers, a header histogram, a spectrum panel and a location map
In view
Gathers, QC graph, histogram & map
Pre-stack QC is mostly a question of looking at enough of the data. g-Viewer's answer is to make looking cheap: gathers play through automatically at whatever interval you set, a velocity line sits on top of them so the moveout has something to be read against, and every trace header in the file is one right-click away from being an axis on a cross-plot. The views stay in step. Pick a row in the header table and that trace is marked on the section, on the location map and on the QC graph at the same time — so a suspicious point on a plot is immediately a place on the survey.
Gathers

Shot, receiver and bin, each in its own tab.

The common-gather view groups traces by offset, shot or receiver — the arrangement pre-stack work is done in, and the one velocity analysis and AVO studies start from.

Sort
Group by, and sort by

Four tabs run across the main window: Seismic data, Common shot, Common receiver and Common bin. Group by builds the gather from the trace headers you pick, and the gathers can be sorted on selected headers — by FFID and offset, for instance. Loading order is sequential by default, or grouped when you want it to follow the sort.

Animate
Play through the line

Set an interval in milliseconds, a velocity, an optional shift and a maximum trace count, then Start: gathers advance one after another until you stop. To Begin, Prev and Next step through by hand. Watching reflections change gather by gather is what turns a missing or inconsistent trace from a needle into something you notice.

Velocity
A line over the moveout

A near-surface velocity line can be plotted on the gathers — and a shift moves the lines down rather than moving the data, so the comparison stays honest. If the line does not appear, its vista item needs to sit above the gather in the layer order.

Select
From the map

With the control item set to selected common gather, clicking the location map opens the shot, receiver or CMP gather at that position in its own tab.

Headers

Any three headers, two axes and a colour.

The trace-header table is the control surface for the QC graph. Right-click a column, send it to the horizontal axis; do the same for the vertical; give a third header to the colour. The plot appears in the QC graph view.

Three-header cross-plot
Two headers on the axes, a third in colour. Any of them, in any combination — the manual's own examples are FFID against offset coloured by channel.
Header histograms
A histogram of a header field across the dataset, used to catch missing data, outliers and binning irregularities before the data goes on to stacking or migration.
Ranges at a glance
The Trace data panel lists every header with its format, start byte, current value, its minimum-to-maximum range over the dataset and a small histogram — variability and anomalies without plotting anything.
Synchronised selection
Click a row in the header table and the trace is drawn on the seismic as a dotted line, on the location map as a green line and on the QC graph as a circled dot.
Fix a header
The expression column edits header values by formula — a metres-to-feet conversion on a coordinate byte, say. Read Headers applies it in the panel.
Write it back
Save Trace Header updates the chosen headers in the current SEG-Y; Save Seg-Y writes a new file, all traces or selected ones, resampled if needed.
Spectral analysis
The same spectrum tool sits on the gather view's toolbar, so a shot record's bandwidth can be checked in the place you are already looking at it.
Type safety
If an expression does not match the header's data type, g-Viewer says so rather than writing something wrong into the file.
Spectra

Compare one region against another.

Spectral Analysis is built around selecting more than one area of a single dataset, so the question "is this part of the record different?" gets answered on one plot instead of two.

Spectral Analysis
Measuring the frequency content
Multiple regions
Activate the tool at the top of the view and drag out as many regions of interest as you want within one dataset; each gets its own spectrum.
Colour-matched
Each selection's colour is shared by its rectangle on the section and its curve on the plot, so the pairing needs no legend.
Four representations
Amplitude, phase, energy and a decibel scale of the same spectral content.
Controls
Spectral smoothing, a maximum-frequency limit, zoom into a frequency range with auto-fit, and export of the results.
Default
With nothing selected, g-Viewer shows the spectrum of the full visible section.
Band-pass filtering
Testing a band without committing to it
Where
Enabled in the View properties panel with the Enable band-pass option.
F1
The lower cutoff, taking out very low-frequency noise.
F2
The upper cutoff, taking out high-frequency noise.
Effect
Visual only — the manual states plainly that band-pass filtering does not modify the input seismic data.
Alongside
Gain and an AGC window are per-item display settings on the same panel, for visualization and for comparing one section against another.
What it catches

The checks these tools are actually for.

A cross-plot and a sorted gather are general tools; these are the specific problems they are good at surfacing in a pre-stack dataset.

1
Header values that do not fit
Unexpected offsets, wrong shot numbers, missing or duplicate traces — visible as points off the trend on a cross-plot.
2
Source–receiver geometry
Offset against FFID shows whether shot spacing is uniform and where an irregular shot pattern points at an acquisition error.
3
Marine and land specifics
Shot point, receiver distance and channel number together for marine positioning; azimuth, offset and elevation for terrain effects on land.
4
Instrument and processing errors
Trace gain against channel number exposes variations in scaling, gains or filter application across the spread.
5
Binning and navigation
CDP against offset coloured by shot point finds incorrect binning and overlapping or missing bins; source X against source Y coloured by FFID finds navigation inconsistencies.
6
Gathers that do not belong
Sorting and grouping isolates misaligned or corrupted traces, and confirms headers are assigned to the right gathers before anything downstream depends on it.
More g-Viewer capabilities

QC happens across the whole workspace.

Gathers, the map, the header table and the 3D scene are different windows onto the same selection. These are the other g-Viewer topics.

g-Viewer overview Seismic data view 3D view Multiple datasets Location map More formats & plug-ins
FAQ

Questions, answered.

Which gathers can I look at?
The main window carries four tabs — Seismic data, Common shot, Common receiver and Common bin — so the whole dataset and each gather domain have their own display. Group by lets you build the gather on the trace headers you choose, and gathers can be sorted on selected headers. The common-gather view groups traces by offset, shot or receiver, which is the arrangement velocity analysis, AVO work and noise assessment all start from.
How does gather animation work?
The animation controls sit in the Common gather bar. Set the interval in milliseconds between frames, a velocity, an optional time shift and the maximum number of traces to read, then press Start and gathers play through one after another until you stop or pause. To Begin, Prev and Next step through them by hand. It is the fastest way to see reflections change across a line and to catch inconsistent or missing traces.
Can I check geometry from the gathers?
Yes, two ways. A near-surface velocity line can be plotted over the gather from the Common gather bar, so the moveout of the first arrivals can be read against it — a shift pushes the velocity lines down rather than moving the data. And the QC graph cross-plots any three trace headers, two on the axes and a third in colour, which the manual recommends for exactly this: offset against FFID for shot spacing, CDP against offset coloured by shot point for binning, source X against source Y for navigation.
Can I compare spectra from different parts of the data?
Yes. Spectral Analysis lets you drag out several regions within a single dataset and plots the spectrum of each one, colour-matched to its rectangle on the section, with amplitude, phase, energy and dB representations, smoothing, a maximum-frequency limit and export. The band-pass filter itself — F1 and F2 cutoffs in View properties — is visual only and does not modify the input data.
Get started free

QC your own gathers this afternoon.

g-Viewer is a fully functional free trial with auto-update, for Windows, Linux and macOS on Apple Silicon. Load a shot record and start the animation.

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