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PSTM imaging (also referred to as VTI analysis) is an interactive anisotropy analysis module for Pre-Stack Time Migration (PSTM) data. It computes semblance panels over a range of the anisotropy parameter eta (η) for common-image gathers (CIGs) that already have NMO applied, and enables interactive picking of the optimal η function. The picked η model is then applied to flatten residual moveout and can be exported as eta-corrected gathers and stacks for both the inline and crossline directions.
This module is used in anisotropic PSTM workflows where vertical transverse isotropy (VTI) parameters need to be estimated from the data. After picking, use the Create eta applied gathers and Create output stacks custom actions to produce the final imaging outputs. Corridor eta picking constrains the auto-picker to a user-defined eta corridor to improve picking stability on complex data.
Flag indicating whether the input CIGs already have NMO correction applied. Set to true (default) when the gathers are post-NMO; set to false when the module should internally apply NMO before computing the eta semblance.
SEG-Y file handle used to read the PSTM CIG data from disk for interactive display and processing.
Trace header vector providing inline, crossline, and offset information required to organise CIGs for semblance analysis.
Root-mean-square velocity model used to compute the NMO moveout curve and to parameterise the eta semblance calculation. Connect the VRMS field used during the PSTM migration.
Persistent storage item for the interactively picked eta function. This item accumulates picks across sessions and bins; it must be connected to preserve picks between runs.
Storage item for the corridor constraint picks used to guide auto-picking. Define the acceptable η range at each time by picking the corridor boundaries interactively.
Optional mute pick item defining a stretch mute to be applied to CIGs before semblance analysis. Connect to suppress NMO-stretch artefacts at shallow times.
Controls trace sorting before semblance computation. Default: As is. Select Offset if the input CIGs are not already sorted by offset to ensure correct moveout analysis.
Container grouping all semblance computation and auto-picking parameters.
Near-surface reference velocity (m/s) used in the VTI moveout equation. Default: 1800 m/s. Set to the average velocity of the shallow section to ensure accurate η-to-moveout mapping.
Minimum η value in the semblance scan. Default: -2. In most geological settings η is positive (0 to 0.3), but negative values are included by default to accommodate unusual anisotropy. Narrow this range to the expected geologically realistic interval to improve display resolution.
Maximum η value in the semblance scan. Default: 2. Reduce to the expected maximum anisotropy for your lithology to sharpen the semblance panel and speed up computation.
Increment of η between adjacent semblance columns. Default: 0.01. Smaller steps give finer resolution in the semblance panel but increase computation time. Values of 0.01–0.05 are typical for production workflows.
Length (s) of the time-smoothing window applied to the semblance panel to reduce noise. Default: 0.05 s. Increase on noisy data to produce a smoother, more interpretable semblance display.
Maximum NMO stretch fraction (0–1) permitted before a sample is muted. Default: 0.5 (50%). Samples stretched beyond this ratio are excluded from the semblance computation and the output stacks.
Time window (s) used to normalise the semblance. Default: 0.1 s. This controls the temporal extent over which energy is summed before normalisation. A longer window reduces the sensitivity of the semblance to individual events.
Start time (s) of the window within which the auto-picker searches for the peak η semblance. Default: 0.04 s. Set to the shallowest time from which η picking is geologically meaningful.
End time (s) of the auto-picking window. Default: 1.5 s. Set to the deepest time of interest.
Time interval (s) between successive auto-pick control points along the time axis. Default: 0.4 s. Reduce for a denser, more detailed η function; increase for a sparse but robust pick.
Trace (bin) interval at which the auto-picker runs across the survey. Default: 50 bins. Reduce for a denser spatial coverage of η picks.
Minimum semblance value (0–1) required for an auto-pick to be accepted. Default: 0.5. Bins with peak semblance below this threshold are not picked. Increase on noisy data to accept only high-confidence picks.
When enabled, the auto-picker fits a polynomial approximation to the semblance peak for sub-sample η resolution rather than taking the discrete maximum. Default: off. Enable when Step eta is coarse and you need finer interpolated η values.
Degree of the polynomial used for the semblance peak approximation when Use approx for auto picking is enabled. Default: 5. Higher degrees fit more complex peak shapes but risk overfitting on noisy semblance panels.
Number of neighbouring bins included on each side when forming a super-gather for semblance analysis. Default: 0 (no super-gather). Increase to improve semblance quality on sparse or noisy data by summing traces from adjacent bins before computing semblance.
When enabled, a spatial smoothing filter is applied to the auto-picked η function after picking to reduce lateral scatter. Default: off. Enable when auto-picks show high spatial variability on a geologically smooth anisotropy field.
Time window (s) used to smooth the auto-picked η function along the time axis. Default: 0.05 s. Active when Use smooth for auto picking is enabled.
When enabled (default), the auto-picker is constrained to search only within the corridor defined by the ETA corridor picking item. This prevents picks from jumping to distant semblance artefacts and is strongly recommended on production datasets.
Half-width (in η units) of the corridor window created when the user clicks on the semblance panel to define a corridor pick. Default: 0.3. Increase to create a wider corridor that tolerates more variation in the η function.
When enabled (default), the mute pick connected to the Mute picking item input is applied to the gathers before semblance analysis. Disable when no mute is needed.
When enabled (default), traces are shifted to the datum defined by Output datum before stacking. Disable when the input data is already at the desired datum.
Reference datum depth (m) to which output stacks are shifted when Shift datum is enabled. Default: 0 m. Set to the processing datum used for the PSTM migration.
Container controlling how data is read from disk during the Create output stacks action.
Number of bins read simultaneously from the SEG-Y file during the bulk stack output operation. Default: 1000 bins. Reduce if memory is limited; increase to improve I/O throughput on fast storage.
Standard SEG-Y reading parameters (byte positions for trace headers, sample format, etc.) inherited from the project SEG-Y configuration.
Selects processing device. GPU can accelerate semblance computation on large surveys.
Configuration for distributed (cluster) execution.
Minimum number of gathers sent per work chunk during distributed execution.
When enabled, restricts CPU thread count per cluster node to the value in Number of threads.
Optional text appended to the distributed job name.
When enabled, applies the CPU affinity mask specified in Affinity.
CPU affinity mask applied when Set custom affinity is enabled.
Maximum number of CPU threads used during execution.
When enabled, this module is bypassed and data passes through unchanged.
The currently selected CIG without η correction applied. Used for before/after comparison with the Selected gather applied output.
The currently selected CIG with the picked η correction applied. Compare to the Selected gather to assess the effectiveness of the anisotropy correction.
The selected CIG with the mute applied but without η correction.
The selected CIG with both the mute and the η correction applied. This is the final processed gather for display.
The selected gather with the η correction applied and NMO removed (inverse NMO), showing the pre-NMO gather with anisotropy compensated.
Inline stack section without η correction. Connect to a display module for before/after comparison.
Crossline stack section without η correction.
Inline stack section with η correction applied. This is the preferred output for final display and interpretation after satisfactory η picking.
Crossline stack section with η correction applied.
Removes all η picks from all bins. Use before re-running autopicking with updated parameters.
Saves the current η picks to the ETA picking item for persistence between sessions.
Loads previously saved η picks from the ETA picking item.
Runs the automatic η picker for the currently selected bin only. Use for interactive QC before running on the full dataset.
Runs the automatic η picker across all bins in the survey.
Applies the picked η function to all CIGs and writes the corrected gathers to the output SEG-Y file. Run after satisfactory picking to produce the final η-corrected gather dataset.
Generates inline and crossline stack sections from the η-corrected gathers. Run after Create eta applied gathers to produce the final stacked volume.
Clears all mute picks from the mute picking item.
Saves the current mute picks to the mute picking item for persistence.
Loads previously saved mute picks from the mute picking item.
Clears all corridor constraint picks from the ETA corridor picking item.
Saves the corridor constraint picks for reuse in future sessions.
Loads previously saved corridor constraint picks.