|
<< Click to Display Table of Contents >> Navigation: MultiFocusing > Migration Imaging - 2D ZO-MF |
Note: This module is deprecated. It is preserved for compatibility with older processing flows and may be removed in a future release. For new projects, use the current Multi-Focusing migration workflows.
Migration Imaging - 2D ZO-MF performs Zero-Offset Multi-Focusing (ZO-MF) migration imaging along a 2D seismic line. The module reads a pre-computed Multi-Focusing wavefield database (storage file), then applies Kirchhoff-type time migration to each bin location to produce a focused, migrated image stack. Multi-Focusing analysis compresses the seismic wavefield using an operator that accounts for both the normal-incidence ray and the emerging wavefront curvature, resulting in improved spatial resolution and coherent signal stacking compared to conventional CMP migration.
For each bin in the line, the module retrieves the MF wave collection from the storage file, selects the contributions that fall within the specified angle corridor and correlation quality thresholds, and migrates those contributions using a beam-forming Kirchhoff operator. The resulting migrated traces are assembled into an image stack gather for further interpretation or export to SEG-Y.
Typical workflow: run the Multi-Focusing geometry and engine modules first to populate the 2D storage database, then use this module to transform the MF results into a migrated time-domain image.
The path to the 2D Multi-Focusing storage database file (*.kdb). This file is created by the upstream MF Engine module and contains the pre-computed wavefield attributes (wave collections, geometry, time quantization table) for every bin along the 2D line. The module opens this file in read-only mode and uses its contents as the sole input for the migration calculation. The file must be a valid, fully computed MF database — bins flagged as not yet calculated are skipped automatically during processing.
This parameter group controls the core migration engine settings: velocity model, spatial aperture, beam tapering, and frequency/angle limits. Together these parameters define the operator used to focus each bin's wavefield contributions into a migrated trace.
The interval velocity model (as a gather) used to compute the Kirchhoff migration travel-times. This velocity field is applied bin-by-bin and sample-by-sample: the values are scaled by the Velocity Factor before being used. Provide an RMS or interval velocity gather covering the entire line and the full time range of the data. An accurate velocity model is critical for correct event positioning in the migrated image; errors will cause under- or over-migration artifacts.
The maximum lateral migration aperture in metres (default: 3000 m). This defines how far from each output bin location the algorithm searches for contributing traces. A wider aperture allows steeply dipping events to be properly imaged but increases computation time and may introduce migration noise from distant, low-amplitude contributions. For shallow targets with moderate dips, reduce the aperture to improve efficiency. As a rule of thumb, set the aperture to at least the depth of the target divided by the tangent of the steepest expected dip.
The width of the beam (Gaussian taper half-width) applied across the migration aperture in metres (default: 300 m). The beam aperture controls how sharply the migration operator is tapered at its edges. A narrower beam concentrates the migration energy near the operator apex and suppresses contributions from the aperture edges, reducing migration noise but potentially attenuating steeply dipping energy. A wider beam uses more of the full aperture with a gentler taper, preserving dip fidelity at the cost of slightly more migration swings. Adjust this parameter together with Beam Power to fine-tune the lateral roll-off shape.
The exponent controlling the shape of the beam taper function (default: 1). Higher values produce a steeper, more box-like roll-off at the beam edges, concentrating the migration energy more tightly and suppressing edge effects more aggressively. A value of 1 gives a linear (cosine-like) taper. Increasing this value to 2 or 4 makes the taper increasingly abrupt. Use higher values when migration smiles or edge artefacts are visible in the output image.
The near-surface replacement velocity in m/s (default: 1500 m/s). This is the velocity assumed for the shallow layer above the datum, used to compute the datum shift correction and to initialise the CRE (Common Reflection Element) radius calculation for the migration operator. Set this value to the average velocity of the weathering layer or the velocity immediately below the base of the LVL (Low Velocity Layer). For marine data, use the water velocity (~1480–1520 m/s). An incorrect replacement velocity will introduce a systematic time shift in the migrated result.
The maximum frequency in Hz used in the migration operator (default: 100 Hz). The migration band-pass anti-alias filter is designed with this cutoff, and the operator taper width scales accordingly (a 10% cosine taper is applied from 0.9 × Max Frequency to Max Frequency). Set this value to match the highest usable signal frequency in your data. Setting it too high introduces high-frequency noise into the migrated image; setting it too low unnecessarily sacrifices vertical resolution.
A scalar multiplier applied to the entire Input Velocity model before migration (default: 1.0). All velocity values in the input gather are multiplied by this factor prior to computing migration operators. This provides a quick way to explore the effect of velocity uncertainty: use a value slightly above or below 1.0 (e.g., 0.95 or 1.05) to test sensitivity without editing the velocity gather itself. Leave at 1.0 for standard production migration.
The maximum migration dip angle in degrees (default: 90°). The migration operator is restricted to ray paths that arrive at angles less than this value measured from the vertical. Reducing this angle limits the aperture to near-vertical ray paths, which suppresses steeply dipping noise and migration artefacts but may clip the flanks of steeply dipping reflectors. For most land and marine datasets with dips up to 30–45°, values between 45° and 60° are appropriate. Use the full 90° only when very steep dips must be preserved.
This group controls how the MF wave contributions are selected and filtered before migration. The parameters define the dip/angle corridor accepted for stacking and the minimum quality thresholds required for a contribution to be included. Tightening these parameters improves coherent noise suppression at the cost of fold reduction.
The number of independent dip directions used in the wave-selection stacking (default: 1, minimum: 1). In 2D processing this is typically left at 1 since there is only a single inline direction. Increasing this value allows the algorithm to simultaneously consider multiple dip azimuths, which can be useful when data contains crossing dips or diffractions from multiple directions. For standard 2D acquisition keep this at 1.
The lower bound of the dip-angle corridor accepted for stacking, in degrees (default: -90°, range: -90° to +90°). Only MF wave contributions whose dip angle is equal to or greater than this value are included in the migration stack. Together with ToAngle, this defines a symmetrical or asymmetrical angular gate. Setting FromAngle to 0° and ToAngle to +90° will use only up-going (forward-dipping) contributions; using the full range -90° to +90° includes all dips.
The upper bound of the dip-angle corridor accepted for stacking, in degrees (default: +90°, range: -90° to +90°). Only MF wave contributions whose dip angle is equal to or less than this value are included. Use this parameter in conjunction with FromAngle to restrict migration to a specific range of dipping events, for example to focus on flat-lying reflectors (e.g., -5° to +5°) or to exclude a known noise dip direction.
The minimum MF correlation coefficient (coherency score) required for a wave contribution to be included in the migration stack, expressed as a percentage (default: 10%, range: 0–100%). The MF engine assigns each wave a correlation quality measure. Contributions with a score below this threshold are discarded as incoherent noise. Increasing the threshold selects only the highest-quality, most coherent wavefield contributions, improving the signal-to-noise ratio of the migrated image but reducing effective fold. Start with 10–20% and adjust based on the coherency distribution of your data.
The minimum angular separation (in index units) between accepted wave contributions in the angle domain (default: 1, minimum: 1). This parameter prevents multiple nearly identical wave solutions (which would correspond to very similar dip angles) from being stacked together and artificially dominating the output. Increasing this value enforces greater angular diversity among the selected contributions. Use a value of 1 for standard processing; increase it if you observe correlated stripping artefacts in the migrated image caused by clustered, near-duplicate wave solutions.
The minimum separation (in index units) between accepted wave contributions in the CRE radius domain (default: 100, minimum: 1). The CRE (Common Reflection Element) radius characterises the curvature of the emerging wavefront. This threshold prevents solutions with nearly identical curvatures from being over-represented in the stack, promoting diversity in the selected wave contributions. Increase this value if the migrated output shows residual ringing or over-stacking artefacts attributable to redundant CRE-radius solutions.
This group controls how the migrated image is displayed in the interactive viewer. The parameters allow you to apply a datum shift to the on-screen display without modifying the exported data.
The reference datum elevation in metres (default: 0 m) used for the interactive display datum shift. When Shift To Datum is enabled, the migrated image displayed in the viewer is shifted in time so that the zero-time reference corresponds to this datum level. This parameter affects only the visualization and does not change the data written to the output gather or exported to SEG-Y.
When enabled (default: off), the migrated image in the interactive viewer is shifted to the reference datum specified in the Datum parameter above. Enable this toggle to view the migration result referenced to a flat datum, which can make it easier to compare the output with other datasets that have been datum-corrected. This is a display-only option and does not alter exported data.
This group selects which output image type is computed and stored. Currently the only available output type is the migrated stack.
When enabled (default: on), the module computes and outputs the migrated image stack gather. This is the primary output of the module — a time-domain seismic image formed by summing the selected, migrated MF wave contributions across all bins. Leave this enabled for standard use. Disabling it will suppress computation of the migrated stack output.
This group controls how the migrated image and associated parameter data are formatted and written during the Export params to sgy custom action. These settings apply to the SEG-Y output file produced by that action.
Controls whether the export overwrites an existing file or appends to it (default: Direct). Direct creates a new file or overwrites an existing one. Append adds the exported traces to the end of an existing SEG-Y file, which is useful when processing a long line in segments and combining the results into a single output file.
When enabled (default: off), coordinate values written to the SEG-Y trace headers are converted from metres to feet. Enable this option only when the output SEG-Y file must conform to a project convention that uses imperial units. All internal calculations remain in metres regardless of this setting.
When enabled (default: off), velocity trace samples with a value of zero are suppressed in the exported SEG-Y output. Some downstream interpretation applications misinterpret zero-valued velocity samples as missing data or as zero velocity. Enable this flag to replace zero velocity values with a non-zero placeholder or to skip them during export, avoiding potential loading errors in those applications.
When enabled (default: off), the exported traces are padded with zeros to fill the full record length defined in the SEG-Y header. Enable this option when the output SEG-Y file needs to conform to a fixed record length that is longer than the actual migrated data, for example when the output must be concatenated with data files that have a longer time window.
When enabled (default: off), the exported SEG-Y traces are time-shifted so that their zero-time reference corresponds to the export Datum elevation. This applies a static datum correction to all output traces before writing. Use this option when the migrated image must be delivered datum-referenced (e.g., to sea level or to a project reference plane) rather than referenced to the acquisition surface. Enable together with the Datum (export) parameter below.
The reference datum elevation in metres used for the export datum shift. When Shift to datum (export) is enabled, all output traces are shifted in time to reference this elevation. Set this to the project datum (e.g., mean sea level = 0 m, or a project-specific floating datum). This value is independent of the Datum parameter in the Visualization group, which affects only the interactive display.
Triggers the export of the migration parameters and/or the migrated image stack to a SEG-Y file, using the settings defined in the Export Params group. Run this action after the main migration calculation has completed to save the output in SEG-Y format for use in third-party interpretation or processing software. The Write mode, datum shift, unit conversion, and padding options in Export Params all apply to this export.