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<< Click to Display Table of Contents >> Navigation: Migration > Anizo Kirchhoff PreSTM - 2D/3D |
Performs anisotropic Kirchhoff pre-stack time migration (PreSTM) for both 2D and 3D surveys, producing offset- and azimuth-sorted Common Image Gathers (CIGs) written directly to an output SEG-Y file. The migration uses a Vrms velocity model and applies the Kirchhoff integral operator with anti-aliasing, an optional stretching-factor correction, and a configurable aperture. GPU acceleration is supported when available. The module can resume from a previous partial run, making it suitable for large 3D datasets processed in distributed environments.
Use this module after velocity analysis to generate migrated CIGs for subsequent AVO/AVAZ analysis or stack. For isotropic data or simpler workflows, consider the standard Kirchhoff PreSTM module. Note: this module is flagged as deprecated in the software; it may be superseded by a newer migration implementation in future versions.
The SEG-Y file handle providing read access to the prestack seismic data. All traces to be migrated are accessed through this connection. The data must already be sorted according to the connected sorted headers dataset.
The sorted trace header index that defines the gather order for migration. This dataset must be consistent with the connected SEG-Y data handle and contain all geometry information (source/receiver coordinates, offsets) needed to compute traveltimes.
The root-mean-square (Vrms) velocity model used to compute Kirchhoff traveltimes. The model is sampled on the output CMP grid. Velocity accuracy directly affects the quality of focusing and the positioning of reflectors in the migrated image.
Trace header dataset that defines the output CMP grid geometry — the set of CMP locations at which migrated CIGs will be produced. Connect the geometry from your binning or geometry assignment module.
Selects whether the migration runs in 2D or 3D mode. In 3D mode additional inputs (BinGrid, 3D grid definition) become active.
Optional group of advanced 3D parameters. Expand this section to access fine-grained control over the 3D migration grid and operator settings.
Toggle to enable manual definition of the 3D output CMP grid. When enabled, the CMP Interval Along Inline and CMP Interval Along Xline parameters are used instead of values derived from the BinGrid.
The bin grid defining the spatial layout of the input seismic data in 3D mode. Used to map input trace coordinates to the CMP grid for the migration operator.
The bin grid for the Vrms velocity model in 3D mode. May differ from the input data BinGrid if the velocity field was built on a coarser grid. The module interpolates velocity values onto the output CMP grid as needed.
Full path and filename for the output SEG-Y file that will contain the migrated CIGs. The file is created (or overwritten) at the start of the run. Ensure sufficient disk space is available; 3D CIG volumes can be very large.
The smallest source-receiver offset (m) included in the output CIGs. Traces with offsets below this value are not migrated into the output. Default: 0 m. Increase to exclude near-offset data affected by noise or muting.
The largest source-receiver offset (m) included in the output CIGs. Traces with offsets above this value are excluded. Default: 3000 m. Set to match the maximum useful offset in your acquisition geometry.
The offset bin width (m) for the output CIGs. All input traces within each offset bin are summed into a single output trace. Default: 50 m. Smaller values produce higher offset resolution but lower fold per bin and larger output files.
Minimum source-receiver azimuth (degrees) for azimuth-sector CIG output. Azimuths are folded to the range 0–180° before binning. Default: 0°. Set equal to Azimuth max to disable azimuth sectoring and produce offset-only CIGs.
Maximum source-receiver azimuth (degrees) for the output azimuth sectors. Default: 0°. For AVAZ analysis, set to 180° and choose an appropriate Azimuth increment (e.g., 30° or 45°).
The azimuth bin width (degrees). The number of azimuth sectors equals (Azimuth max − Azimuth min) / Azimuth increment. Default: 50°. Smaller increments improve azimuthal resolution at the cost of lower fold per sector and larger output volumes.
The maximum lateral migration radius (m) around each output CMP. Traces farther than this distance from the output CMP are excluded from the migration sum. Default: 3000 m. A larger aperture improves imaging of steeply dipping reflectors but increases computation time. When Use full CMP Aperture is on, this parameter is overridden.
When enabled, the migration aperture is automatically set to include all available CMP traces regardless of distance, overriding the Aperture parameter. Default: on. Disable to restrict the aperture using the Aperture parameter, which can significantly reduce runtime on large 3D surveys.
Enables GPU acceleration for the Kirchhoff traveltime computation and summation. Default: off. Requires a CUDA-capable GPU and the appropriate GPU execution environment. When enabled, processing speed is typically several times faster than CPU-only mode for large 3D datasets.
An additional lateral padding (m) added to the main Aperture to include traces from adjacent CMPs that may contribute energy to the current output location. Default: 0 m. Increase slightly if you observe edge effects at the boundary of the migration aperture.
When enabled, applies a stretch correction to compensate for NMO-related waveform distortion (stretch) at large offsets. Default: off. Enable in conjunction with the Stretching Factor parameter when high-offset data shows significant frequency distortion.
The stretch mute threshold (%). Samples where the NMO stretch exceeds this percentage are zeroed in the output. Active only when Use Stretching Factor is enabled. Default: 0%. Typical values are 20–50%. Lower values apply a more aggressive mute.
The near-surface replacement velocity (m/s) applied to the uppermost part of the velocity model. Default: 1500 m/s. Set to match the weathering-layer velocity in your area to ensure correct shallow migration.
Controls the strength of the anti-aliasing filter applied during the Kirchhoff summation to suppress spatial aliasing artefacts. Higher values apply stronger anti-aliasing. Reduce if the migration is over-smoothing steep dips; increase if aliasing noise is visible in the CIGs.
The maximum frequency (Hz) used in the rho (ρ) filter, which is the derivative operator applied as part of the Kirchhoff imaging condition. Default: 120 Hz. Set to match the highest frequency present in your data. Frequencies above this value in the rho filter are tapered to zero.
The maximum dip angle (degrees) considered during the migration aperture calculation. Reflections arriving from angles steeper than this value are excluded from the summation. Default: 90° (no dip limit). Reduce to suppress steep-dip noise at the cost of potentially missing steep structure.
A scalar multiplier applied uniformly to the Vrms velocity model before migration. Default: 1.0 (no scaling). Values greater than 1.0 over-migrate; values less than 1.0 under-migrate. Useful for quick sensitivity tests without modifying the velocity model itself.
The CMP spacing (m) along the inline direction for the 3D output grid. Active only when 3D grid define is enabled. Default: 12.5 m. Set to match your survey's bin size in the inline direction.
The CMP spacing (m) along the crossline direction for the 3D output grid. Active only when 3D grid define is enabled. Default: 25.0 m. Set to match your survey's bin size in the crossline direction.