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The Velocity Selector - Kirchhoff PreSTM Engine is the computation engine component of the Kirchhoff pre-stack time migration velocity analysis workflow. It reads pre-stack seismic traces, applies the Kirchhoff migration operator, and writes partial migration images to a keyed velocity-selector storage database (KDB file) for multiple velocity factor trials simultaneously. The resulting database can then be interrogated interactively to pick optimal migration velocities at each CMP location.
This module is designed to be used as a sub-procedure called by the Kirchhoff PreSTM migration module when its Storage type is set to Velocity selector 2D or Velocity selector 3D. It handles the inner migration loop for a given velocity factor, writing results to the shared KDB storage. Users interact with the parent migration module rather than with this engine directly.
Path to the KDB velocity selector database file where this engine writes its migration results. The parent migration module creates and manages this file; the engine appends its output to it. This file is subsequently used for interactive velocity picking in the Kirchhoff velocity selector module.
Handle to the input pre-stack seismic data. The engine reads traces directly from this SEG-Y file using the sorted header index to locate the relevant gathers for each output CIG.
Pre-sorted gather index vector derived from the seismic trace headers. This index allows the engine to efficiently locate the input traces needed for each output bin without scanning the full SEG-Y file.
The base RMS velocity model used for migration. The engine scales this model by the VelFactor value passed from the parent module to produce the trial velocity for each migration pass.
VTI anisotropy parameter model. Required when VTI anisotropic migration is enabled in the parent module.
Spatially varying near-surface velocity map used to refine the shallow velocity model. Used when Use Vrms map is enabled.
Dimensionality of the migration operator. 2D applies a line-source migration operator suitable for 2D surveys. 3D applies a point-source operator for full 3D surveys. 2.5D is a 2D operator with 3D geometric spreading correction, suitable for 2D lines acquired in a 3D earth. The default is 2D.
Minimum source-receiver offset in metres included in the output CIG (default: 0 m). Traces with offsets below this value are excluded from migration.
Maximum source-receiver offset in metres included in the output CIG (default: 3000 m). Traces beyond this offset are excluded.
Offset bin size in metres for the output CIG (default: 50 m). Smaller increments produce finer offset resolution but larger output data.
Maximum migration aperture radius in metres (default: 3000 m). Traces within this lateral distance of each output bin are summed during migration. Set this to balance image quality against computation time.
Selects whether the aperture is constant with time or defined by the time-variant table. Time variant mode allows a smaller aperture in the shallow section and a larger one at depth.
Table of (time, aperture) pairs for time-variant aperture mode. The aperture is linearly interpolated between rows as a function of two-way travel time.
When enabled, the aperture distance is measured along the 2D acquisition line in picket units rather than in metres. Suitable for 2D crooked-line surveys.
Additional lateral taper distance in metres applied at the aperture boundary to reduce edge effects. Set to zero to disable the taper.
When enabled, applies an NMO stretch mute during migration. Portions of traces where the NMO correction stretches the wavelet beyond the Stretching Factor threshold are excluded from the summation.
NMO stretch mute threshold as a percentage (default: 0%). Active only when Use Stretching Factor is enabled. A value of 50% mutes portions where NMO stretch exceeds 50%.
Near-surface replacement velocity in m/s (default: 1500 m/s) used to compute static corrections from the acquisition surface to the datum. Must match the value used in the static corrections applied to the data.
Scaling coefficient for the anti-aliasing filter. Higher values reduce anti-aliasing strength, preserving more high-frequency content. Adjust if high-frequency noise or spatial aliasing is observed in the output CIGs.
Maximum frequency in Hz for the Rho (derivative) filter applied during migration (default: 120 Hz). This limits the bandwidth of the migration operator and should match the maximum usable signal frequency in the data.
Maximum dip angle in degrees (default: 90°) limiting the migration operator. Traces arriving at angles beyond this value are excluded, suppressing steeply dipping noise. Reducing this value attenuates steep-dip artefacts and migration smiles in the CIGs.
When enabled, the spatially varying V0 Map is used to refine the near-surface velocity model. Enable this when applying laterally varying near-surface corrections.
CMP spacing in the inline direction in metres (default: 12.5 m), used by the anti-aliasing operator. Set this to match the actual inline CMP interval of the survey.
CMP spacing in the crossline direction in metres (default: 25.0 m). Set this to match the actual crossline CMP interval.
Enables VTI anisotropic Kirchhoff migration. When active, the Input VTI model must be connected and Thomsen anisotropy parameters are incorporated into travel-time computation.
Parameter group for advanced 3D grid definition options, allowing explicit specification of input and velocity data bin grids and output geometry when the standard automatic grid detection is insufficient.
When enabled, the 3D bin grid inputs below (Input data BinGrid, Velocity data BinGrid, Output geometry) are used to explicitly define the spatial grids, overriding the automatic grid detection.
3D bin grid describing the geometry of the input seismic data. Used when 3D grid define is enabled.
3D bin grid describing the geometry of the velocity model. Used when 3D grid define is enabled. May differ from the input data bin grid if the velocity model was built on a different grid.
2D bin point vector defining the output image grid positions. Used when 3D grid define is enabled to override the automatic grid.
Parameter group defining the velocity factor sweep range for this engine instance. The engine iterates over all factor values from Min VelFactor to Max VelFactor in steps of VelFactor Step, producing one migration output per factor.
Minimum velocity factor for the scan (default: 0.8). The migration will be run at 80% of the base Vrms model at the lower end of the sweep.
Maximum velocity factor for the scan (default: 1.2). The migration will be run at 120% of the base Vrms model at the upper end of the sweep.
Increment between successive velocity factor trials (default: 0.1). Smaller increments provide finer velocity resolution at the cost of proportionally more computation. A step of 0.05 gives 9 migration trials between 0.8 and 1.2; a step of 0.1 gives 5 trials.
SEG-Y reading parameters (cache size, byte-swap settings) controlling access to the input SEG-Y file. Default values are appropriate for most SEG-Y files.
Selects CPU or GPU processing. GPU execution provides the largest speed improvement for Kirchhoff migration and is strongly recommended when NVIDIA GPUs are available.
Configuration for distributed cluster execution. The migration work is split across nodes; each node processes a subset of the output bins and writes its partial results to the shared KDB storage file.
Minimum number of output bins per distributed job chunk. Larger values reduce scheduling overhead at the cost of load-balancing flexibility.
Maximum number of CPU threads per compute node. Use this on shared cluster nodes to avoid monopolising all cores.
Optional text suffix for the distributed job name to distinguish it from other jobs on the cluster.
Enables manual CPU core affinity assignment. Leave disabled unless performance tuning on NUMA systems is required.
CPU core affinity mask. Only used when Set custom affinity is enabled.
Number of CPU threads for local (non-distributed) processing. Set to match available physical cores.
Parameter group for running external scripts before or after this engine executes.
Path to a script executed before migration starts.
Path to a script executed after migration completes.
When enabled, this module is bypassed without executing.