Description
The Merge velocity gathers module combines multiple velocity gathers — typically from individual 2D seismic lines or differently oriented acquisition azimuths — into a single unified 3D velocity cube. Each input gather is assigned a name, and the module spatially interpolates the velocity values from all inputs onto a common output grid, producing a continuously populated velocity volume that can be used for depth conversion, migration, or further velocity analysis.
The output grid can be defined either by an existing crooked line geometry or by specifying full bin grid parameters manually. The module supports both time-domain and depth-domain velocity gathers, and offers four spatial interpolation methods: ABOS (Adaptive B-spline On Smooth), Kriging, Voronoi, and Triangulation. Azimuth filtering allows selective merging of lines within a desired orientation range. The merged velocity cube can be saved to a GSD file and/or passed as an in-memory gather to the next processing step.
Two options: 3D cube extrapolation and depth velocity merge
Input DataItem:
Input Gather - input velocity 3D cube that was loaded (to RAM) as seismic gather data set.
Input DataItem
The primary input data connection. Connect the seismic gather (velocity volume) from the project that will serve as an additional source for the merge. This item is used alongside the named gathers defined in the Input gathers collection below.
Input crooked line
An optional crooked line geometry item that defines the output bin positions when Output geometry is set to By input crooked line item. The output velocity cube will be populated at the bin locations carried by this crooked line, preserving the original survey geometry. If you prefer to define the output grid manually, set Output geometry to By grid definition and this input is not required.
Interpolation container
Interpolation container
This group of parameters controls the spatial interpolation method used to fill the output velocity cube from the scattered input gather locations. All parameters in this group interact — only the parameters relevant to the chosen interpolation type are active at a time.
Interpolation type
Selects the algorithm used to interpolate velocity values from input gather positions to the output grid nodes. Available options are:
ABOS (default) — Adaptive B-spline On Smooth. A smooth, continuous interpolation method that works well for irregularly sampled data. When selected, use the Abos step parameter to control the spatial resolution of the underlying interpolation grid.
Kriging — Geostatistical interpolation that accounts for spatial correlation structure. Useful when input lines are sparse and structural trends must be honored. Requires setting the Kriging covariance type, Kriging range, and Kriging number of points.
Voronoi — Nearest-neighbor interpolation. Each output bin is assigned the velocity of the nearest input trace. Fast and preserves exact input values; no smoothing.
Triangulation — Linear interpolation using Delaunay triangulation of input points. Provides smooth linear transitions between input locations; a good balance between Voronoi and Kriging.
Kriging covariance type
Active only when Interpolation type is set to Kriging. Specifies the mathematical model that describes how spatial correlation between velocity values decays with distance. Options are Gaussian, Exponential, and Spherical. The Gaussian model produces the smoothest interpolation, the Spherical model is the most commonly used in geostatistics, and the Exponential model decays more rapidly with distance, making it suitable for abruptly varying velocity fields.
Kriging range
Active only when Interpolation type is set to Kriging. Defines the spatial correlation length in meters — the maximum distance at which input velocity traces are considered correlated and therefore influence each other during interpolation. Set this to approximately the typical spacing between seismic lines. The default value is 50000 m. Increasing this value smooths the output over larger areas; decreasing it makes the interpolation more locally constrained.
Abos step
Active only when Interpolation type is set to ABOS. Controls the cell size in meters of the intermediate regular grid used internally by the ABOS algorithm. Smaller values produce a finer intermediate grid, capturing more local velocity detail but requiring more computation. Larger values smooth over local variations, which is desirable when input lines are few and widely spaced. Default: 250 m. As a starting point, set this to approximately the average distance between input lines.
Kriging number of points
Active only when Interpolation type is set to Kriging. Specifies how many nearby input traces are used when estimating the velocity at each output grid node. Using more points improves stability but increases computation time. The default is 20. For sparse datasets, lower values may be needed if insufficient neighbors exist near some output nodes.
Input gathers
A collection of named velocity gathers to be merged into the output cube. Each entry in this list consists of a Name (a label for the line or dataset, used in on-screen display and azimuth visualization) and a Gather (a velocity gather data item). Add as many entries as you have input lines or datasets. The bin positions of all input gathers are displayed on the 2D location map and used to drive spatial interpolation. After adding or changing input gathers, use the Auto detect data params and Auto detect bin grid params custom actions to automatically populate the output grid and data parameters.
Datum - datum for Vint, usually max of elevations or above the relief surface.
The reference elevation level used to align depth-domain interval velocity gathers before merging. This is typically set to the maximum surface elevation across the survey area, or to a flat datum plane above the topographic relief. All input gathers are shifted to this common datum before interpolation, ensuring that velocity values at equivalent depths are correctly combined. This parameter is only relevant when working in the depth domain with topography-referenced input gathers.
Output geometry
Output geometry
Determines how the output velocity cube bin positions are defined. Two options are available:
By input crooked line item — The output bin grid is taken directly from the crooked line connected to the Input crooked line data item. Use this option when you want the output to follow an existing 2D or crooked 3D survey geometry.
By grid definition — The output grid is defined explicitly using the parameters in the Grid definition group. Use the Auto detect bin grid params action to automatically compute these values from the input data geometry.
Grid definition
Grid definition
This group of parameters manually specifies the output bin grid geometry. These parameters are active when Output geometry is set to By grid definition. Use the Auto detect bin grid params custom action to populate these parameters automatically from the loaded input gathers.
Inline bin spacing
The distance in meters between adjacent output bins in the inline direction. This determines the lateral resolution of the output velocity cube along the inline axis. Default: 50 m. Reduce this value to produce a denser output grid; increase it to reduce the number of output traces. The Auto detect bin grid params action estimates an appropriate value from the average trace spacing in the input gathers.
Crossline bin spacing
The distance in meters between adjacent output bins in the crossline direction. Default: 50 m. This controls the lateral resolution of the output velocity cube along the crossline axis. Typically set equal to or larger than the inline bin spacing for 3D surveys.
Grid starting point X coord
The X coordinate (Easting) in meters of the origin corner of the output bin grid. Together with the Y coordinate, this defines the physical location of the first bin. Default: 0. The Auto detect bin grid params action sets this automatically from the bounding box of all input gather positions.
Grid starting point - Y coord
The Y coordinate (Northing) in meters of the origin corner of the output bin grid. Default: 0. Populated automatically by Auto detect bin grid params.
Inline azimuth
The azimuth angle in degrees of the inline direction of the output grid, measured clockwise from East. This defines the orientation of the output bin grid. For a North-South inline direction, set to 90 degrees. Populated automatically by Auto detect bin grid params based on the dominant orientation of input gather positions.
First inline number
The inline number assigned to the first (origin) row of the output grid. This is used for labeling output traces with inline header values. Set to match the inline numbering convention of your project. The Auto detect bin grid params action will estimate a starting value.
First crossline number
The crossline number assigned to the first column of the output grid. Used for labeling output traces with crossline header values. Set to match the crossline numbering convention of your project.
InLine distance
The total spatial extent of the output grid in the inline direction, in meters. This defines how far the grid extends along the inline axis from the starting point. Default: 10000 m. Together with the inline bin spacing, it determines the total number of output inline bins. Populated automatically by Auto detect bin grid params to enclose all input gather positions.
Crossline distance
The total spatial extent of the output grid in the crossline direction, in meters. Default: 10000 m. Together with the crossline bin spacing, it determines the total number of output crossline bins. Populated automatically by Auto detect bin grid params to enclose all input gather positions.
Angle between inline and crossline
The angle in degrees between the inline and crossline axes of the output grid. Default: 90 degrees, which produces a standard orthogonal grid. For surveys with non-orthogonal acquisition geometry, this can be adjusted to match the actual grid shape. Valid range: -360 to 360 degrees.
Processing parameters
Data length
The total data length of the output velocity cube. When working in the Time domain this is specified in seconds (default: 5.0 s); when working in the Depth domain this is specified in meters (default: 5000 m). The correct field is shown automatically based on the Input gathers domain selection. Use the Auto detect data params action to read this value from the input gathers automatically.
Sample rate
The sample interval of the output velocity cube. When working in the Time domain this is in seconds (default: 0.002 s = 2 ms); when working in the Depth domain this is in meters (default: 10 m). All input gathers are resampled to this rate before interpolation. The Auto detect data params action reads the finest sample rate from all input gathers and sets it here automatically.
Decimation factor
Reduces the number of input traces contributed from each input gather by keeping every N-th trace, where N is this value. Default: 1 (no decimation — all traces are used). Increase this value to speed up processing when input gathers are very densely sampled and only a coarser representation is needed for merging. For example, a decimation factor of 4 uses every 4th trace from each input gather.
Remove zero velocity traces
When enabled, traces in which any sample has a velocity value below 0.1 m/s are treated as empty and removed from the input before interpolation. Default: off. Enable this option to exclude unfilled or placeholder traces that would otherwise contribute spurious zero-velocity values to the interpolated output cube.
Output filename
The path and filename for the output GSD velocity file. The merged velocity cube will be saved to this file on disk. Specify a file with a .gsd extension. Either this field or Create output gather (or both) must be specified for the module to produce output.
Create output gather
When enabled, the merged velocity cube is also stored in memory as an output gather data item, making it immediately available to downstream modules in the processing flow without requiring a file read step. Default: off. Enable this when you want to pass the merged velocity cube directly to a subsequent module such as depth conversion or migration. Note that large velocity volumes may require significant RAM when this option is active.
If you have any questions, please send an e-mail to: support@geomage.com