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<< Click to Display Table of Contents >> Navigation: Velocity > CreateVRMSByVFFunction |
Note: This module is deprecated. It is retained for compatibility with legacy processing flows. For new projects, consider using the current velocity scaling and editing tools available in g-Platform.
CreateVRMSByVFFunction scales a VRMS (root-mean-square velocity) gather by a time-varying velocity factor (VF) function supplied in an external ASCII text file. For each time sample, the module multiplies the velocity value in the gather by the corresponding factor read from the file. This allows systematic scaling of an existing velocity model — for example, to apply a calibration correction, account for anisotropy, or adjust velocities to match well data across the survey area.
The module supports three file formats: a simple 1D time-velocity factor curve (applied uniformly across all traces), or a spatially varying 2D factor field defined by either X/Y survey coordinates or inline/crossline bin numbers. In the spatially varying case, the factor at each trace location is determined by Kriging interpolation of the supplied data points. The VF function is read and pre-processed before the main execution begins, so the file must be accessible and correctly formatted before the module runs.
The input VRMS velocity gather (in the time domain) whose amplitude values represent velocity at each time sample and trace. This gather must have valid trace header geometry (bin coordinates or inline/crossline positions) assigned, as the spatial formats use these values to locate each trace within the VF factor field. If geometry has not been applied, run the appropriate binning or geometry assignment module before using this module.
Specifies the column layout of the VF ASCII input file. Three options are available:
Time-VF (default) — The file contains two columns: time (in seconds) and velocity factor. A single 1D curve is defined and applied identically to every trace in the gather. Use this option when the velocity scaling does not vary laterally across the survey.
Inline-Xline-Time-VF — The file contains four columns: inline number, crossline number, time (in seconds), and velocity factor. Each row defines a factor value at a specific bin location and time. The module uses Kriging interpolation to derive the factor at every trace position. Use this option for 3D surveys where the VF function varies by bin location.
X-Y-Time-VF — The file contains four columns: X coordinate, Y coordinate, time (in seconds), and velocity factor. Similar to Inline-Xline-Time-VF but uses survey Cartesian coordinates instead of bin numbers. Use this option when well control or correction points are defined in map coordinates rather than bin grid coordinates.
The full path to the ASCII text file (.txt) containing the velocity factor function. The file must be a plain space- or tab-delimited text file with columns matching the selected Format. Time values should be in seconds. Velocity factor values are dimensionless multipliers applied directly to the velocity samples — a factor of 1.0 leaves the velocity unchanged, values greater than 1.0 increase velocities, and values less than 1.0 decrease them. The file is read in full before processing begins, so it must be present and readable at execution time.
The number of neighboring data points used by the Kriging interpolator when computing the velocity factor at each trace location. Default: 15. This parameter is active only when using the spatially varying formats (Inline-Xline-Time-VF or X-Y-Time-VF). Higher values produce a smoother spatial interpolation at the cost of longer computation time; lower values run faster but may be less representative in areas of sparse data coverage. If the VF file contains fewer control points than this value, the interpolation will use all available points. For the Time-VF format, this parameter has no effect.
The scaled VRMS velocity gather, with the same geometry and sample interval as the input gather. Each velocity sample has been multiplied by the corresponding VF factor value (interpolated to the sample time and trace location). The output gather can be connected downstream to NMO correction, velocity analysis displays, or velocity conversion modules.