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<< Click to Display Table of Contents >> Navigation: Velocity > Vrms from Interval velocity by time tables |
This module computes a VRMS (root-mean-square velocity) model from an input interval velocity model using fast-marching ray tracing. Starting from an existing VINT (interval velocity) model — typically a refraction or depth model — the module shoots rays through the velocity field, integrates traveltimes, and constructs the corresponding VRMS field on a regular output grid. This converts a depth-domain velocity description into a time-domain VRMS model that can be used for NMO, semblance analysis, or as a starting model for tomographic inversion.
Use this module when you have a depth interval velocity model (for example from refraction tomography or well-log calibration) and need to generate a time-domain VRMS model for further processing. It is particularly useful for bridging depth-domain velocity models with time-domain workflows.
The input interval velocity model. This is typically a depth-domain VINT field from refraction tomography, well-log interpolation, or any other depth velocity source. The module traces rays through this model to compute the output VRMS.
The time sample interval (s) of the output VRMS model. The default is 0.004 s (4 ms). Match this to the sample rate of the seismic data with which the VRMS model will be used.
The number of time samples in the output VRMS model. The default is 500. The total output time length equals Output samples × Output sample rate. Increase this value if the deepest reflectors of interest exceed the default time window.
When enabled, the VRMS is computed using the Dix formula applied directly to the interval velocity model, bypassing the fast-marching ray tracing. This is faster but less accurate for complex velocity structures. The default is false (ray tracing is used). Enable this option when a quick approximate VRMS is sufficient.
Controls the verbosity of diagnostic output written during processing. Leave at the default value unless troubleshooting unexpected results.
When enabled, the module extracts the near-surface velocity (V0) map directly from the top of the input VINT model rather than using the constant V0 parameter. Enable this when the near-surface velocity varies laterally and the VINT model captures that variation. The default is false.
The near-surface interval velocity (m/s) used as the reference starting velocity for ray tracing. The default is 1500 m/s. This parameter is only used when Construct V0 map from VINT is disabled.
The spatial step (m) used by the fast-marching algorithm when solving the eikonal equation to compute traveltimes through the velocity model. The default is 5 m. Smaller values give more accurate traveltimes but increase computation time. Use a step no larger than the dominant wavelength at the shallowest depths.
A table of depth-varying velocity constraints applied during the VRMS construction. Each row specifies a depth range with minimum and maximum allowed interval velocities. Use this table to prevent the output VRMS from being influenced by unrealistic velocity values in the input VINT model.
Container grouping parameters that define the spatial and offset sampling used for ray tracing and VRMS computation. Adjusting these parameters controls the trade-off between accuracy and computation time.
The lateral grid spacing (m) at which VRMS values are calculated in the inline and crossline directions. The default is 500 m. Reduce this for higher lateral resolution in the output VRMS model, noting that smaller values significantly increase processing time. This parameter is not visible in the standard interface.
The depth step (m) at which VRMS values are computed vertically. The default is 500 m. This parameter is not visible in the standard interface.
The minimum lateral distance (m) over which VRMS values are averaged. The default is 250 m. This defines the minimum spatial aperture used when interpolating the VRMS field to the output grid.
The maximum lateral distance (m) over which VRMS values are averaged. The default is 2500 m. Increasing the maximum aperture allows the module to fill gaps in sparse areas of the velocity model by drawing from more distant samples.
The inline and crossline grid spacing (m) used to position ray-tracing source points. The default is 50 m. A finer step produces a denser ray coverage and a more detailed VRMS field but increases computation time considerably.
The vertical spacing (m) used to position ray-tracing source points through depth. The default is 50 m. Reduce this for denser vertical ray coverage in the shallow section where velocity gradients are strongest.
The increment (m) between successive source-receiver offsets used when integrating the VRMS over the offset range. The default is 50 m. A smaller offset step gives a more accurate VRMS at the cost of additional ray-tracing computations.
Selects whether the module runs on the CPU or GPU. GPU execution can significantly accelerate the fast-marching ray tracing for large 3D velocity models.
Enables distributed processing across multiple compute nodes. Configure node addresses and resource allocation in the cluster settings.
The number of data units sent to each compute node in a single work package during distributed execution. Increase for large datasets to reduce communication overhead.
When enabled, restricts the number of CPU threads used on each distributed node. Use this to leave resources available for other processes running on shared hardware.
An optional text label appended to the job name when running in distributed mode. Use this to distinguish multiple simultaneous jobs in the cluster queue.
When enabled, allows the user to specify which CPU cores the module may use via the Affinity mask. Leave disabled to allow the operating system to schedule threads automatically.
The CPU core affinity mask. Active only when Set custom affinity is enabled. Specify as a bitmask or core list to pin execution to particular CPU cores.
The number of CPU threads used for local processing. Set to match the number of available physical cores for best performance.
When enabled, the module is bypassed during batch execution. Use this to temporarily disable the module without removing it from the processing flow.
The computed VRMS model in the time domain. This model is sampled at the specified Output sample rate and Output samples, and can be used directly for NMO correction, semblance-based velocity analysis seeding, or as input to a stereo-tomography or Dix-inversion module.