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<< Click to Display Table of Contents >> Navigation: Velocity > R-cre to Vrms |
R-cre to Vrms converts a Common Reflection Element (CRE) velocity model — expressed in terms of the CRE radius parameter R — into a conventional root-mean-square (Vrms) velocity field. The conversion is performed by inverting the CRE moveout equation for Vrms at each time-trace grid point, using a least-squares approach controlled by a regularisation inversion factor. The resulting Vrms volume can be used directly as input to NMO correction, stacking, or depth conversion modules.
This module is typically placed after a CRE velocity analysis module in workflows that use the CRE operator for velocity picking, when the downstream processing chain requires a standard Vrms representation rather than the CRE R-parameter format.
The CRE velocity model gather (R-parameter field) to be converted. Connect from the output of a CRE-based velocity analysis module.
Velocity picking parameter set defining the output Vrms grid geometry (time axis sampling, trace spacing). Connect the same velocity picking params item used in the upstream velocity analysis module.
Near-surface reference velocity (m/s) used as the initial velocity at time zero in the CRE-to-Vrms inversion. Default: 1500 m/s. Set this to match the average velocity of the near-surface layer, typically from uphole or refraction data.
Lower bound (m/s) on the output Vrms field. Default: 1500 m/s. Vrms values computed below this threshold are clipped to the minimum. Set to a physically plausible water or near-surface velocity to prevent unphysical low-velocity artefacts.
Upper bound (m/s) on the output Vrms field. Default: 5000 m/s. Vrms values above this threshold are clipped. Set to a value representative of the maximum expected formation velocity in your survey area.
Start of the time range (s) over which the CRE-to-Vrms conversion is performed. Default: 0.1 s. Set to the shallowest time of interest in the survey.
End of the time range (s) for the conversion. Default: 5 s. Set to the maximum two-way time of interest.
Minimum CRE radius value (m) below which the conversion is considered unreliable and the output is set to the background velocity. Default: 60 m. Increase this threshold on data where the CRE picking is noisy or the reflector curvature is poorly constrained.
Regularisation weight (0–1) for the least-squares inversion used to convert R to Vrms. Default: 0.99. Values close to 1 produce a smooth, well-conditioned output closely following the background velocity trend; lower values give a solution more tightly fitting the CRE picks but potentially noisier.
Trace decimation step used when searching for the nearest CRE data point during the conversion. Default: 1 trace (no decimation). Increase to speed up processing when the CRE velocity field is densely sampled and the search can safely be coarsened.
Selects the processing device. CPU is adequate for this conversion module.
Configuration for distributed (cluster) execution.
Minimum number of gathers sent per work chunk during distributed execution.
When enabled, restricts CPU thread count per cluster node to the value in Number of threads.
Optional text appended to the distributed job name.
When enabled, applies the CPU affinity mask specified in Affinity.
CPU affinity mask applied when Set custom affinity is enabled.
Maximum number of CPU threads used during execution.
When enabled, this module is bypassed and data passes through unchanged.
The output Vrms velocity field converted from the input CRE R-parameter model. Connect to downstream NMO correction, velocity conversion, or depth migration modules that require a Vrms input.