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<< Click to Display Table of Contents >> Navigation: Velocity > VRMS to stereo tomo parameters |
This module converts an input VRMS (root-mean-square velocity) model into a set of tomo parameters that can be used as input for stereo-tomography. Starting from the input VRMS field, the module constructs an initial interval velocity model through Dix inversion or a linear gradient, then packages the result together with ray-tracing geometry settings and solver configurations needed to drive a subsequent tomographic update.
Use this module when you have an VRMS velocity model — for example from semblance picking — and want to initialise a stereo-tomography workflow for depth velocity model building. The output tomo item is consumed by the Stereo-tomography engine module.
The input VRMS velocity model. This is typically the result of semblance-based velocity analysis or a converted stacking velocity field. The model provides the time-domain velocity information that this module inverts to build the initial depth model.
Container grouping all parameters used to define the geometry, velocity initialisation, and depth range for the tomo parameter set to be created.
A label assigned to the tomography line output. This name is used to identify the resulting tomo item in downstream processing modules.
The near-surface velocity (m/s) used as the starting point for the velocity inversion. The default value is 1500 m/s, which is appropriate for water-saturated sediments. For land surveys with hard surface conditions, increase this value to match the measured near-surface velocity.
The lateral grid spacing (m) used when searching for VRMS values along the X (inline) direction. The default is 250 m. Smaller values produce a denser sampling of the VRMS field and a more detailed initial model, but increase computation time.
The time step (s) used when sampling the VRMS model vertically. The default is 0.1 s. Reduce this value for higher vertical resolution in the constructed tomo parameters.
The maximum two-way time (s) to which the VRMS model is sampled. The default is 5 s. Set this to match the maximum reflector time of interest. This parameter is overridden when Detect maximum time is enabled.
The list of source-receiver offsets (m) at which synthetic ray pairs are generated for the tomo parameter set. Nine default offset values are provided. These offsets define the geometry of the virtual reflection events used in the tomographic inversion. Add or remove offsets to match the offset range of your actual data.
Individual offset value (m) within the offset collection. Each row in the list represents one target offset. Edit these values to span the near-to-far offset range of the seismic dataset.
Selects how the initial interval velocity model is constructed. Gradient uses a simple linear velocity increase with depth defined by the gradient range parameters. Dix applies the Dix inversion formula to convert the input VRMS field to interval velocities — this is recommended when the VRMS model is reliable and the geology is relatively simple.
The velocity (m/s) at the surface (depth = 0) when the gradient initialisation is selected. The default is 1500 m/s. This parameter is only active when Initial velocity type is set to Gradient.
The velocity (m/s) at the base of the model when gradient initialisation is selected. The default is 6000 m/s. Together with the surface velocity, this defines the linear velocity gradient applied throughout the model depth.
The vertical sample spacing (m) of the constructed depth velocity model. The default is 5 m. Use finer spacing when the velocity model contains rapid vertical changes at shallow depths.
The maximum depth (m) to which the output velocity model is constructed. The default is 10000 m. Set this to at least the depth of the deepest target horizon.
The reference datum elevation (m) used for the velocity model. The default is 0 m. This parameter is overridden when Detect datum is enabled in the Auto detect settings.
Container grouping options to automatically derive key model boundaries from the input data. When enabled, these settings replace the corresponding manually entered values.
When enabled (default: true), the module automatically determines the datum elevation from the input VRMS data, overriding the manually set Datum parameter.
When enabled (default: true), the module automatically determines the maximum two-way time from the input VRMS model, overriding the manually set Max time parameter.
When enabled (default: true), the module scans the input VRMS field to determine the minimum velocity and use it as the lower bound for the Dix inversion, rather than relying on the Min VRMS to consider value.
When enabled (default: true), the module scans the input VRMS field to determine the maximum velocity and uses it as the upper bound for the Dix inversion, rather than relying on the Max VRMS to consider value.
Container grouping parameters that control the quality filtering and solver behaviour when Initial velocity type is set to Dix.
When enabled, VRMS values that fall outside the acceptable range defined by Min VRMS to consider and Max VRMS to consider are excluded from the Dix inversion. This prevents physically unrealistic velocities from corrupting the initial model. Default is false.
The minimum acceptable VRMS value (m/s) when filtering out bad velocities. The default is 1500 m/s. Values below this threshold are treated as unreliable and skipped if Don't use bad Vrms values is enabled. This parameter is overridden if Detect minimum velocity is enabled.
The maximum acceptable VRMS value (m/s) when filtering out bad velocities. The default is 4500 m/s. Values above this threshold are treated as unreliable and skipped if Don't use bad Vrms values is enabled. This parameter is overridden if Detect maximum velocity is enabled.
Container grouping iteration and spatial step parameters for the Dix-inversion solver. These control convergence and the spatial resolution of the inverted interval velocity field.
The number of outer (global) solver iterations. The default is 2. Each global iteration updates the full velocity model. Increasing this value improves convergence but increases computation time.
The number of inner (local) solver iterations per global iteration. The default is 5. These iterations refine the solution locally within each global update step.
The convergence tolerance for the solver. The default is 1×10⁻⁶. The solver stops early when the residual drops below this threshold. Reduce this value only if higher precision is required.
The inline calculation step (m) used when solving the Dix inversion on the computational grid. The default is 200 m. A smaller step gives higher lateral resolution but increases compute time.
The crossline calculation step (m) used when solving the Dix inversion on the computational grid. The default is 200 m. Match this to the crossline bin spacing of the velocity model for best results.
A table of time-varying velocity constraints applied during the Dix inversion. Each row defines a time interval with a minimum and maximum allowed interval velocity. Use this table to impose geological velocity bounds and prevent the inversion from producing physically unrealistic results.
Individual velocity-time function picks that populate the interval velocity table. Each pick is defined by a start time, a minimum velocity, and a maximum velocity.
The two-way time (s) at which a velocity constraint interval begins. Enter the top of each geological interval for which you want to constrain the inversion.
The minimum allowed interval velocity (m/s) within the constraint interval starting at Time start. The Dix inversion will clamp any inverted velocity below this value up to this minimum.
The maximum allowed interval velocity (m/s) within the constraint interval starting at Time start. The Dix inversion will clamp any inverted velocity above this value down to this maximum.
When enabled (default: true), the module prevents the interval velocity from decreasing faster than allowed by the Fraction of decrease parameter. This stabilises the inversion by imposing a physical monotonicity constraint on the depth velocity profile.
Controls how strongly interval velocity decrease is suppressed when Limit decrease of VINT is enabled. A larger value permits less velocity decrease — set to a high value to enforce a monotonically increasing velocity profile. A smaller value allows gradual velocity inversions.
Container grouping advanced regularisation parameters for the Dix solver. These control the smoothness and stability of the inverted velocity field in the lateral (X) and vertical (Z) directions.
The lateral (X-direction) regularisation parameter. The default is 10. Higher values enforce greater lateral smoothness in the output interval velocity model. Increase this if the Dix inversion produces erratic lateral variations.
The vertical (Z-direction) regularisation parameter. The default is 10. Higher values enforce greater vertical smoothness. Increase this when the interval velocity function shows high-frequency oscillations with depth.
An advanced solver weighting parameter (default: 1.5) that controls the balance between the data fit and the regularisation terms in the inversion objective function. Use the default value unless the inversion shows instability.
An advanced solver step-size parameter (default: 1) that controls the update magnitude in each solver iteration. Reduce this value if the inversion diverges; increase it slightly to accelerate convergence for well-constrained problems.
Selects whether the module runs on the CPU or GPU. GPU execution can accelerate processing 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 complete tomography parameter set built from the input VRMS model. This item contains the ray-pair geometry, the initial interval velocity model, and all solver settings needed by the Stereo-tomography engine. Connect this output to the input of a stereo-tomography update module.
The initial depth-domain interval velocity model derived from the VRMS inversion (either Dix or gradient). This model can be displayed and quality-checked independently before being passed to the tomographic solver.