Description

The Tomo statics 2D/3D module derives near-surface static corrections by performing refraction tomographic inversion of first-break travel-time picks. The module builds a depth-domain near-surface velocity model by iteratively tracing rays from sources to receivers through the model and updating the velocity field to minimise the difference between modelled and observed first-break travel times. Static corrections are then computed by integrating the reciprocal of the inverted velocity model from the acquisition surface to the datum.

This module handles both 2D line and 3D areal surveys, and includes a velocity regularization option to constrain model smoothness. Use it when conventional refraction statics methods based on delay-time or plus-minus approaches produce insufficient results, particularly in areas with laterally varying or deeply weathered near-surface conditions.

Input data

3D case

Boolean flag. When enabled the module treats the dataset as a 3D survey and uses both inline and crossline geometry during inversion. Disable for 2D line-based processing.

Output velocity geometry

Enumeration selecting how the output velocity grid extents and sampling are determined. Options are: User defined (use the grid parameters specified manually in the Output geometry fields), By first-break picking (derive the grid extent automatically from the spatial extent of the imported picks), and By seismic data (derive extent from the connected seismic data headers).

Output geometry

Container defining the spatial extent and sampling of the output depth velocity grid when Output velocity geometry is set to User defined. Specify minimum, maximum, and step values in both X and Y to define the model coverage area.

Min picket X

Minimum inline coordinate of the output velocity grid when using User defined geometry.

Max picket X

Maximum inline coordinate of the output velocity grid.

step picket X

Inline sampling interval of the output velocity grid. Default: 25 m.

Min picket Y

Minimum crossline coordinate of the output velocity grid.

Max picket Y

Maximum crossline coordinate of the output velocity grid.

step picket Y

Crossline sampling interval of the output velocity grid. Default: 25 m.

Input trace headers

Link to the trace header vector containing source and receiver coordinates for all traces. These headers define the acquisition geometry used by the tomographic ray tracer.

Input SEG-Y data handle

Link to the SEG-Y file handle containing the raw seismic data used for first-break picking and for reading trace amplitudes during the inversion. Connect the same data set from which the first-break picks were made.

Parameters

Velocity model params

Container group controlling the parameterization and spatial extent of the near-surface velocity model built during tomographic inversion.

Deepest refractor velocity

Velocity (m/s) assigned to the deepest refractor in the initial model. Default: 6000 m/s. This serves as the starting velocity for the lowermost layer and constrains the inversion from producing velocities above this value.

Datum

Replacement datum elevation (m) to which static corrections are computed. Default: 1000 m. Set this to the project datum elevation consistent with your processing flow.

Max depth

Maximum depth (m) of the near-surface velocity model. Default: 1500 m. Set this to the base of the weathering zone or the maximum depth illuminated by the first-break picks.

Step Z depth out

Vertical sample interval (m) of the output near-surface velocity model. Default: 10 m.

Step X depth out

Inline spatial sampling (m) of the tomographic velocity model output. Default: 200 m.

Step Y depth out

Crossline spatial sampling (m) of the tomographic velocity model output. Default: 200 m.

Step X depth time table

Inline grid spacing (m) of the internal ray-tracing travel-time table. Default: 25 m. Finer spacing improves travel-time accuracy but increases memory usage.

Step Y depth time table

Crossline grid spacing (m) of the internal ray-tracing travel-time table. Default: 25 m.

Horizontal smooth

Radius (m) of horizontal smoothing applied to the velocity update at each iteration. Default: 200 m. A larger value produces a smoother model and is recommended in areas with sparse pick coverage.

Fresnel Width

Half-width (m) of the Fresnel zone used to weight ray contributions to the velocity tomographic update. Default: 10 m.

Frequency

Dominant frequency (Hz) of the first-break arrivals used to estimate the Fresnel zone radius. Default: 5 Hz. Set this to the characteristic frequency of the first-break wave train in the data.

Horizontal window for trend detection

Lateral window length (m) over which a background travel-time trend is estimated and removed from the picks prior to inversion. Default: 2000 m.

Vertical window for trend detection

Vertical window length (m) used for background trend estimation. Default: 100 m.

Number of global iteration

Number of outer inversion iterations in which the full velocity model is rebuilt and the complete ray set is re-traced. Default: 5. Monitor the residual travel-time misfit after each iteration to assess convergence.

Number of local iteration

Number of inner (local) iterations applied to a local model region before updating the global model. Default: 5.

Enable velocity inversion

When enabled, allows the velocity model to contain layers where velocity decreases with depth. Default: disabled. Enable only when a low-velocity zone is geologically expected.

Velocity min

Minimum permitted velocity (m/s) in the inverted near-surface model. Default: 1000 m/s.

Velocity max

Maximum permitted velocity (m/s) in the inverted near-surface model. Default: 7000 m/s.

Offset min

Minimum source-receiver offset (m) of first-break picks used in the inversion. Default: 0 m.

Offset max

Maximum source-receiver offset (m) of first-break picks used in the inversion. Default: 5000 m. Exclude picks at offsets beyond this value where the signal-to-noise ratio of the first breaks deteriorates.

Regression aperture

Lateral aperture (m) over which a local regression is applied to the near-surface velocity model to provide a smooth initial estimate for the iteration. Default: 300 m.

Maximum deviation (picking to model)

Maximum allowable difference (m) between the observed pick travel time and the value predicted by the current model. Picks with larger deviations are rejected as outliers. Default: 100 m. Reduce this value to make the outlier rejection more aggressive.

Residual solver

Container group with parameters controlling the optional residual statics computation applied after the tomographic velocity update.

Calculate residual statics

When enabled, the module computes residual static corrections after each global iteration to account for small anomalies not resolved by the tomographic velocity model.

Global iterations count

Number of global iterations in the residual statics solver. Default: 2.

Local iterations count

Number of local iterations in the residual statics solver. Default: 2.

Number of azimuthal direction

Number of azimuthal sectors used to stratify the data during the 3D inversion. Default: 1 (azimuth-independent). Increasing this value improves azimuthal coverage sampling for 3D surveys with wide-azimuth acquisition.

Velocity regularization params

Container group controlling spatial regularization applied to the velocity update to suppress oscillations and enforce model smoothness.

Use regularization

When enabled, applies Tikhonov-style regularization to the velocity update during each iteration. Regularization adds a penalty on velocity roughness, producing smoother models. Enable in areas with noisy or sparse picks to prevent overfitting.

Regularization weight X

Relative weight of the regularization penalty applied in the inline (X) direction. Default: 1. Larger values produce stronger smoothing in the inline direction.

Regularization weight Y

Relative weight of the regularization penalty in the crossline (Y) direction. Default: 1.

Regularization weight Z

Relative weight of the regularization penalty in the vertical (Z) direction. Default: 1. Increase this value to enforce stronger vertical smoothness when the model shows layering artefacts.

Number of iterations

Number of regularization sub-iterations applied at each global inversion step. Default: 2. More sub-iterations produce a smoother model update per step.

Window for calculating V0

Lateral search radius (m) used to estimate the initial near-surface velocity (V0) from neighboring picks before starting the tomographic iterations. Default: 100 m.

Horizontal smooth distance V0

Lateral smoothing distance (m) applied to the initial V0 velocity field before commencing the iterative tomographic updates. Default: 3000 m. A large value provides a smooth, low-frequency starting model that helps convergence toward the global minimum.

Custom actions

Solve

Launches the tomographic inversion using the currently loaded first-break picks. The module runs all global and local iterations and outputs the near-surface velocity model and static correction field.

Import FBPicking

Imports first-break pick times from an external file into the module for use during inversion. Use this to load picks made outside of g-Platform or from a previous picking session.

Calculate V0 matrix

Computes the initial near-surface velocity (V0) spatial distribution from the imported first-break picks without running the full iterative inversion. Use this to preview the starting model before committing to the full solve.