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Weathering/drift statics computes static corrections that account for the effect of a near-surface low-velocity weathering layer, as well as instrument drift variations. For each location in the trace headers, the module reads the interval velocity model and calculates the two-way travel time through the zone between the recording datum and a user-defined pseudo-datum level, replacing the true velocity with the specified weathering velocity. The difference between the true travel time and the replacement travel time gives the correction that must be applied to remove the weathering effect. This approach is suitable for surveys where a depth-domain interval velocity model is available and the near-surface can be described by a single replacement velocity.
After computing per-trace correction values, the module interpolates them onto a regular 2D map using either Kriging or ABOS spatial interpolation, then assigns the gridded value to every source and receiver location from the trace headers. The resulting static correction item can be passed to a subsequent Apply statics module. A QC display of the drift statics map, the topography line, and the pseudo-datum line is available directly in the module interface.
The survey trace header table containing source and receiver coordinates with elevations. The module reads the XY positions and elevation values of all sources and receivers from this item to spatially assign the computed correction values. Connect from the geometry or preceding header module in the sequence.
Depth-domain interval velocity model displayed as a velocity-depth gather. This model defines the true near-surface velocity distribution used to compute the weathering correction. Typically produced by a depth velocity analysis or depth conversion module. The module displays the velocity model alongside the topography and pseudo-datum lines in the Graphics view.
The replacement velocity (m/s) used to substitute the true near-surface velocity when computing the static correction. Default: 2000 m/s. Minimum: 1 m/s. Set this to the average velocity of the weathering layer for your survey area. The module computes the one-way time through the near-surface zone using the true model velocity and compares it with the one-way time using this replacement velocity; the difference is the drift correction. Using a value close to the base of the weathering layer velocity minimises residual anomalies.
Defines how the lower boundary of the weathering correction zone (pseudo-datum) is determined. Default: Floating. Options: Constant — uses a fixed elevation for the pseudo-datum across the entire survey, specified by the Pseudo datum parameter; Floating — the pseudo-datum is placed at a fixed depth below surface elevation, so it follows the topography; Bins — the pseudo-datum level is taken from an external set of bin points with new elevations (requires the Input bins with new elevations connection). Use Floating for surveys with moderate topography relief, Constant for flat terrain, and Bins when you have an externally defined base of weathering surface.
The pseudo-datum value (m). Default: 200 m. When Pseudo datum type is set to Constant, this is the absolute elevation of the pseudo-datum plane. When set to Floating, this is the depth below surface at which the pseudo-datum sits (i.e., pseudo-datum elevation = surface elevation minus this value). Not used when Pseudo datum type is Bins.
Grid cell size in the X (inline) direction (m) used when interpolating the per-trace drift correction values onto the 2D output map. Default: 50 m. Minimum: 0.1 m. Smaller values produce a finer-resolution output map but increase computation time. Set to roughly the source or receiver line spacing for adequate spatial coverage.
Grid cell size in the Y (crossline) direction (m) for the output map. Default: 50 m. Minimum: 0.1 m. Use together with Map step X to control output map resolution. For 2D surveys, set this equal to Map step X or the nominal shot spacing.
Extra margin (m) added around the survey bounding box when creating the output drift statics map. Default: 100 m. Minimum: 0.1 m. The margin ensures that sources and receivers near the survey edge are fully covered by the interpolated map. Increase this value if peripheral traces show extrapolation artefacts.
The spatial interpolation algorithm used to create the continuous drift statics map from the discrete per-trace correction values. Default: Kriging. Options: Kriging — geostatistical interpolation that accounts for spatial correlation structure and provides smooth results with explicit variance control; Abos — a fast adaptive interpolation method that is computationally lighter than Kriging and works well on regularly sampled data. Kriging parameters (covariance type, range, number of points) are only available when Kriging is selected.
The variogram model used for Kriging interpolation. Default: Exponential. Options: Exponential, Spherical, Gaussian. The Exponential model suits data with gradual spatial correlation decay. The Spherical model has a finite range of influence and is appropriate for corrections with clear lateral spatial extent. The Gaussian model produces the smoothest interpolation and is suitable when corrections vary continuously without abrupt changes. Active only when Interpolation method is Kriging.
The range parameter (m) of the variogram model — the distance beyond which data points have negligible influence on the interpolated value. Default: 100000 m. Set to a value consistent with the spatial wavelength of the near-surface weathering variation in your survey area. A larger range results in smoother interpolation that honours long-wavelength trends; a smaller range gives more localised correction detail. Active only when Interpolation method is Kriging.
The maximum number of nearest data points used to estimate each grid node during Kriging interpolation. Default: 15. Higher values increase accuracy at the cost of longer computation. For dense surveys, values of 10–20 are typical. Active only when Interpolation method is Kriging.