|
<< Click to Display Table of Contents >> Navigation: Geometry > Redatum |
Redatum shifts seismic traces in time to correct for surface elevation differences, effectively moving the recording datum from the actual irregular acquisition surface to a flat reference level. This operation corrects for topographic variations between shot and receiver positions so that subsequent processing steps (stacking, migration, inversion) assume a uniform flat datum rather than the irregular field surface.
The module computes a time shift for each source and receiver location based on the elevation difference between the acquisition surface and the target datum. The shift can be calculated either using a constant near-surface velocity (V0) or a depth-dependent velocity model, which is more accurate in areas with complex near-surface geology. An 8-point sinc interpolation kernel is applied to the trace samples to achieve sub-sample accuracy when shifting. The corrected traces are written to a new output file, and source, receiver, and bin elevation values in the trace headers are updated to match the new datum.
Connect the seismic dataset to be datum-corrected. This handle provides access to the raw trace amplitude data and defines the sample interval used to convert time shifts into sample offsets.
Connect the trace header collection associated with the input dataset. The headers supply the source and receiver positions (X, Y) and their field elevations (Z), which are used to build the topographic surface and compute the required datum corrections. All traces must have valid source, receiver, and bin geometry assigned before running this module.
Specify the path and file name for the datum-corrected output dataset. The result is saved in GSD format. If the file already exists, behaviour is controlled by the Rewrite file and Saving mode settings below.
Controls how traces are written to the output file when the file already exists. Append adds the new traces after any existing content, which is useful when processing data in multiple passes. Direct overwrites the file from the beginning. Default: Append.
When enabled, any existing file at the output path is deleted and recreated from scratch before processing begins. Enable this option when you want a clean run without accumulating results from previous executions. Default: off.
Selects the method used to convert elevation differences into two-way travel-time shifts. Two options are available:
V0 — uses a single constant near-surface velocity for all locations. This is suitable for flat terrain or when a reliable velocity model is not available. The time shift is computed as the elevation difference divided by V0.
Depth velocity model — integrates interval velocities from a depth-velocity model along the vertical path between the acquisition surface and the target datum at each source and receiver location. This option produces more accurate corrections in areas with significant lateral near-surface velocity variation. When selected, a depth velocity gather must be connected and the Take elevations from parameter becomes available.
Default: V0.
The constant near-surface velocity (m/s) used to convert elevation differences to two-way travel-time shifts when Redatum by is set to V0. Set this to the representative velocity of the uppermost layer at the survey site — typically the near-surface weathering or soil velocity. Using a value that is too high will under-correct the datum shift; too low will over-correct it. Default: 1500 m/s. Valid range: 10–100000 m/s.
The number of traces loaded into memory and processed at one time. Larger values can improve throughput on fast storage but require more RAM. Reduce this value if the module runs out of memory on very large datasets. Default: 1000 traces. Minimum: 1.
These parameters control the grid used to build the interpolated topographic surface from the source and receiver elevation data. The module uses kriging to interpolate a smooth elevation map, then samples this map at each source and receiver location to obtain the target datum elevation for that point. Finer grid steps produce a more detailed surface but increase memory and computation time.
The grid spacing (m) along the inline direction for the interpolated topographic map. Set this value to approximately the average inline station spacing in your survey to capture the true topographic variation without unnecessary oversampling. Default: 50 m. Minimum: 1 m.
The grid spacing (m) along the crossline direction for the interpolated topographic map. For 2D surveys, this parameter has minimal effect. For 3D surveys, set it to approximately the average crossline receiver spacing. Default: 50 m. Minimum: 1 m.