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The Shift Data module applies a vertical time (or depth) shift to every trace in a seismic gather, moving the data to a common reference level. The module supports multiple shift methods: shifting to a fixed datum elevation, applying a constant time shift, moving to a floating datum derived from trace headers, shifting to the topographic surface, shifting by a value read from a selected trace header field, shifting by a mathematical expression involving header fields, or shifting according to an externally supplied elevation map (matrix). The near-surface interval created or removed by the shift is filled with a user-defined constant value.
Use this module whenever seismic data must be re-datumed before NMO correction, migration, or stacking — for example to apply floating datum statics, to remove topographic time shifts from land data, or to move marine data to a consistent water-bottom datum. The module works on time-domain, depth-domain, and frequency-domain gathers; the correct parameter set (time length, constant shift, or output length) is automatically exposed depending on the domain of the connected input gather.
Selects the method used to calculate the vertical shift for each trace. Available options:
To Datum — shifts all traces so that time (or depth) zero corresponds to the elevation specified in the Datum parameter. The shift is computed using source and receiver elevations from trace headers and the replacement velocity.
Const Shift — applies the same constant value (set in Constant manual shift) to every trace in the gather. Use this for a uniform bulk shift.
To Floating Datum — shifts each trace based on the floating datum elevation stored in the BIN_ELEV trace header (note: in g-Platform, BIN_ELEV contains the floating datum, while the actual surface elevations are in RECEIVER_ELEV and SOURCE_ELEV).
To Topography — shifts each trace to the actual surface elevation, read from the RECEIVER_ELEV and SOURCE_ELEV trace headers (the average of source and receiver elevation). Use this option to align data to the land surface for display or topographic muting.
By header — shifts each trace by the value read from the trace header field selected in the Shift by header parameter. Useful for applying static correction values already stored in headers.
By expression — computes the shift for each trace from a mathematical expression that may reference multiple trace headers. Example: SOURCE_STATIC + RECEIVER_STATIC combines source and receiver static corrections.
To matrix elevations — shifts each trace to an elevation level defined by the externally supplied elevation map connected to the Matrix with new topography input. This option requires the replacement velocity to convert the elevation difference to a time shift.
Default: To Datum.
When enabled, the datum elevation used for the shift calculation is taken from the Datum parameter instead of from the trace headers. When disabled, the module reads the datum directly from trace header fields. This option is only applicable for shift types other than To Datum (for which the manual datum is always used). Enable this option when your trace headers do not contain valid datum values.
Default: Disabled.
The target datum elevation in metres. All traces will be shifted so that time (or depth) zero corresponds to this elevation level. This parameter is active when Shift data type is set to To Datum, or when Use manual datum is enabled for other shift types. Set this to the same datum elevation that was used during geometry application and statics computation.
Controls how trace sample values are interpolated when the computed shift is a non-integer number of samples. Three options are available: 8 point interpolation uses eight surrounding samples and provides the best amplitude fidelity; Sinc uses a sinc kernel with configurable aperture; Linear is the fastest option but may introduce minor amplitude smoothing. Use 8-point interpolation for production processing and linear interpolation only for rapid QC.
Default: 8 point interpolation.
The fixed shift value applied to all traces when Shift data type is set to Const Shift. The unit (ms for time-domain data, m for depth-domain data) is determined automatically by the domain of the connected gather. A positive value moves data to later times (deeper); a negative value moves data to earlier times (shallower).
The amplitude value used to fill the empty samples that are created when traces are shifted. When data is shifted downward (later times), the earliest samples of the trace become empty; when shifted upward they are filled from this end. Set this to 0 (zero-fill) for most applications, which prevents spurious energy from appearing in the muted zone.
The replacement (near-surface) velocity in m/s, used to convert an elevation difference between the topographic surface and the datum into a two-way travel-time shift. This parameter is used for all shift types that involve an elevation-to-time conversion (To Datum, To Topography, To Floating Datum, To matrix elevations). Set this to the near-surface velocity appropriate to your survey: typically 1500 m/s for marine data and 1800–2500 m/s for land data depending on weathering conditions.
Default: 1500 m/s.
The desired length of the output trace in the domain of the input gather (ms for time, m for depth, Hz for frequency). When set to a negative value (default), the output trace length is kept identical to the input trace length. Set this to a positive value if you want to crop or extend the record length of the shifted data — for example, to shorten time-domain gathers after applying a downward datum shift so that the total output record length remains consistent.
Default: -1 ms (keep original length).