Header and Trace Interpolation
Like all Insight workflow processes, it operates on the 2D records of its input volume. That input can be one of the following types of volume: shot records; common-channel records; image gathers; common offset inline or crossline records; 3D stack inline or crossline records; or land 2D records. Because the process operates on each record independently, you'll be manipulating the secondary domain of the record.
Missing items to add, remove or fill
|common offset inlines
|common offset crosslines
|3D stack inlines
|3D stack crosslines
|2D stack records
|land 2D shot records
|land 3D receiver-station records
Note: For marine data this process must also be used to remove the interpolated traces when you're finished with them, as it will reinstate the correct geometry headers. Do not simply use Trace Chooser!
- In the Control Panel, open the Process tab.
- At the tab header, click the Add icon and select New Process.
- Scroll down and double-click on Header and Trace Interpolation.
- Type a name for the process and click OK.
- Volume: A volume of shot, common-channel, image gather, inline or crossline records. If you're interpolating pre-regularisation data (i.e. shot or channel records), then the input volume must have station-based geometry.
- Output Sequence Mode: This applies when adding or removing channels (i.e. operating on shot records), offsets (i.e. operating on image gathers), crosslines (i.e. operating on common offset or 3D stack inlines) or inlines (i.e. operating on common offset or 3D stack crosslines). The output sequence can be fixed - meaning all output lines will have the same sequences; or relative - meaning the output sequence for each line is based on the input sequence and the new increment/traces added before/traces added after.
- Example Input Sequence: Describes the domain in which the process will act. When adding or removing shots (i.e. operating on common-channel records), this will show only a single example shot sequence, because of course each sail line has a different set of shots. Example - as it may vary between lines.
- Output Increment: The desired output trace locations in fixed sequence mode. This sequence can be the same as the input (to just fill holes); have a smaller increment (to interpolate new channels, offsets, inlines or crosslines); or have a larger increment (to drop the previously-interpolated traces). Extending the start and/or end values will result in extrapolation, if the "Extrapolate" option is
- Edge Action: Enable extrapolation or trimming of traces at the edges of the record. If not extrapolating, only internal holes smaller than the maximum hole size will be filled. This option is not available when interpolating inlines or crosslines.
Traces to add/trim at start/end: Number of traces to add or remove (depending on Edge Action) at the beginning and end of each line. Applies only when adding shots (i.e. operating on common-channel records), inlines or crosslines (i.e. operating on common-offset records), or using relative output sequences. Note when adding traces, the new traces must end on an extrapolated version of the input sequence.
- These numbers are in the new sequence increment.
- This is suitable for small numbers of traces; it's not intended for long-distance extrapolation.
- Max hole size to fill: Fill gaps between live traces up to this size (measured in # of traces). Holes larger than this will be left empty.
Of course if you're not adding traces to the output sequence, and there are no holes in your data, then the interpolation mode will have no effect.
- Headers Only: Any new traces are given interpolated headers, but the samples are left empty.
- Nearest: A copy of the nearest trace.
- Lagrangian: Generates a smooth function from the values of the nearest four traces (two on each side). When there are insufficient nearby traces (e.g. at the edge of the volume or a too-large hole), this mode will fall-back to linear and then nearest. Extrapolation uses the nearest trace.
- DUG Reg 2D: Interpolation utilising a constrained inversion based on the minimum-weighted norm algorithm of Liu and Sacchi (2004). Operates only on TWT data with an integral-millisecond sample interval. Note: DUG Reg 2D will interpolate missing traces on the output grid, even when decimating the trace spacing. Please use Headers Only mode if just dropping traces.
- Spatial half-window (traces): number of input traces in the spatial half window. Large windows are required for extensive extrapolation.
- Temporal half-window (ms): length of the temporal half-window.
- Dip limit (ms / trace): limit on the dips to consider for interpolation based on input trace spacing.
All headers are used to interpolate values for new traces, as described below in Headers Set.
One special value of the TRID header has a specific meaning: traces with TRID=30000 are considered to be marked dead. This means that they will be treated as missing for the purpose of interpolating samples only. That is, new samples will be interpolated for this trace, but not new headers.
The headers of existing input traces are unmodified, with two exceptions: when interpolating pre-regularisation data (i.e. shot/channel volumes), the CDP Index (HCS) and Receiver-Station Index (GAPS) headers may be updated to accommodate the new trace geometry.
On newly-created traces, some headers are set according to specific rules:
- EP, TRACR, CDP, HCS, CDPT, GAPS: DUG geometry headers are calculated according to the usual station-based rules
- CDPX, CDPY: Calculated from the interpolated SX, SY, GX, GY except when interpolating offsets, inlines or crosslines; from the survey for 3D volumes
- OFFSET: Calculated from the interpolated SX, SY, GX, GY except when interpolating offsets, inlines or crosslines
- OTRAV (Azimuth): Calculated from the interpolated SX, SY, GX, GY except when interpolating offsets, inline or crosslines (where reciprocal traces are assumed to have the same azimuth)
- SX, SY, GX, GY: Calculated from the interpolated CDPX, CDPY, OFFSET, OTRAV (Azimuth) when interpolating offsets, inlines or crosslines
- YEAR, DAY, HOUR, MINUTE, SEC: Are interpolated as a group, so that the resulting time is correct
- TRID: Interpolated traces are set to 30001; extrapolated traces to 30002
All other trace header values are linearly interpolated from the two neighbouring live traces. Or when extrapolating, copied from the nearest live trace.