Applying elevation/topography values to seismic trace headers
Topography or elevation profile is one of the key components of land seismic processing. When vintage onshore acquisition crews recorded source and receiver elevations in a spreadsheet rather than in SPS format, those elevation values are available as an ASCII file. The ApplyTopographyFromASCII module reads elevation data from a poststack horizon (loaded from such an ASCII file) and writes the interpolated elevation values into the source and/or receiver elevation fields of the seismic trace headers.
The module uses kriging-based spatial interpolation to estimate the elevation at every source and/or receiver location, even when the ASCII file contains only a sparse set of measured elevation points. The updated trace headers can then be used for subsequent static corrections or further processing steps.
Note: This module is marked as deprecated. For new projects, consider using the standard geometry elevation import tools available in g-Platform.
Trace headers input - this information is required to update the trace headers with the topography information. As we mentioned in the introduction, source and receiver headers needs to be updated with the elevation from the ASCII file. Connect/reference to the Output trace headers (which doesn't have elevation information in their trace headers).
Connect this input to the trace header dataset whose source and/or receiver elevation fields need to be populated. This is typically the output of a geometry assignment step where elevation values are missing or set to zero. The module will iterate over every source and receiver position stored in this header set and assign interpolated elevation values from the horizon.
PostStack Horizon - connect/reference to the output/post stack horizon. It takes the coordinate information from the horizon.
Connect this input to a poststack horizon that represents the topographic surface. The horizon is expected to have been imported from the ASCII elevation file and carries X, Y, and Z (elevation) coordinates at sampled points across the survey area. The module uses these points as the control data for interpolating elevation at all source and receiver positions. The denser and more evenly distributed these horizon points are, the more accurate the interpolated elevations will be.
Calculation type { S, R, SR } - specifies the type of calculation. Select the appropriate calculation type from the drop down menu. By default, SR(Source Receiver).
This parameter controls which station types receive updated elevation values from the topography data. Three options are available:
S — update the elevation of source positions only. Use this option when only source elevation data is available in the ASCII file, or when receiver elevations are already correctly assigned in the trace headers.
R — update the elevation of receiver positions only. Use this option when only receiver elevation data is available, or when source elevations are already correctly set.
SR (default) — update elevations for both source and receiver positions. This is the most common choice when a complete topographic surface has been digitized and both sets of elevations need to be assigned from scratch.
Interpolation - this section deals with interpolation of the elevation data. The elevation file consists of few source and/or receiver elevation information. To get the elevation for all the source/receivers, we need to interpolate the elevation data from the available information only.
The module uses a fast kriging algorithm to interpolate elevation values from the sparse set of measured points in the ASCII file to all source and receiver positions in the dataset. The two parameters below control how that interpolation is performed. Choosing appropriate values is important: too small a search radius will leave stations without an assigned elevation (counted as errors), while too large a radius may incorporate distant, geologically unrelated elevation data.
MaxDist - specify the maximum distance for the interpolation of topographic values
Sets the maximum search radius (in metres) within which the module looks for known elevation control points when computing the interpolated elevation at a source or receiver location. The default value is 50 m. If no horizon point falls within this distance of a given station, the module cannot assign an elevation to that station, and the station is counted as an error in the ErrorCount output. Increase this value if your survey has widely spaced elevation control points; decrease it if the topography changes rapidly over short distances and you want to avoid mixing elevation data from different terrain segments.
MaxPointCount - specify the number of interpolation points
Sets the maximum number of nearby horizon points used by the kriging interpolator to estimate the elevation at each station. The default value is 100. Using more points generally produces a smoother interpolation but increases computation time. If the horizon is very densely sampled, reducing this value can speed up processing without significantly affecting accuracy. If the horizon is sparse, set this value to a number equal to or less than the total number of horizon points available.
Skip - By default, FALSE(Unchecked). This option helps to bypass the module from the workflow.
When checked, this module is skipped entirely during workflow execution and the input trace headers are passed through unchanged. Use this option to temporarily disable elevation assignment — for example, to test how downstream processing behaves without updated elevations — without removing the module from the workflow.
Trace headers output - outputs the trace headers with updated elevation information. These trace headers can be used for further processing.
This output carries the full set of trace headers from the input, with source and/or receiver elevation fields updated according to the selected Calculation type. Connect this output to downstream modules that require elevation information — such as static correction calculation or geometry QC tools. Stations whose elevation could not be interpolated (because no horizon point was found within MaxDist) retain their original elevation value and are counted in the ErrorCount output.
ErrorCount - displays the error information if there are discrepancies in the input elevation file.
After execution, this field reports the number of source or receiver stations for which the module was unable to compute an interpolated elevation. A station fails to receive an elevation when no horizon point falls within the MaxDist search radius of that station's position. A value of zero indicates that elevations were successfully assigned to all stations. A non-zero value signals that the MaxDist parameter may need to be increased, or that the horizon data has gaps covering part of the survey area. Investigate stations with missing elevations before proceeding with static corrections.
There are no action items available for this module.
YouTube video lesson, click here to open [VIDEO IN PROCESS...]
Yilmaz. O., 1987, Seismic data processing: Society of Exploration Geophysicist
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