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<< Click to Display Table of Contents >> Navigation: Diffraction > Azimuth Selection Visualization |
Azimuth Selection Visualization computes and displays azimuth-sectored fold maps for a 3D seismic survey. For each defined azimuth sector, the module counts how many source-receiver pairs fall within the specified aperture radius around each bin and contribute to that azimuth range. The result is a 2D fold map — one per azimuth sector — that can be reviewed interactively using the mouse scroll wheel to cycle through azimuth sectors.
Use this module to diagnose azimuthal coverage and illumination uniformity in 3D surveys before applying azimuth-dependent processing such as anisotropy analysis or azimuth-sectored migration. The module is a visualization and QC tool and does not alter or output seismic trace data. A custom action, Calc bin aperture, is available to extract and export the aperture gather for a single selected bin to a SEG-Y file for detailed inspection.
Note: This module is deprecated. It may be retained for legacy project compatibility but is no longer actively developed.
The full set of trace geometry headers for the seismic dataset. These headers provide source and receiver coordinate information that the module uses to compute the azimuth and distance of each source-receiver pair relative to each bin center. This input must be connected to the geometry trace header collection for the survey being analyzed.
A spatially sorted index of the seismic trace headers. The module uses this sorted index to efficiently retrieve all traces whose midpoints fall within the aperture rectangle around each bin, avoiding a full scan of the entire dataset for every bin location. This input must be the sorted header index associated with the same dataset connected to the geometry input.
The bin grid definition for the 3D survey, which specifies the inline and crossline geometry, bin spacing, and coordinate reference. The module iterates over every bin in this grid (within the optional calculation area limits) to compute the fold map. The bin grid must match the survey area described by the trace geometry headers.
The index of the azimuth sector currently displayed in the fold map visualization. The total number of sectors is determined automatically from the First Azimuth, Last Azimuth, and Half Step Azimuth parameters. You can change this value interactively by scrolling the mouse wheel over the fold map display — the map updates in real time to show the fold for the selected sector. Valid range is 0 to (number of sectors minus 1).
The start of the azimuth range to analyze, in degrees. The module will generate azimuth sectors beginning at this angle and stepping toward the Last Azimuth value. Default is 10 degrees. Set this to the smallest azimuth direction of interest in your survey analysis. Azimuths are measured in degrees from North (or the survey reference direction).
The end of the azimuth range to analyze, in degrees. The module generates azimuth sectors up to and including this angle. Default is 170 degrees. Together with First Azimuth and Half Step Azimuth, this defines the total number of sectors: sectors = (LastAzimuth - FirstAzimuth) / (2 x HalfStepAzimuth) + 1.
An angular threshold in degrees used to handle near-zero-offset traces when computing azimuth. Source-receiver pairs whose angular separation (the angle between the source-to-image and receiver-to-image vectors) is smaller than this value are treated as effectively zero offset and included in the fold count regardless of their source-receiver azimuth. Default is 2 degrees. Increase this value if near-offset traces are being incorrectly excluded from azimuth sectors due to their ambiguous azimuth direction.
Half the angular width of each azimuth sector, in degrees. Each sector spans a total angular range of 2 x HalfStepAzimuth degrees centered on its nominal azimuth direction. Default is 10 degrees, giving a sector width of 20 degrees. Use smaller values for finer azimuth discrimination (more sectors, narrower bins), or larger values when the dataset has sparse azimuth coverage and sectors need to be wider to accumulate sufficient fold.
The maximum radial distance in meters from a bin center within which source and receiver locations are considered as contributors to the fold of that bin. Default is 1000 m. This controls the size of the circular search area centered on each bin. Larger apertures include more traces and produce smoother fold maps, but may blur the spatial resolution of azimuthal coverage variations. Set this to match the migration aperture you intend to use during processing.
The cross-azimuth aperture width in meters. This controls the lateral extent perpendicular to the azimuth direction over which source-receiver pairs are accepted into a given azimuth sector. Narrowing this value restricts the sector acceptance zone more tightly along the azimuth direction, while wider values allow more oblique traces to contribute. Leave at its default (unset) to use the same value as the main Aperture parameter.
The path and filename for the SEG-Y output file produced by the Calc bin aperture custom action. When you run that action, the traces from the aperture gather of the selected bin and azimuth sector are written to this file. Specify a full file path with a .sgy extension. This field is only used by the Calc bin aperture action and does not affect the main fold map computation.
A group of four parameters that restrict fold map computation to a rectangular sub-area of the survey, defined by inline and crossline number ranges. Use these limits to focus computation on the area of interest and reduce processing time on large surveys. Set any value to -1 to indicate no limit in that direction.
The first inline number to include in the fold map computation. Set to -1 (default) to start from the first inline of the bin grid with no restriction. Use a specific inline number to exclude inlines before that position from the computation.
The last inline number to include in the fold map computation. Set to -1 (default) to extend to the last inline of the bin grid with no restriction. Use a specific inline number to exclude inlines beyond that position.
The first crossline number to include in the fold map computation. Set to -1 (default) to start from the first crossline of the bin grid. Use a specific crossline number to restrict the computation area from the crossline direction.
The last crossline number to include in the fold map computation. Set to -1 (default) to extend to the last crossline of the bin grid. Use a specific crossline number to limit the computation area in the crossline direction.
A group of two parameters that specify which single bin to analyze with the Calc bin aperture action. Set the Inline and Crossline values to the bin coordinates of interest before running that action.
The inline number of the bin for which the aperture gather will be extracted and exported when the Calc bin aperture action is executed. Default is 0. Set this to the inline number of the bin you wish to inspect in detail.
The crossline number of the bin for which the aperture gather will be extracted and exported when the Calc bin aperture action is executed. Default is 0. Set this to the crossline number of the bin you wish to inspect in detail.
A group of parameters that optionally enforce minimum and maximum fold thresholds when building azimuth sector fold maps. Enable this group to exclude bins with fold counts outside an acceptable range, which can be useful for suppressing poorly sampled edge bins or highlighting over-sampled areas.
When enabled, the fold map computation enforces the Min Fold and Max Fold limits, and only source-receiver pairs whose bin fold count falls within these bounds are included. Default is off (no fold restriction applied). Enable this when you want to highlight only bins with statistically meaningful azimuth coverage.
The maximum allowed fold count per bin when Use Fold Limitation is enabled. Bins whose contributing trace count exceeds this value will be clamped or excluded from the map. Default is 1,000,000 (effectively no upper limit in most surveys). Reduce this value to identify and exclude anomalously high-fold areas such as over-sampled acquisition patches.
The minimum required fold count per bin when Use Fold Limitation is enabled. Bins with fewer contributing source-receiver pairs than this value will be excluded from the fold map display. Default is 5. Increase this value to hide under-sampled edge bins and focus the map on areas with reliable azimuth coverage.