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<< Click to Display Table of Contents >> Navigation: AVO > Depth angles creation procedure |
Note: This module is deprecated and is retained for legacy workflow compatibility only. It may be removed in a future release.
The Depth angles creation procedure computes per-sample, per-trace reflection angles for pre-stack depth-domain gathers. For each output bin, the module uses a pre-computed travel-time table (the depth time table input) together with a depth interval velocity model to derive the angle at which each ray segment arrives at depth. The result is a depth-domain angle gather written to the specified output file.
The algorithm works sample by sample in depth. At each depth sample it looks up the one-way travel times from source and receiver to that depth point (obtained from the time table), computes the time difference between adjacent depth levels, and then applies the relationship:
angle = arccos( V_avg * dT / dZ )
where V_avg is the average interval velocity between adjacent depth samples (m/s), dT is the one-way travel-time change over the depth step (s), and dZ is the depth step size (m). The half-opening angle at the reflector is computed separately for source and receiver ray legs, then summed to give the full opening angle for each trace. Two azimuthal directions (inline and crossline) are evaluated independently; whichever direction yields a valid result is stored in the output.
A key validation requirement is that the input seismic data, the time table, and the depth velocity model must all share a common, constant datum elevation. If the datum values differ between sources and receivers, or between the data and the velocity model, the module will stop with an error. The source and receiver datum must be identical for every trace in the input.
This module belongs to the AVO processing group. It is intended as a preparatory step before angle-domain AVO analysis or angle-dependent stacking in the depth domain.
Connect this item to the pre-stack depth-migrated (PSDM) seismic data file that you want to convert to angle gathers. This is the primary seismic dataset: the module reads its sample values to determine the geometry (number of samples, sample interval, offset, datum) for every trace. The data must have a constant datum for all source and receiver positions — any datum inconsistency will cause the module to report an error before processing begins.
Connect this item to the trace header vector corresponding to the seismic data connected above. The trace headers supply the bin assignments, source and receiver positions, offsets, and datum elevations for each trace. These headers are used to group traces by bin and to determine the source-receiver geometry needed for angle computation. The trace header geometry must be fully defined and consistent with the SEG-Y data file.
Connect this item to the pre-computed travel-time table (TTT) file in SEG-Y format. The time table stores the one-way travel times from each surface source or receiver position to every depth point across the model grid, computed by a wave-equation or ray-tracing solver (such as the Eikonal fast-marching method). These travel times are the core input for the angle calculation: the module looks up the time at two adjacent depth levels for both source and receiver positions to derive the ray slowness direction at each depth sample.
Connect this item to the trace header vector corresponding to the time table SEG-Y file. The time table headers define the spatial coordinates (inline picket and crossline picket) of each source position for which a travel-time trace was computed. The module uses these coordinates to construct the 2D spatial grid of the time table and to interpolate travel times at the precise source and receiver positions for each seismic trace. The datum recorded in the time table headers must match the datum of the seismic data.
Connect this item to the bin point vector that defines the survey geometry — the set of output bin positions and their associated coordinate transformation parameters (origin, inline azimuth, and crossline azimuth). The module uses the first bin in this vector to define a local coordinate system in which inline and crossline offset directions are computed independently for each trace. This geometry item is typically produced by the Binning or Calculate GridParams modules.
Connect this item to the depth-domain interval velocity model gather. The velocity model must be in the depth domain (depth axis in metres) and is organised as a gather of traces, one trace per spatial position. At each bin location the module finds the nearest velocity trace using a 2D spatial search, then reads the local interval velocity at each depth level. This velocity is used in the angle formula to convert travel-time gradients into ray angles. The velocity model must share the same datum as the seismic data and the time table.
Specify the full path and file name for the output angle gather, using the .gsd extension (g-Platform internal seismic data format). The output gather has the same trace layout and depth sampling as the input seismic data, but each sample value contains the computed opening angle (in radians) for that trace and depth level, rather than an amplitude. If the output file already exists, the module will prompt you to confirm overwriting before processing starts.
This module has no user-configurable processing parameters beyond the standard SEG-Y reading settings and execution settings described below. All processing is governed entirely by the input data items connected above.
This group contains standard SEG-Y file reading parameters that control how the input seismic data file and the time table file are opened and cached during processing. These settings are shared between both SEG-Y inputs. The default values are suitable for the majority of datasets; change them only if you encounter performance issues or if your SEG-Y files use non-standard header layouts. Refer to the SegyReadParams common component documentation for a description of each sub-parameter.
Select the hardware on which the angle computation is performed. Choose CPU for standard multi-threaded processing on the workstation processor, or GPU if a compatible graphics card is available and the dataset is large enough to benefit from GPU acceleration.
Enable this option to distribute the processing across multiple compute nodes in a cluster environment. When enabled, the work is split into chunks that are submitted to remote nodes managed by the g-Platform distributed execution framework. This is recommended for very large 3D datasets where single-node processing would be prohibitively slow.
Sets the minimum number of bins processed in each distributed execution chunk. Larger values reduce the scheduling overhead per chunk but may lead to uneven load distribution if the dataset is small. The default value is appropriate for most surveys.
When distributing execution across cluster nodes, this setting caps the number of CPU threads used on each remote node. Use this to prevent the angle computation from monopolising an entire node when other jobs are running concurrently on the same machine.
An optional text label appended to the job name when submitting tasks to the distributed execution queue. Use this to distinguish between multiple concurrent runs of this module on the same cluster, for example when processing different survey areas in parallel.
Enable this option to manually control which CPU cores are used during processing. When enabled, the Affinity field below becomes active. Leave this disabled to let the operating system assign cores automatically.
Specifies the CPU core affinity mask when Set custom affinity is enabled. This is an advanced setting intended for performance tuning on NUMA (non-uniform memory access) systems. Leave at the default value unless you have a specific reason to pin the process to particular cores.
Sets the maximum number of parallel CPU threads used during processing. The module processes bins in parallel; increasing this value speeds up computation on workstations with many cores. The default is typically set to the number of logical processors available on the machine. Reduce this value if you need to leave processor capacity available for other tasks running simultaneously.
When enabled, this module is bypassed entirely during flow execution — the module is skipped without error and the flow proceeds to the next step. Use this option to temporarily disable angle creation in a processing flow without removing the module from the flow graph.
This module does not produce a data connector output. All results are written directly to the file specified in the Output file name input field. The output is a depth-domain angle gather in the g-Platform internal format (.gsd). It has the same trace count, bin assignments, and depth sampling as the input seismic data. Each sample stores the full opening angle (source-side plus receiver-side, in radians) at that depth level for the corresponding trace offset. Samples for which a valid travel time could not be retrieved from the time table are left as zero. After execution, load this file into g-Platform as an angle gather for subsequent AVO analysis or angle-dependent stacking.