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The Geometry chapter groups all modules responsible for assigning, loading, verifying, and manipulating acquisition geometry information stored in seismic trace headers. Correct geometry is the foundation of every subsequent processing step: accurate offset, azimuth, midpoint, and coordinate values in the trace headers are required for binning, stacking, velocity analysis, static corrections, and imaging. Without properly assigned geometry, seismic data cannot be meaningfully sorted, corrected, or migrated.
Geometry workflows in g-Platform typically proceed in stages. First, acquisition geometry is loaded from external files (SPS, SEG-P, UKOOA P1/90, ASCII observe logs, or offset tables) and merged with raw seismic data to populate shot, receiver, midpoint, and offset header fields. Next, the assigned geometry is verified using QC tools that check header consistency, fold distribution, azimuthal coverage, and first-break alignment. Finally, specialized modules handle marine-specific tasks such as streamer feathering correction and nominal geometry generation, coordinate system transformations, topography assignment, and grid parameter calculations needed before binning and migration.
The chapter is organized around the following functional groups:
These modules read geometry information from standard industry file formats and write the coordinates, offsets, and station numbers into trace headers. Load geometry from SPS reads the widely-used Shell Processing Support format containing shot and receiver point definitions. Load geometry from SEG-P and Load geometry from UKOOA P1/90 support standard marine and land geometry formats used by regulatory bodies and contractors. Load geometry from ASCII and Load observe log from ASCII handle project-specific text formats. Once geometry is loaded, Geometry application merges the geometry database with the raw seismic traces to populate all required header fields. Apply offsets file to geometry allows corrections to be applied from a pre-computed offsets table, useful when receiver positions need to be adjusted after initial loading. SPS to trace collection and Trace headers to SPS files convert between SPS format and the internal g-Platform trace collection format, facilitating data exchange with external systems. UKOOA P1 import geometry provides an alternative UKOOA importer with additional format options.
Binning modules assign common midpoint (CMP) bin numbers to traces and define the processing grid. Binning 2D and Binning 2D EXT compute CMP locations for 2D land and marine surveys. Binning 2D By Line performs binning with the processing line geometry explicitly specified. Binning 3D handles 3D surveys by projecting midpoints onto a defined inline/crossline grid. RP Binning 3D performs reflection-point binning suitable for wide-azimuth and OBN datasets. Post-stack binning (2D) re-bins already stacked 2D data. Bingrid manipulation edits or transforms an existing bin grid definition. Calculate GridParams derives optimal inline and crossline spacing, azimuth, and origin from the data coordinates before binning is performed.
Coordinate systems conversion transforms shot and receiver coordinates between geographic (latitude/longitude) and projected (UTM, local grid) coordinate systems, ensuring consistent spatial referencing throughout the project. Set topography assigns surface elevation values to shot and receiver positions in the trace headers, which are required for computing datum static corrections. Update bins topography updates elevation data for bin centres after the processing grid has been defined. Redatum adjusts trace time references to a new datum level using velocity and elevation information, moving the effective recording surface up or down.
Marine-specific modules address the unique geometry challenges of towed streamer acquisition. Nominal marine geometry constructs idealised receiver positions for a streamer spread based on the vessel track, cable length, and group interval when actual feather positions are unavailable. Marine Geometry swap exchanges source and receiver geometry assignments, which is needed when acquiring data with multiple sources and cables in alternating fire patterns. Virtual geometry marine (2D) creates a regularised 2D marine geometry from navigation data, projecting real shot-receiver positions onto a straight processing line.
QC modules verify the integrity and completeness of the assigned geometry before processing continues. QC trace geometry checks that all expected header fields (offset, midpoint X/Y, shot and receiver coordinates) are populated and plausible. Check geometry by first breaks validates offset assignments by comparing first-break pick times against expected moveout curves, flagging traces where the assigned offset is inconsistent with the observed arrival time. QC geometry by FB provides an extended first-break QC workflow with configurable velocity and offset windows. Geometry QC azimuthal displays and analyses the azimuthal distribution of offsets within each CMP bin, which is critical for wide-azimuth and azimuthal anisotropy studies. QC panel fold shows the number of contributing traces in each bin or panel, helping identify areas of under-coverage or irregular geometry.
Several modules fill gaps in header information or derive new header values by interpolation. Create interpolation matrix builds a spatial interpolation grid from known geometry points, which is subsequently used to fill in positions for traces with missing or unreliable coordinate data. Interpolate headers from matrix applies that interpolation matrix to assign coordinates to traces whose positions were not captured in the field records. 3D interpolation regularises sparse or irregularly sampled 3D data onto a uniform receiver grid. FK Interpolation reconstructs missing or aliased traces using frequency-wavenumber domain interpolation. Flood fill cube propagates geometry values across empty bins in a 3D volume to produce a fully populated header cube.
Ghost reflections arise in marine acquisition when acoustic energy reflected from the sea surface arrives at the receiver shortly after the direct downgoing wavefield. Deghost applies a receiver-ghost removal filter in the time-offset domain, using the water depth and cable depth to design a notch-correcting operator. Tau-P deghost performs the same operation after transforming data to the tau-p (intercept time versus ray parameter) domain, where ghost energy is more easily separated by its characteristic slope. TauP Decon combines tau-p transformation with deconvolution to simultaneously suppress ghost and source-side reverberations.
Modules in this group handle non-straight 2D acquisition geometries commonly encountered in land surveys where the line follows roads or topographic features. Import Crooked Line reads a crooked line definition that describes how the actual shot and receiver positions deviate from a straight reference. Move trace vector to crooked line projects trace coordinates onto the crooked processing line so that CMP binning can be performed along the actual acquisition geometry. GUpdate Topo Crooked Line Procedure updates topographic elevation values along a crooked line after its geometry has been modified. Create Stack Line constructs a straight stack line from a crooked line survey, mapping bins onto a regularised output. Enhance gathers geometry creator synthesises geometry for enhanced gather outputs derived from pre-stack processing.
Some modules within the Geometry chapter address data conditioning tasks that are closely tied to geometry information. Adaptive ground roll noise attenuation by gather uses offset and azimuth information to design gather-specific dip filters that suppress surface-wave noise while preserving reflected arrivals. Kill empty traces zeroes out traces that have no geometry assigned or contain only noise, preventing empty-trace contamination from propagating through the flow. Shift multi-line gathers applies time shifts derived from geometry differences between acquisition lines in a multi-line recording configuration. Merge velocity gathers combines velocity-domain gathers from separate acquisition geometries into unified CMP supergathers for velocity analysis.
Several utility modules handle specific header correction and conversion tasks. FFID Fix corrects field file identifier (FFID) values in trace headers when they have been incorrectly assigned during recording or demultiplexing. GVelocity Header Creator populates velocity-related header fields derived from the geometry model, used when the velocity distribution must be encoded directly in the trace headers. Well data exchange imports or exports well location and deviation data in formats compatible with the geometry database. Well Data Show displays well positions overlaid on the processing geometry map for spatial QC. Geometry extractor from BinGrid derives shot and receiver geometry attributes from an existing bin grid model.