SEG‑D Viewer Tips: Troubleshooting, Performance, and ExportingSEG‑D is the industry standard format for raw seismic field data recording. Its flexibility and richness make it indispensable for seismic acquisition, but those same qualities can introduce complexity when viewing, troubleshooting, and exporting data. This guide collects practical tips for working with SEG‑D viewers: diagnosing common problems, improving performance with large files, and exporting clean, usable data for processing or delivery.
Understanding SEG‑D basics
SEG‑D files store multichannel, time‑sampled seismic traces along with a variety of headers and auxiliary records (e.g., shot location, instrument configuration, telemetry metadata). Several SEG‑D revisions exist, and vendors often embed proprietary or nonstandard extensions. Knowing which SEG‑D revision and vendor-specific quirks you’re dealing with is the first step toward successful viewing and export.
- Check the revision and vendor: Many viewers display the SEG‑D revision (e.g., 0, 1, 2, 3) and recorder type in file metadata. If your viewer misinterprets headers, it may not support that revision or vendor extension.
- Recognize wrapper formats: Some systems wrap SEG‑D inside other containers or compress it; a viewer that reads raw SEG‑D may fail on wrapped files.
- Header structure matters: Trace headers, channel maps, and blockette definitions determine how samples are interpreted — wrong interpretations lead to swapped channels, incorrect sample rates, or misaligned traces.
Troubleshooting common viewer issues
- File won’t open or errors on load
- Verify the file is complete (no interrupted transfers). Use file-size expectations from acquisition logs.
- Try opening with a different SEG‑D viewer to isolate whether the file or the viewer is at fault.
- If the viewer reports an unsupported revision or blockette, consult the acquisition vendor for a compatible reader or a conversion utility.
- Trace timing or sample-rate problems
- Confirm sample rate and number of samples per trace in the file header. Misread sample rates often cause vertically stretched or squashed displays.
- Check for inter-record gaps or padding records inserted by acquisition systems; these can shift trace timing unless the viewer accounts for them.
- Channels missing or misnumbered
- Examine channel maps and header blockettes that define channel numbering and active channels. Vendor-specific numbering schemes (e.g., 0‑based vs 1‑based) can cause mis-labeling.
- Look for disabled channels in the array or masked channels in the file that some viewers omit by default.
- Incorrect instrument polarity or units
- Polarity inversion can come from acquisition wiring or misinterpreted scale factors in headers. Apply a sign flip or adjust scale factors when exporting or processing.
- Verify ADC counts vs physical units (e.g., volts, mV/g). Some viewers show raw counts by default—apply proper calibration to get physical units.
- Corrupted or partially overwritten headers
- Use hex viewers or specialized SEG‑D repair tools to inspect blockette integrity. If header corruption is confined and trace payloads are intact, reconstituting headers may restore usability.
- Maintain hashes (e.g., SHA256) of original acquisition files so you can detect corruption after transfer.
Performance: working with large SEG‑D datasets
Large surveys produce SEG‑D files that can be tens or hundreds of gigabytes. Efficient viewing and export require both software and workflow strategies.
- Choose a viewer optimized for large files
- Look for viewers that use memory‑mapped I/O or streaming reads rather than loading entire files into RAM.
- GPU acceleration for rendering can dramatically improve interactive scrolling and zooming.
- Use selective loading and downsampling
- Load only header indices or selected channel ranges when scanning files.
- For quick inspection, use downsampled previews (decimated traces) and load full resolution only for areas of interest.
- Parallelize processing
- When exporting or converting, break files into record or shot‑based chunks and process in parallel workers. Ensure the viewer or conversion tool preserves continuity across chunk boundaries when required.
- Optimize storage and I/O
- Keep data on fast local SSDs when possible. For network storage, use high‑throughput links (10GbE or higher) and ensure the viewer can read over file protocols efficiently.
- Use compressed SEG‑D variants supported by your tools to reduce I/O, but balance CPU decompression cost against I/O savings.
- Monitor resource usage
- Track memory, CPU, and I/O; if the viewer thrashes or stalls, increase RAM or switch to streaming modes. Some viewers provide diagnostic logs to tune buffer sizes and thread counts.
Exporting: formats, fidelity, and metadata preservation
Exporting from SEG‑D to processing-friendly formats (e.g., SEG‑Y, MiniSEED, SAC, CSV) is common. Key concerns are numerical fidelity, timing accuracy, and metadata preservation.
- Choose the right target format
- SEG‑Y: standard for processed seismic; preserves trace data and rich headers but requires correct header mapping.
- MiniSEED: compact for continuous time series and seismic networks; good for telemetry and ambient data.
- SAC: favored in academic seismology; includes its own header schema for events and stations.
- CSV/ASCII: useful for quick checks but loses binary fidelity and many metadata fields.
- Preserve sample rate and timing
- Ensure sample rate, start time, and any inter-record gaps are translated exactly. For time‑sensitive workflows (e.g., VSP, source‑synchronization), verify absolute timing against acquisition logs.
- Map headers thoughtfully
- Create a header mapping table beforehand: which SEG‑D blockettes/fields map to SEG‑Y trace headers or target format attributes. Preserve important fields like channel number, instrument gain, sensor ID, shot/record number, and geolocation when available.
- Maintain scaling and units
- Apply calibration constants from the SEG‑D headers so exported traces reflect physical units (e.g., volts or acceleration) rather than raw ADC counts, unless raw counts are intentionally required.
- Embed provenance metadata
- Include processing history, software/version, export parameters, and original file identifiers in the exported file headers or sidecar files. This prevents downstream confusion and facilitates reproducibility.
- Validate exports
- After export, spot‑check waveform shapes, amplitude statistics, and header fields against the original SEG‑D. Use checksums or hashes on exported chunks to ensure integrity.
Practical workflows and example commands
- Quick inspection:
- Open a viewer in “header index” mode, list revisions and channel maps, then preview decimated traces.
- Batch conversion:
- Split large SEG‑D into shot‑aligned chunks, run parallel converters to SEG‑Y, then reassemble or index outputs for the processing system.
- Calibration and unit conversion:
- Extract gain/scale factors from headers, apply to traces during export, and write units into target headers.
Example (conceptual) pipeline:
- parse_headers(segd_file) -> build index
- for each shot_chunk in parallel: read_chunk -> apply_calibration -> write_segy(chunk)
- validate_segy_against_index -> record_provenance
Vendor and viewer quirks to watch for
- Proprietary blockettes: Some vendors add custom blockettes that store extra metadata (e.g., GPS, telemetry). Confirm your viewer supports or can be extended to read them.
- Byte order and encoding: Watch for nonstandard endianness or uncommon sample encodings (e.g., 32-bit IBM float vs IEEE float vs integer).
- Multi‑tape or segmented files: Some systems split acquisitions across multiple files with overlapping headers—ensure your viewer can logically concatenate or index them.
Best practices checklist
- Always keep original SEG‑D files intact; work on copies.
- Record checksums and transfer logs after field acquisition.
- Know your viewer’s supported SEG‑D revisions and vendor compatibility.
- Use streaming, selective loading, and parallel export to handle large datasets.
- Verify calibration, header mapping, and timing during export.
- Embed provenance and validate outputs.
If you want, I can:
- Provide a sample header‑mapping table (SEG‑D → SEG‑Y) tailored to a specific SEG‑D revision or vendor.
- Recommend specific SEG‑D viewers and conversion tools for Windows/Linux/macOS.
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