High-resolution multichannel seismic-reflection data acquired in the northern Gulf of Mexico, 1998-99

1998 multichannel seismic data acquisition: Acquisition and recording of air-gun and water-gun seismic reflection data. The source consisted of either a 35/35 cubic inch dual-chamber GI ("Generator-Injector") air gun or a 15 cubic inch water gun. The "injector" chamber of the GI gun was timed to discharge a short time (typically 20-30 msec) after the "generator" chamber so as to suppress the bubble pulse and create an optimal signal. The streamer was 240 meters in length with a 10-meter group interval (three hydrophones per group), and was manufactured by Innovative Transducers, Inc. (ITI) with solid-core construction and "thin-film" cylindrical hydrophones of polyvinylidene fluoride (PVDF) plastic. A problem with a streamer connection caused the far 7 channels to be very noisy, and these channels were eliminated during data processing. Data were digitized with the Geometrics Strataview seismograph and recorded with the Geometrics Marine Controller in SEG-D format.

1999 multichannel seismic data acquisition: The multichannel data acquisition equipment and parameters in 1999 were the same as 1998 except the 15 cubic inch water-gun source was used on all lines, and the recording problem with the far 7 streamer channels was corrected.

Multichannel data processing: A representative data processing sequence consisted of:

1. SEG-D input and resample to 0.5 millisecond
2. Trace edit
3. Geometry assignment
4. 50 Hz low-cut filter
5. Water-bottom mute
6. Deep-water recording delay correction
7. Spherical divergence correction
8. Noise-spike editing
9. FK filter
10. Deconvolution
11. Common midpoint (CMP) sort
12. Stacking velocity analysis
13. Normal move-out correction
14. Stack
15. SEG-Y output
16. 60-320 Hz bandpass filter
17. Whole-trace balance
18. gif image file output

Positional (navigation) data: As the seismic reflection data were acquired, the position of the vessel was continuously determined with the differnetial Global Positioning System (GPS). GPS positions were recorded approximately every second, and written to an ASCII file. This file was subsequently used to determine the position of each seismic reflection "shotpoint". This processing occurred in 199806 and 199904, with the process date reflecting the most recent of those.

The data were plotted in 8-bit gray scale representation to Postscript files using the Seismic Unix 'psimage' algorithm at a scale of 0.15 seconds per inch and 75 traces per inch. The Postscript images were then converted to GIF with Aladdin Ghostview v5.50.

Peter Schweitzer made improvements to the metadata file for inclusion into GEO-NSDI web accessible folder. Upon inspection, some of the improvements he made include: added the USGS Thesaurus and appropriate terms, added the ISO Topic Categories thesaurus and appropriate term, updated/added the publication online links (citation and cross-references), updated the browse graphic link, added a direction spatial reference method (removing the indirect spatial reference), added an entity and attribute overview description, added additional digital formats and network resource names.

Edits to the metadata were made to fix any errors that MP v 2.9.50 flagged. This is necessary to enable the metadata to be successfully harvested for various data catalogs. Minor edits to the structure of the metadata were performed such as removing extra carriage returns. The DOI link was added to the identification section as well as to some cross-references. Added additional USGS Thesaurus terms. Added the links to the field activities related to these data. Updated the currentness reference to more accurately describe the range of dates and data. No attempt was made to add detailed entity and attribute information specific to the data. The user will need to reference the original Open-File Report for that information. Added access instructions for the online resources. The metadata date (but not the metadata creator - which Peter set to himself) was edited to reflect the date of these changes. The metadata available from a harvester may supersede metadata bundled within a download file. Compare the metadata dates to determine which metadata file is most recent. Additional edits were probably made to the original metadata by someone else who did not document what they changed (20210408). Tweaked a thesaurus name (20211117).