IEDA: Marine Geoscience Data System Integrated Earth Data Applications homepage

BSR Nankai ew9907

New User Information

Initial Account Registration

You may freely explore the UTIG Academic Seismic Portal. However, an account registration is required before downloading some of the seismic data residing at UTIG. This allows for seamless handling of data requests and approvals if required by data access requirements. It also provides a method to keep track of the download cart and ftp requests. See below for how this information is used.

For immediate access, fill out the information below. Completing the form and selecting the Accept button below indicates that you have agreed to properly credit all the downloaded data and have agreed to abide by the Terms of Use.

*
*
*

*
*
*
*
*(Minimum 6 characters)
* (Confirm)
  *Please type a short explanation for why you would like an account or how you plan to use the data.
* Indicates a required field

 

top

Why Registration and Activity Tracking?

Registering is a convenient way to provide access to data that is restricted by keying registration to select files, groups of files, or cruises after approval has been given by the data contributor.

Tracking summaries are provided to scientists responsible for submitting data. Data contributors are more likely to participate if they get feedback on usage of data they collected, processed or interpreted.

Downloading activity allows us to to derive activity statistics which are used in justifications to funding agencies. More funding means a better database and website.

We do not share email addresses with anyone other than the responsible scientist. None of the information is shared with any commercial enterprise, and we adhere to University privacy policies.

The Data Center handles public, access-restricted and proprietary data. There are no restrictions on the metadata. Access to restricted data is by registration/login after the approval of the data contributor.

- Access restrictions are maintained until the contributors approve release. These are principally governed by NSF data-sharing policies.

- Access to proprietary data is determined by the contributing institution including negotiating terms, conditions and cost.

Data are provided with the express understanding that they will not be sold or given to third parties. Data are not provided for inclusion with other commercial databases or web sites without prior written approval.

top

Navigation and Trace Positioning

Navigation
The 'field' or cruise navigation will typically be a time series though not necessarily a position for every shot or common mid-point. Time series files may be segmented and line-ordered or time-ordered. Navigation for much of the older data is relatively poor by present standards and unsuitable for some purposes.

Shot navigation is in a variety of forms and quality related to historical methods of navigation and data logging. An important part of the information is whether the navigation is associated with the antenna position or if offsets have already been included to provide the position of the source, usually tens of meters offset in both x and y. With few exceptions most older navigation do not contain this offset.

Trace Positions
Locations of stacked or processed traces are included in the SEG-Y trace headers and as ASCII files. Proper geographical location of processed data requires a correlation between external navigation and the processed (e.g., sorted and stacked) trace. To do this precisely requires information on how the data were sorted, the source-to-receiver offsets, antenna-to-source offsets and ship's heading. Cruise reports and information pages summarize this information when available.

top

Seismic Data

Seismic Data
SEG-Y formats are supported with enough information for reprocessing. On board the R/V Langseth, LDEO records the shipboard data in SEG-D format as tarfiles.

Older multiplexed shot data were normally converted to trace sequential form as a first step for data processing. Along the way new tape numbers were generated and various shot/record/sequence numbers are translated and placed in the SEG-Y headers, not always consistently, and with some numbers resetting to 0 or 1  (e.g., after 999, 4095 and 9999). Thus, direct mapping back to the shipboard handwritten logs is sometimes difficult.

Some Rules:

File naming convention should assume case-sensitivity.

Line Names
Any number-letter combination and hyphen and underscore are acceptable. No other special characters or spaces are acceptable. Often field lines are joined or subdivided during processing, so AN-16 could also be AN-16A, AN-16B, AN-15_17, AN-16B2. Thus, a separate table is required for line names.

Cruise Names
Presently we use informal abbreviations like EW0005, FM3502. Many cruises have no NGDC identifications.

Navigation
Navigation must exist for each shot line, otherwise SEG-Y shot data is not included in the DMS. Trace locations must exist for each processed line, otherwise the SEG-Y data is not included (Exception: 3-D volumes). Multiple processed versions of a line each have their own trace location file (.cmp). We have examples with different sort geometries and therefore different trace locations.

Some modern data include positions, date and time in the shot headers. Older data do not. Navigation is placed into the SEG-Y headers for all stacked or otherwise processed data. Also provided are ASCII navigation files with the same information.

SEG-Y formats and EXCEPTIONS
Most SEG-Y variations are defined by the SEG-Y format at http://www.seg.org/publications/tech-stand/. At the Marine Seismic Data Center at UTIG, we tend to rely on the information in the individual trace headers and do not actually check the 'tape header' except for sample format.

- Exception 1 Exception 1: We rely on use of the binary reel header where the sample format is coded according to SEG specifications. We do use the SEGY-Y revison 1 convention (where format code=5 is IEEE 32-bit floating point). Most processed files are IBM 32-bit floating point (=1) or IEEE 32-bit floating point (=5). Older shot data often use other SEG-Y defined formats.

- Exception 2 : UTIG OBS trace headers contain a 32-bit millisecond delay at byte 107 instead of the SEGY standard 16-bit number at byte 109. This is in a header location and an attribute of the OBS table.

-Exception 3 : UTIG uses byte 167 for milliseconds instead of gmt/local time indicator.

top

Archive History

The original UTIG archive was built around the historical path of tape storage: 9-track, Exabyte 8000 series, DLT 7000 and Exabyte M2. At the DLT translation we began the database effort and a naming system for files, arxx.xxxx, where the prefix relates to DLT tape number and the suffix to a file number. We have moved to an automated storage system and SAM-FS software for file access retaining the file naming convention since it is so pervasive in our database and PHP coding.

top