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U.S. Geological Survey Data Series 652

Navigation Data and Maps


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Trackline Maps

Trackline maps were created with ESRI ArcGIS 9.2 software, exported to Adobe Illustrator for further editing, and saved in JPEG format. These images can be accessed through the links provided below or from within the cruisenav folder. The navigation data used to create these maps have not been corrected for the offset between the shotpoint and GPS antenna (figure 1). For more information about the GIS project, refer to the Software page.

The trackline maps contain links to geospatial profiles. The line navigation maps, which have been corrected for the GPS offset, were created with CTI SonarWeb software and are stored in the linenav folder. Refer to the Profiles page for more information about the geospatial and printable profiles.

Serious problems were noticed with the GPS data for 97FGS01, and many of these errors could not be edited from the navigation files. Several lines are missing navigation at the start of line, end of line, or within the line, and spurious data points remain. Use these data with caution. Navigation is not available for line sb_b64_b. On the trackline maps, the location of missing navigation data within a line is inferred by linear interpolation of the first and last known data points. A dashed yellow line indicates a navigation gap of 1.5 minutes or more. A cross marks the location of the first available navigation fix for lines missing navigation for the first 100 shots or more at the start of line. Asterisks mark the locations of spurious navigation fixes or missing navigation at the end of a line. Navigation is also intermittent for several 96FGS01 lines.

All 96FGS01 lines appear on the Area A map. Refer to table 3 for a list of which 97FGS01 lines appear on each of the inset maps.

Full Survey Area Map (figure 2)


Processed Shotpoint Navigation

Shotpoint navigation files and 500-shot-interval location files were extracted from the trace headers of each line using Seismic Unix software. These files were edited to remove or correct spurious data points; however, serious errors remain (refer to the Trackline Maps section above for more information). The edited navigation data were then processed with PROJ.4 software (http://trac.osgeo.org/proj/) to generate UTM coordinates from latitude and longitude coordinates and reformatted for use with ESRI GIS software. The processed navigation data have not been corrected for the offsets between the shotpoint and GPS antenna (figure 1).

The processed shotpoint navigation and 500-shot-interval location files can be accessed through the links provided below or from within the navigation folder. Each ASCII text file contains eight fields separated by commas and defined as follows:

Field 1: UTM X (Zone 17N)
Field 2: UTM Y (Zone 17N)
Field 3: Trackline Number
Field 4: Shotpoint Number
Field 5: Longitude (decimal degrees)
Field 6: Latitude (decimal degrees)
Field 7: Year
Field 8: DOY:HR:MIN:SEC (UTC)

Processed Shotpoint Navigation
96fgs01 (2-MB ASCII text file)
97fgs01 (7.8-MB ASCII text file)

Processed 500-Shot-Interval Location Navigation
s96fgs01 (33-KB ASCII text file)
s97fgs01 (193-KB ASCII text file)


Raw Shotpoint Navigation

Shotpoint navigation files were extracted from the trace headers of each line using Seismic Unix software. Unprocessed navigation files are stored as ASCII text files in the rawsegynav folder. These navigation files contain serious errors and have not been edited for spurious data points or corrected for the offset between the shotpoint and GPS antenna. Each file contains six fields separated by a space and defined as follows:

Field 1: Trackline Number
Field 2: Shotpoint Number
Field 3: Longitude (decimal degrees)
Field 4: Latitude (decimal degrees)
Field 5: Year
Field 6: DOY:HR:MIN:SEC (UTC)


Raw Delph Navigation

The navigation was recorded in the SEG Y trace headers in both the "source coordinates" location in bytes 73-80 and the "unassigned" fields in bytes 181-240. However, the "unassigned" fields are erased by SU when it processes the data. The navigation data in the defined fields are accurate to 1 s of arc, or 30.8 m. The data in the "unassigned" fields are accurate to the accuracy of the GPS receiver, or 3-5 m. We used Delph Seismic software to strip off the navigation from the unassigned fields and provide it here. However, this was done before the long lines were divided, and therefore some SEG Y filenames and shot numbers therefore do not match (Delph Seismic software is no longer available). To reconstruct them, the first 20,000 shots belong to the "linename"_a.tra file. Shots greater than or equal to 20,001 belong to the "linename"_b.tra file. The navigation data are stored in the rawdelphnav folder. Each file contains nine fields separated by a space and defined as follows:

Field 1: Shotpoint Number
Field 2: Longitude (decimal degrees)
Field 3: Latitude (decimal degrees)
Field 4: Heading
Field 5: Speed
Field 6: Fix Number
Field 7: Fish Altitude
Field 8: Date
Field 9: HR:MIN:SEC (UTC)


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