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U.S. Geological Survey Data Series 428

Navigation Data and Maps


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Raw Shotpoint Navigation

As the seismic reflection data were acquired, the position of the R/V Gyre was recorded using an integrated system consisting of LOng RAnge Navigation (LORAN)-C, satellite, and gyrocompass. The R/V Carancahua used only LORAN-C. The accuracy of the LORAN-C varied from 528 to 1,320 ft, with repeatable accuracy between 60 and 300 ft (http://www.navcen.uscg.gov/loran/handbook/h-book.htm).

Positions were recorded in latitude and longitude coordinates every 5 minutes (min) and appear on the seismic profiles as incremental, hand-annotated vertical event marks. Navigation data were obtained as .dat files, opened using Notepad, and saved as tab-deliminated text files with seven fields separated into columns:

Field 1: D (DOY, Day of Year)
Field 2: H (Hour)
Field 3: M (Minute)
Field 4: LAT (Latitude, Decimal Degrees)
Field 5: LONG (Longitude, Decimal Degrees)
Field 6: ADTA (Annotated Shot Number)
Field 7: LINE (Trackline Number or Name)

81CA1 Annotated Navigation Fixes (33-KB TXT)

81GY6 Annotated Navigation Fixes (297-KB TXT)


Processed Shotpoint Navigation

Raw shotpoint navigation data were formatted for use with ESRI ArcGIS 9.2 software and projected in WGS84 to visually inspect shotpoint accuracy. Point locations were checked against written notes made on the paper records and in the cruise logbooks. Any errors were identified, reviewed, and rectified. Hour and minute values were not altered from the format in the original data files. Attribute information was updated to include the USGS-Woods Hole field activity ID and the new USGS-St. Petersburg MASH cruise ID, and to identify if the survey had been continuous or split into legs. Each processed Microsoft Excel navigation file contained 13 fields separated into columns and defined as follows:

Field 1: DATE (Month, Calendar Day, Year)
Field 2: D (DOY, Day of Year)
Field 3: H (Hour)
Field 4: M (Minute)
Field 5: LAT (Latitude, Decimal Degrees)
Field 6: LONG (Longitude, Decimal Degrees)
Field 7: CRUISE (USGS-St. Petersburg MASH Cruise ID)
Field 8: FIELD_ACT (USGS-Woods Hole Field Activity Number)
Field 9: METHOD (Data Collection Device)
Field 10: LEG (Cruise Leg)
Field 11: LINE (Trackline Number or Name)
Field 12: SHOT (Annotated Shot Number)
Field 13: LINE_SEG (Trackline Segment Name)

81CA1 Processed Shotpoint Navigation (189-KB Excel file)

81GY6 Processed Shotpoint Navigation (1534-KB Excel file)


Trackline Maps

Three point-shapefile layers were created: all navigation shots (81CA1 and 81GY6_POINTS.shp), start-of-line shots (81CA1 and 81GY6_FIRST.shp), and start-of-segment shots (81CA1 and 81GY6_SEGMENT.shp). A trackline shapefile (81CA1 and 81GY6_LINES.shp) was generated from the POINTS.shp file using the 'locations to paths' function in Hawth's Analysis Tools (free for download at www.spatialecology.com). It should be noted that the ship's track between points is assumed to be a straight line. The attribute tables of the LINES.shp files were manually updated with information for CRUISE and LEG.

The trackline maps provided in this archive were created using ESRI ArcGIS 9.2 software and then exported to Adobe Illustrator CS2 for further editing. See the readme.txt file in the ARC folder for more details. The maps were later converted into JPEG format by Adobe GoLive. The Gulf States shoreline polygon was derived from a 1:70,000 vector coastline map of the United States originated by NOAA, 1994. The bathymetry line layer, with 100-m contours supplemented by 20-m contours on the continental shelf, was originated by NOAA, date unknown. The USGS is the originator of all other layers used. These images can be accessed through the links provided below or from within the CRUISENAV folder.

The trackline maps provided below contain links to the printable profiles, which can also be accessed from the Profiles page.

81CA1_81GY6 Location Map

81CA1 Location Map

81GY6 Location Map


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