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                           NAVIGATION FIELD DATA

                                Description

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The directory rawnav located in directory nav contains the raw navigation
that was collected during the sidescan-sonar component of the field program
using a USGS differential GPS system (Ashtech). These files represent the
data that was originally recorded on floppy disk aboard ship. The data are
in NEMA format, but only contain the $GPGGA string. WARNING: These data
have not been checked for errors. Use with caution.

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To aid viewing of the original raw navigation data, each data entry was
reformatted (removing the NEMA codes) by filtering the raw data files
through a UNIX awk script. (see README). Every navigation fix from the
original data has been preserved, however.

The navigation is stored in ASCII files using six fields separated by tabs,
with each file representing a separate julian day (i.e. jd128web.txt).
Navigation fixes are at 10 second intervals. These files are located in the
NAV sub-directory.

   * Field 1: date and time (julian day:hour (UTC):minute:second)
   * Field 2: Latitude (ie. 32d59.375 = 32 Degrees 59.375' North)
   * Field 3: Longitude (ie. -79d96.875 = 79 Degrees 96.875' West)
   * Field 4: Speed (in knots, computed from the navigation)
   * Field 5: Heading (in degrees, computed from the navigation, i.e.
     course made good)
   * Field 6: Water Depth (derived from a Furuno dual-frequency
     fathometer). Depths are in meters, but have not been corrected for the
     depth of the transducer, roughly 2 m below the sea surface, nor for
     the tide (for tidal information and 6 minute tidal data, see NOAA's
     tide server).

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    [Image] To Navigation Field data                         [Image] To
                         Sidescan-Sonar Field data

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