The times recorded in the navigation file are in UTC. Keyword definitions and the information listed below are comprehensive and not found in every file. The definitions are as follows:
FTP: The first record located at the top of the header used to identify the file format.
VER: HYPACK version number.
INF: General survey information filled in by the data technician. This typically contains the survey participants, the vessel name, other agencies involved with the survey, and the location of the survey. The three numbers at the end refer to initial tide correction at start-of-line, initial draft correction at start-of-line and sound velocity from the navigation parameters.
FIL: Raw format file. In the HYPACK files this line suggests that the data were collected in Penobscott Bay, however, this is an inaccurate entry left over from a previous cruise.
ELL: Ellipsoid information. The name of the ellipsoid followed by the semi-major axis in meters and the flattening ration.
PRO: Project information record where TME indicates Transverse Mercator and the central meridian of -69 indicates UTM, zone 19.
DTM: Datum transformation record
GEO: Geoid model. Blank if not present.
HVU: Horizontal and Vertical Units (meters).
TND: Survey time and date in UTC.
DEV 0: Indicates that the lines with device designation 0 are lines of DGPS data acquired with a Communications Systems International (CSI), Inc. LGBX Pro (single frequency) receiver.
OFF 0: device offsets for device 0. Format of the value is OFF dn n1 n2 n3 n4 n5 n6 n7 where dn=device number; n1=starboard, port offsets where positive is starboard; n2=forward, aft offset where positive is forward; n3=height (antenna) or depth (transducer draft) offset - always positive; n4=yaw rotation angle where positive for clockwise rotation; n5=roll rotation angle where port side up is positive; n6=pitch rotation angle where bow up is positive; n7=device latency in seconds. No offset for device 0 during this data collection.
DEV 1: Indicates that the lines with device designation 1 are lines of DGPS data acquired with a Garmin 5312 (single frequency, echosounder) receiver
OFF 1: device offsets, where the antenna is offset 0.6 meters
DEV 2: Indicates that the lines with device designation 1 are lines of RTK data acquired with the Novatel DLV3 (RTK) receiver.
OFF 2: device offsets, where the antenna is offset -2.57 meters
DDT 2: identifies the device (2) that the computer clock is being synchronized to.
LIN: planned line data follows in the format "LIN nw" where nw=number of waypoints.
PTS: planned line waypoints; easting, northing in UTM zone 19N, meters.
LBP: planned line begin point; easting, northing in UTM zone 19N, meters.
LNN X: planned line name where X is the line name
EOL: end of planned line
EOH: end of header
The remaining elements have similar information in the first 3 columns. The first column will indicate the data type, the second column will indicate the device that recorded the information (e.g. 0 for Ashtech Z-Extreme receiver) and the third column is the time tag (seconds past midnight) that is also sometimes referred to as the latency. The remaining information on each line is specific to the data type.
POS: Position of the ship - in this case the antenna - in the format "POS dn t x y z" where dn=device number; t=time tag (seconds past midnight); x=easting; y=northing. On this cruise these values are in UTM, Zone 19N, WGS84.
QUA: Position quality information in the format "QUA dn t n m h sat mode" where dn=device number; t=time tag (seconds past midnight); n=number of values to follow; m = 10 minus HDOP (horizontal dilution of precision); h=HDOP; sat=number of satellites; mode=GPS mode (NMEA 0183 standard values)
RAW: dn t n lat long alt utc" where dn=device number; t=time tag (seconds past midnight); n=number of values to follow; lat=raw latitude in the format ddmmmm.mmmm. To convert to ddmm.mmmmm multiply by 100; long=raw longitude in the format ddmmmm.mmmm. To convert to ddmm.mmmmm multiply by 100; alt=antenna altitude above ellipsoid (meters); utc=GPS time in the format HHMM
GYR: Gyro Data (heading) in the format "GYR dn t h" where dn=device number; t=time tag (seconds past midnight); h=shipheading angle.
MSG: Message string in the format "MSG dn t message" where dn=device number; t=time tag (seconds past midnight); message is the message sent from the device. On this cruise, five different messages were sent from the DGPS: $GPGGA, , $SDDPT. These will be defined later.
TID: Tide correction in the format "TID dn t dc" where dn=device number, t=time tag (seconds past midnight), dc = draft correction.
EC1: Echo Sounding (single frequency) in the format "EC1 dn t rd" where dn=device number; t=time tag (seconds past midnight); rd=raw depth in meters.
FIX: events marked manually by the user in the format "FIX dn t event_number" where dn=device number (typically 99 as there is no device for manual events); t=time tag (seconds past midnight); event_number=event number such as 1,2,3,4.
The National Marine Electronics Association (NMEA) strings present in the HYPACK file are the $SDDPT and $GPGGA. These are defined as follows:
$GPGGA is GPS fix data in the format "$GPGGA, t, lat, lath, long, longh, q, sat, h, a, M, alt, M, t2, refcheck" where t=time in UTC in the format hhmmss.ss; lat=latitude in the format ddmm.mmmmmm; lath= N or S indicating the latitude hemisphere; long=longitude in the format dddmm.mmmmmm; longh=E or W indicating the hemisphere; q=fix quality where 0=fix not available or invalid; 1=GPS fix; 2=Differential GPS fix; 3=GPS PPS Mode fix; 4=RTK fix; 5=RTK float; sat=number of satellites; h=Horizontal Dilution of Precision (HDOP); a=Antenna altitude above mean sea level (geoid); M= units of antenna altitude in meters; alt=height of geoid above WGS84 ellipsoid; M=units of geoidal height in meters; t2=time since last DGPS update; refcheck=DGPS reference station id and the checksum.
Example: $GPGGA,173356.00,4204.848996,N,07036.929067,W,4,09,01.1,00003.278,M,-028.888,M,01,0000*56 UTC Time = 173356 Latitude = 4204.848996 N Longitude = 7036.929067 W Fix Quality = 4 (indicates RTK) Number of satellites = 9 HDOP = 01.1 relative accuracy of horizontal position Altitude = 3.278 meters above mean sea level Height of geoid above WGS84 ellipsoid = -28.888 meters Time since last update = 01 Checksum = *57.
$SDDPT is water depth relative to the transducer in meters in the format "$SDDPT, data_meters, offset_meters, checksum.
Example: $SDDPT,3.71,0.50*57 Depth in meters = 3.71 Offset from transducer: Positive - distance from transducer to water line, or Negative - distance from transducer to keel ((this definition from <http://www.gpsinformation.org/dale/nmea.htm#nmea