The times recorded in the navigation file are in UTC. The SDDBT and EC1 messages, although present in many of the HYPACK files, are invalid. Keywords and the information they provide are as follows:
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. NOTE: survey area is listed as "Vineyard Sound/MV" which is incorrect. The survey area was offshore of Fire Island, New York.
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 -75 indicates UTM, zone 18.
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 lines collected with device designation 0 are lines of Differential Global Positioning System (DGPS) collected with the Ashtech BRG2 receiver. The label for this device was "DGPS" throughout this survey.
OFF: Device Offsets in the format "OFF dn n1 n2 n3 n4 n5 n6 n7" where dn = device number; n1 = starboard or port offset (positive starboard); n2 = forward or aft offset (positive forward); n3 = height (antenna) or depth (transducer draft) offset; n4 = yaw rotation angle (positive for clockwise rotation); n5 = roll rotation angle (port side up is positive); n6 = pitch rotation angle (bow up is positive); n7 = device latency in seconds.
DDT:identifies the device synchronizing the computer's time.
DEV 1: Indicates that the lines with device designation 1 are lines of Real Time Kinematic Global Positioning System (RTK-GPS) data collected with the NovAtel DL-V3 receiver - note: this device was labeled "DLV3" throughout this survey. This device recorded the RTK-GPS heights and was capable of recording antenna elevations above a vertical datum.
DEV 2: Indicates that the lines with device designation 2 are lines of RTK-GPS collected by the Ashtech Z-Extreme receiver; note: this device was labeled "AshtZ" throughout this survey.
DEV 3: Indicates that the lines with device designation 3 are lines of bathymetry information collected by an UNKNOWN device; note: this device was labeled "Bathy" throughout this survey. This was a dummy depth feed used by HYPACK during acquisition to plot recent survey line history to ensure that completed survey lines were not re-surveyed.
DEV 4: Indicates that the lines with device designation 4 are lines of instrument information "Octopus F180" had it actually been recording any data; note: this device was labeled "Disabled" throughout the survey.
LIN 3: planned line data follows where X indicates the number of waypoints
PTS: planned line waypoints (easting and northing, UTM, zone 18N, meters)
LBP: planned line begin point (easting and northing, UTM zone 18N, meters)
LNN: planned line name
EOL: end of planned line
USR: user information
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 (0 for Ashtech BRG2 DGPS) 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. Not all data types were recorded in each HYPACK file.
POS: Position of the ship in the format "POS dn t x y" where dn=device number; t=time tag (seconds past midnight); x=easting; y=northing. On this cruise these values are in UTM, Zone 18, 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) where 0 = fix not available or invalid; 1 = GPS fix; 2 = Differential GPS fix; 3 = GPS PPS Mode fix; 4 = RTK fix; and 5 = RTK Float. The last 3 values are decoded from GST message: standard deviation of latitude error (meters); standard deviation of longitude error (meters); Standard deviation of semi-major axis of error ellipsis (meters).
RAW: Position information in the format "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.
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. During survey 2011-005-FA there were several different messages were sent from the GPS systems: $GPGGA, $GPVTG, $GPZDA and $SDDBT were standard throughout the survey. Message $SDDBT appears to be invalid. These message strings will be defined below.
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 (singe frequency) in the format "EC1 dn t rd" where dn=device number, t=time tag (seconds past midnight), rd=raw depth. ** These values are not valid.
GYR: Gyro data (heading) in the format "GYR dn t h" where dn=device number, t=time tag (seconds past midnight), h=heading.
HCP: Heave Compensation in the format "HCP dn t h r p" where dn=device number, t=time tag (seconds past midnight), h=heave in meters, r=roll in degrees (+ port side up), p=pitch in degrees (+ bow up).
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 $GPGGA, $GPVTG, $GPZDA, $SDDBT are stored in the HYPACK file. 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.
$GPVTG is track made good and ground speed in the format "$GPVTG, true, T, mag, M, grsp1, N, grsp2, K, mode", where t=true course made good over ground in degrees, T= True, m=magnetic course made good over ground in degrees, M=magnetic, grsp1=ground speed, N=Knots, grsp2=ground speed, K=Kilometers per hour, mode=Mode indicator (A=Autonomous, D=Differential, E=Estimated, N=Data not valid).
Example: $GPVTG,340.39,T,356.37,M,005.50,N,010.18,K,D*27
True course made good: 340.39 Magnetic course made good: 356.37 Ground speed (knots) = 5.5 Ground speed (kilometers) = 10.18 Mode=Differential
$GPZDA is UTC Date/Time and Local Time Zone Offset in the format "$GPZDA,hhmmss.ss,xx,xx,xxxx,xx,xx" where hhmmss.ss=UTC, xx=Day, 01 to 31, xx=month, 01 to 12, xxx=Year, xx=Local zone description, 00 to +/- 13 hours, xx=Local zone minutes description (same sign as hours), checksum.
Example: $GPZDA,173357.00,28,04,2007,,*69
UTC= 173357.00 UTC day = 28 UTC month = 04 UTM year = 2007 Local zone hours = null Local zone minutes = null Checksum = *69
$SDDBT is Depth Below the Transducer in the format "$SDDBT,xxx.x,f,xxx.x,M,xxx.x,F*CS" where xxx.x=depth in feet, xxx.x=depth in meters and xxx.x=depth in fathoms). Note: this NMEA message appears to be invalid throughout these surveys as this was a dummy depth feed used to plot survey history in the HYPACK real-time display.
Example: $SDDBT,6.6,f,2.0,M,1.1,F
Depth in Feet = 6.6 Depth in Meters = 2.0 Depth in Fathoms = 1.1