The times recorded in the navigation file are in UTC. Keywords and the information they provide 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 vessel name, agencies involved with the survey, and the location of the survey.
ELL: Ellipsoid information. The name of the ellipsoid followed by the semi-major axis in meters and the flattening ratio.
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: For survey 2014-002-FA: Indicates that lines collected with device designation 0 are lines of Differential Global Positioning System (DGPS) collected with the Hemisphere DGPS receiver. When sampling began and geophysical surveying ended on Julian Day 203. The Hemisphere DGPS was disabled at DEV 0 and enabled as a DEV 5 with an offset to relocate the GPS at the stern of the vessel where the sampler was being deployed. All files ending in ***.203 and later will have a DEV 5.
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.
PRD: Private Device Data, which has multiple formats depending onf the type of device generating the data. KTD for is example is a Kinematic Tide Datum File.
DDT: identifies the device that the computer clock is being synchronized to.
DEV 1: For survey 2014-002-FA: Indicates that the device designation 1 is a web-interface that is relaying the hypack feed from the acquisition van to a bridge monitor and the processing van.
DEV 2: For survey 2014-002-FA: Indicates that the lines with device designation 1 are lines of Real Time Kinematic Global Positioning System (RTK-GPS) data collected with the Ashtech ProFlex 800 GPS RTK receiver. This device recorded the RTK-GPS heights and was capable of recording antenna elevations above a vertical datum (Kinematic Tide Datum).
DEV 3: For survey 2014-002-FA: Indicates that the lines with device designation 3 are lines of fathometer information collected by a Sitex DepthFinder. This device is utilized by the MVP30 to transmit depth measurements ensuring that the sound velocity profiler would not deploy below 4 meters from the sea floor.
DEV 4: For survey 2014-002-FA: Indicates the device designation 4 are NMEA Output lines.
DEV 5: For survey 2014-002-FA: indicates that the device designation 5 are also lines of Hemisphere DGPS, but only during 3 days at the end of the survey when samples were being collected. The DEV 0 hemisphere was disables and became DEV 5 with an offset (-13) to the stern as a backup for sample location.
LIN 2: planned line data follows
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 or 5 for Hemisphere 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 2014-002-FA there were several different messages were sent from the GPS systems: $GPGGA, $GPVTG, and $SDDPT were standard throughout the survey. 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.
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.
KTC: Describes how HYPACK records water levels (tide corrections) when using RTK where “KTC dn t nv eh lh u kval offset draft final” where dn = device number, t=time tag (seconds past midnight, matches GPS position), nv=number of values, eh= WGS84ellipsoidal height (from GPS), lh= local ellipsoidal height (on local ellipsoid), u=undulation, kval= K value, offset= antenna offset, draft=draft correction, final=final tide.
The (National Marine Electronics Association) NMEA strings $GPGGA, $GPVTG, $SDDPT 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,160209.00,3806.336689,N,07505.875090,W,4,11,0.9,5.038,M,-36.840,M,1,0378*61 UTC Time = 160209.00 Latitude = 3806.336689 N Longitude = 07505.875090 W Fix Quality = 4 (indicates RTK) Number of satellites = 11 HDOP = 0.9 relative accuracy of horizontal position Altitude = 5.038 meters above mean sea level Height of geoid above WGS84 ellipsoid = -36.840 meters Time since last update = 01 Checksum = *61.
$GPVTG is track made good and ground speed in the format "$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
$SDDPT is Depth Below the EchoSounder (Sitex)Transducer in the format "$SDDPT,x.x,x.x,F*CS" where x.x=depth in meters, x.x=offset from transducer: positive is distance from transducer to water line, or neative is distance from transducer to keel.
Example: $SDDPT,3.6,0.0*52 Depth in Meters = 3.6, Offset from transducer = 0.0., CRC Checksum of NMEA data = 0.0*52.