Raw navigation data were saved in HYPACK format (<http://www.hypack.com>). File name convention is LLL_TTTT.DDD, where LLL is the HYPACK line number, TTTT is the 24 hour time for the beginning of the file, and DDD is the Julian day. Times were recorded in UTC (Coordinate Universal Time).
The GPS navigation was significantly hindered by interference during the first leg of survey 06012 (lines l1f1 - l99f2, 4-14 Aug 2006). Frequent navigation dropouts halted data collection for extended periods during the survey.
The raw HYPACK navigation files are stored in separate directories indicating the acquisition Julian Day. The filenames in each folder are in the format of linenumber_starttime.julianday. For example, filename 014_1444.113 represents HYPACK line number 014, start time 1444 and Julian Day 113. Times are recorded in UTC (Coordinate Universal Time).
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.
FIL: Raw format file.
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: For surveys 06012 and 07001: Indicates that lines collected with device designation 1 are using Ashtech Z-Extreme, capable of recording antenna elevations above a vertical datum (i.e. real-time kinematic, RTK).
OFF: device offsets
DEV 1: For surveys 06012 and 07001: Indicates that the lines with device designation 1 are lines of Ashtech DGPS data - which was disabled for parts of these surveys.
PRD: Private Device Data (multiple formats depending on the type of device generating the data).
DEV 2: For survey 06012-leg1: Indicates that the lines with device designation 2 are lines of the motion reference unit. For surveys 06012-leg2 and 07001: Indicates that the lines with device designation 2 are lines of the single-beam echosounder.
DEV 3: For survey 06012-leg1: Indicates that the lines with device designation 3 are lines of the single-beam echosounder.
LIN 2: planned line data follows
PTS: planned line waypoints (easting and northing, UTM, zone 19N, meters)
LBP: planned line begin point (easting and northing, UTM zone 19N, meters)
LNN: planned 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 (0 for Ashtech) 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 19, 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 2=Differential GPS fix.
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 X 100; long=raw longitude X 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 surveys 06012 and 07001 there were several different messages were sent from the GPS systems: $GPGGA, $GPVTG, and $GPZDA (06012 also had $GPHDT and 06012-leg2 had $PASHR,POS and $PASHR,SAT). 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 (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.
FIX: Fix (event) mark in the format "FIX vn" where n=FIX format version number.
The (National Marine Electronics Association) NMEA strings $GPGGA, $GPVTG, $GPZDA, $GPHDT 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
$GPHDT is Actual vessel heading in degrees in format "$GPHDT,xxx.x,T" where xxx.x=heading in degrees and T indicates True Heading, checksum
Example: $GPHDT,005.533,T*35 Heading in Degrees = 5.533 True = T Checksum = *35
$PASHR,POS is Position information and $PASHR,SAT is GPS satellite tracking status information. Both are Ashtech proprietary format; no additional explanation could be found.