Dataset Title: Nathaniel B. Palmer MGD77 Data Cruise:NBP03-04a Contact: Jim Swift UCSD/SIO, 0214 9500 Gilman Dr. La Jolla, CA, USA 92093-0214 Phone:(619)534-3387 Fax:(619)534-7383 jswift@ucsd.edu Dataset Description: The MGD77 data set is contained in a single file for the entire cruise. It can be found in the top level of the distribution data structure as 304A.mgd. Also at the root level, 304A.gmt is the output of the mgd77togmt utility using 304A.mgd as input. The 304A.gmt file can be used by GMT (Generic Mapping Tool) plotting software. The data used to produce the 304A.mgd file can be found on the distribution media in the file /process/304AMGD.tar. The data files in the archive contain a day's data and follow the naming convention Dddd.fnl.gz, where ddd is the year-day. These files follow a space-delimited columnar format that may be more accessible for some purposes. They contain data at one-second intervals rather than one minute and are individually "gzipped" to save space. Below is a detailed description of the MGD77 data set format. The other files in the archive contain interim processing files and are included to simplify possible reprocessing of the data using the RVDAS NBP processing scripts. All decimal points are implied. Leading zeros and blanks are equivalent. Unknown or unused fields are filled with 9's. All "corrections", such as time zone, diurnal magnetics, and EOTVOS, are understood to be added. Col Len Type Contents Description, Possible Values, Notes 1 1 Int Data record type Set to "5" for data record 2-9 8 Char Survey identifier 10-12 3 int Time zone correction Corrects time (in characters 13-27) to GMT when added; 0 = GMT 13-16 4 int Year 4 digit year 17-18 2 int Month 2 digit month 19-20 2 int Day 21-22 2 int Hour 23-27 5 real Minutes x 1000 28-35 8 real Latitude x 100000 + = North - = South. (-9000000 to 9000000) 36-44 9 real Longitude x 100000 + = East - = West. (-18000000 to 18000000) 45 1 int Position type code 1=Observed fix 3=Interpolated 9=Unspecified 46-51 6 real Bathymetry, 2- way travel time In 10,000th of seconds. Corrected for transducer depth and other such corrections 52-57 6 real Bathymetry, corrected depth In tenths of meters. 58-59 2 int Bathymetric correction code This code details the procedure used for determining the sound velocity correction to depth. 60 1 int Bathymetric type code 1 = Observed 3 = Interpolated (Header Seq. 12) 9 = Unspecified 61-66 6 real Magnetics total field, 1ST sensor In tenths of nanoteslas (gammas) 67-72 6 real Magnetics total field, 2ND sensor In tenths of nanoteslas (gammas), for trailing sensor 73-78 6 real Magnetics residual field In tenths of nanoteslas (gammas). The reference field used is in Header Seq. 13. 79 1 int Sensor for residual field 1 = 1st or leading sensor 2 = 2nd or trailing sensor 9 = Unspecified 80-84 5 real Magnetics diurnal correction In tenths of nanoteslas (gammas). (In nanoteslas) if 9-filled (i.e., set to "+9999"), total and residual fields are assumed to be uncorrected; if used, total and residuals are assumed to have been already corrected. 85-90 6 F6.0 Depth or altitude of magnetics sensor (In meters) + = Below sea level 3 = Above sea level 91-97 7 real Observed gravity In 10th of mgals. Corrected for Eotvos, drift, tares 98-103 6 real EOTVOS correction In tenths of mgals. E = 7.5 V cos phi sin alpha + 0.0042 V*V 104-108 5 real Free-air anomaly In tenths of milligals G = observed G = theoretical 109-113 5 char Seismic line number Cross-reference for seismic data 114-119 6 char Seismic shot-point number 120 1 int Quality code for navigation 5=Suspected, by the originating institution 6=Suspected, by the data center 9=No identifiable problem found