Provided by: gmt_4.5.11-1build1_amd64 
NAME
mgd77list - A data-extractor for MGD77[+] files
SYNOPSIS
mgd77list NGDC-ids -Fcolumns[,logic][:bittests] [ -A[+]c|d|f|m|tcode ] [ -Cf|g|e ] [ -DA|astartdate ] [
-DB|bstopdate ] [ -E ] [ -Gastartrec ] [ -Gbstoprec ] [ -H[i][nrec] ] [ -Iignore ] [ -L[corrtable] ] [
-Nd|sunit ] [ -Qa|vmin/max ] [ -Rwest/east/south/north[r] ] [ -Sastartdist[unit] ] [ -Sbstopdist[unit] ]
[ -T[m|e] ] [ -V ] [ -Wweight ] [ -Z+|- ] [ -bo[s|S|d|D[ncol]|c[var1/...]] ] [ -m[flag] ]
DESCRIPTION
mgd77list reads <NGDC-id>.[mgd77|nc] files and produces an ASCII [or binary] table. The <NGDC-
id>.[mgd77|nc] files contain track information such as leg-id, time and position, geophysical observables
such as gravity, magnetics, and bathymetry, and control codes and corrections such as Eotvos and diurnal
corrections. The MGD77+ extended netCDF files may also contain additional user columns (for a listing of
available columns, use mgd77info -C, and to learn how to add your own custom columns, see mgd77manage).
The user may extract any combination of these parameters, any of six computed quantities (distance,
heading, velocity, Carter correction, and gravity and magnetic global reference fields), calendar sub-
units of time (year, month, day, hour, min, sec), the NGDC id, and finally a preset weight (see -W). A
sub-section can be specified by passing time- or distance-intervals along track or by selecting a
geographical region. Finally, each output record may be required to pass any number of logical tests
involving data values or bit flags.
NGDC-ids
Can be one or more of five kinds of specifiers:
1) 8-character NGDC IDs, e.g., 01010083, JA010010etc., etc.
2) 2-character <agency> codes which will return all cruises from each agency.
3) 4-character <agency><vessel> codes, which will return all cruises from those vessels.
4) =<list>, where <list> is a table with NGDC IDs, one per line.
5) If nothing is specified we return all cruises in the data base.
(See mgd77info -L for agency and vessel codes). The ".mgd77" or ".nc" extensions will
automatically be appended, if needed (use -I to ignore certain file types). Cruise files will be
looked for first in the current directory and second in all directories listed in
$MGD77_HOME/mgd77_paths.txt [If $MGD77_HOME is not set it will default to $GMT_SHAREDIR/mgd77].
-F The required columns string must be a comma-separated list of parameter abbreviations given in the
desired output order. Any parameters given in UPPER case must not be NaN in a record for output
to occur. Unless specified separately, the output format (if ASCII) is controlled by the GMT
parameter D_FORMAT. The available abbreviations are:
drt The digital record type, usually 3 or 5 (for Y2K-compliant cruises).
id The survey ID string (leg name).
tz The time zone adjustment (in hours from -13 to +12)
ngdcid The 8-character NGDC cruise ID string (usually the file prefix).
time Choose between Absolute calendar time (atime, the default) in the format dictated by the GMT
parameters OUTPUT_DATE_FORMAT and OUTPUT_CLOCK_FORMAT, Relative time (rtime) in the format
dictated by the GMT parameters D_FORMAT and TIME_SYSTEM (or TIME_EPOCH and TIME_UNIT)), or
Fractional year (ytime) in the format dictated by D_FORMAT.
lon Longitude in the format dictated by the GMT parameter OUTPUT_DEGREE_FORMAT.
lat Longitude in the format dictated by the GMT parameter OUTPUT_DEGREE_FORMAT.
twt Two-Way Travel time (in s).
depth Corrected bathymetry (in m, positive below sealevel).
mtf1 Magnetic Total Field intensity from sensor 1 (in nTesla).
mtf2 Magnetic Total Field intensity from sensor 2 (in nTesla).
mag Residual magnetic anomaly (in nTesla).
gobs Observed gravity (in mGal).
faa Free-air gravity anomaly (in mGal).
ptc Position Type Code (1 = fix, 3 = interpolated, 9 = unspecified).
bcc Bathymetric Correction Code, indicating the procedure used to convert travel time to depth.
(01-55 = Matthews' zone used to correct the depth, 59 = Matthews' corrections used but the zones
is unspecified in the data record, 60 = S. Kuwahara formula for T-S, 61 = Wilson formula for T-S,
62 = Del Grosso formula for T-S, 63 = Carter's tables, 88 = Other, described in header sections,
99 = unspecified).
btc Bathymetric Type Code, indicating how the bathymetry value was obtained (1 = observed, 3 =
interpolated, 9 = unspecified).
msens Magnetic sensor for used to evaluate the residual field (1 = 1st or leading sensor, 2 = 2nd or
trailing sensor, 9 = unspecified).
msd Depth (or altitude) of the magnetic sensor (in m, positive below sealevel).
diur Magnetic diurnal correction (in nTesla).
eot Eotvos correction (in mGal).
sln Seismic Line Number string.
sspn Seismic Shot Point Number string.
nqc Navigation Quality Code (5 = suspected, by source institution, 6 = suspected, by NGDC, 9 = no
problems identified).
bqc Bathymetry Quality Code (1 = good, 2 = fair, 3 = poor, 4 = bad, 5 = bad, suspected by source
institution, 6 = bad, suspected by NGDC, 9 = not set).
mqc Magnetics Quality Code (1 = good, 2 = fair, 3 = poor, 4 = bad, 5 = bad, suspected by source
institution, 6 = bad, suspected by NGDC, 9 = not set).
gqc Gravity Quality Code (1 = good, 2 = fair, 3 = poor, 4 = bad, 5 = bad, suspected by source
institution, 6 = bad, suspected by NGDC, 9 = not set).
In addition, the following derived quantities can be requested:
year The year of each record.
month The month of each record.
day The day of the month of each record.
hour The hour of each record.
min The minutes of each record.
sec The decimal seconds of each record.
date The date in yyyymmdd string format.
hhmm The clock in hhmm.xxxx format (0-2359.xxxx).
dmin The decimal minutes of each record (0-59.xxxx).
dist Along-track distance from start of leg. For method of calculation, see -C [spherical great circle
distances], and for distance units, see -N [km].
az Ship azimuth (heading) measured clockwise from north (in degrees).
vel Ship speed; see -N for units [m/s].
weight Weight assigned to this data set (see -W).
carter Carter depth correction, if twt is present in file (in m). Sign: Correction is to be subtracted
from uncorrected depths to yield a corrected depth.
igrf International geomagnetic reference field (total field) (in nTesla).
ngrav International Gravity reference Field ("normal gravity") (in mGal). Field is selected based on
the parameter Gravity Theoretical Formula Code in the cruise's MGD77 header. If this is not set
or is invalid we default to the IGF 1980. Alternatively, specify the field directly using -Af
(see that option for more details).
The following short-hand flags are also recognized:
mgd77 This results in all 27 MGD77 fields being written out in the official MGD77 order.
mgd77t This results in all 26 MGD77T fields being written out in the official MGD77T order.
all as mgd77 or mgd77t but time is written as a single date-time string.
geo This limits the output to 10 fields (time, lon, lat plus the seven geophysical observations twt,
depth, mtf1, mtf2, mag, gobs, and faa). By appending + to either of these set we will also append
dist, azim, vel, and weight as listed above.
As an option, logical tests may be added for any of the observations by appending ,logic, which is
itself composed of one or more comma-separated instructions of the form parOPvalue, where par is
one of the parameters listed above, OP is a logical operator (<, <=, =, !=, >=, >, |), and value
is a constant used in the comparison. Floating point parameters are compared numerically;
character parameters are compared lexically (after leading and trailing blanks have been removed).
The bit comparison (|) means that at least one of the bits in value must be turned on in par. At
least one of the tests must be true for the record to be output, except for tests using UPPER case
parameters which all must be true for output to occur. Note that specifying a test does not imply
that the corresponding column will be included in the output stream; it must be present in columns
for that to occur. Note: some of the operators are special UNIX characters and you are advised to
place quotes around the entire argument to -F.
Finally, for MGD77+ files you may optionally append :bittests which is : (a colon) followed by one
or more comma-separated +-col terms. This compares specific bitflags only for each listed column.
Here, + means the chosen bit must be 1 (ON) whereas - means it must be 0 (OFF). All bit tests
given must be passed. By default, MGD77+ files that have the special MGD77_flags column present
will use those flags, and observations associated with ON-bits (meaning they are flagged as bad)
will be set to NaN; append : with no trailing information to turn this behavior off (i.e., no bit
flags will be consulted).
OPTIONS
No space between the option flag and the associated arguments.
-A By default, corrected depth (depth), magnetic residual anomaly (mag), free-air gravity anomaly
(faa), and the derived quantity Carter depth correction (carter) are all output as is (if selected
in -F); this option adjusts that behavior. For each of these columns there are 2-4 ways to adjust
the data. Append c(arter), d(epth), f(aa), or m(ag) and select the code for the procedure you
want applied. You may select more than one procedure for a data column by summing their numerical
codes (1, 2, 4, and 8). E.g., -Ac 3 will first try method -Ac 1 to estimate a Carter correction
but if depth is NaN we will next try -Ac 2 which only uses twt. In all cases, if any of the
values required by an adjustment procedure is NaN then the result will be NaN. This is also true
if the original anomaly is NaN. Specify -A+ to recalculate anomalies even if the anomaly in the
file is NaN. Additionally, you can use -At to create fake times for cruises that has no time;
these are based on distances and cruise duration.
-Ac Determines how the carter correction term is calculated. Below, C(twt) stands for the Carter-
corrected depth (it also depends on lon, lat), U(twt, v) is the uncorrected depth (= twt * v / 2)
using as v the "Assumed Sound Velocity" parameter in the MGD77 header (if it is a valid velocity,
otherwise we default to 1500 m/s); alternatively, append your preferred velocity v in m/s,
TU(depth, v) is the 2-way travel time estimated from the (presumably) uncorrected depth, and
TC(depth) is the 2-way travel time obtained by inverting the (presumably) corrected depth using
the Carter correction formula. Select from
-Ac1[,v] returns difference between U(twt, v) and depth [Default].
-Ac2[,v] returns difference between U(twt, v) and Carter (twt).
-Ac4[,v] returns difference between (assumed uncorrected) depth and Carter (TU(depth)).
-Ac8[,v] returns difference between U(TC(depth), v) and depth.
-Ad Determines how the depth column output is obtained:
-Ad1 returns depth as stored in the data set [Default].
-Ad2[,v] returns calculated uncorrected depth U(twt, v).
-Ad4 returns calculated corrected depth C(twt).
-Af Determines how the faa column output is obtained. If ngrav (i.e., the International Gravity
reference Field (IGF), or "normal gravity") is required it is selected based on the MGD77 header
parameter "Theoretical Gravity Formula Code"; if this code is not present or is invalid we default
to 4. Alternatively, append the preferred field (1-4) to select 1 (Heiskanen 1924), 2 (IGF 1930),
3 (IGF 1967) or 4 (IGF 1980). Select from
-Af1[,field] returns faa as stored in the data set [Default]. Optionally, sets the IGF field to
use if you also have requested ngrav as an output column in -F.
-Af2[,field] returns the difference between gobs and ngrav (with optional field directive).
-Af3[,field] returns the combination of gobs + eot - ngrav (with optional field directive).
-Am Determines how the mag column output is obtained. There may be one or two total field
measurements in the file (mtf1 and mtf2), and the column msens may state which one is the leading
sensor (1 or 2; it may also be undefined). Select from
-Am1 returns mag as stored in the data set [Default].
-Am2 returns the difference between mgfx and igrf, where x is the leading sensor (1 or 2)
indicated by the msens data field (defaults to 1 if unspecified).
-Am4 returns the difference between mgfx and igrf, where x is the sensor (2 or 1) not indicated by
the msens data field (defaults to 2 if unspecified).
-C Append a one-letter code to select the procedure for along-track distance calculation (see -N for
selecting units):
f Flat Earth distances.
g Great circle distances [Default].
e Geodesic distances on current GMT ellipsoid.
-Da Do not list data collected before startdate (yyyy-mm-ddT[hh:mm:ss]) [Default is start of cruise].
Use -DA to exclude records whose time is undefined (i.e., NaN). [Default reports those records].
-Db Do not list data collected on or after stopdate (yyyy-mm-ddT[hh:mm:ss]). [Default is end of
cruise]. Use -DB to exclude records whose time is undefined (i.e., NaN). [Default reports those
records].
-E Exact match: Only output records that match all the requested geophysical columns [Default outputs
records that matches at least one of the observed columns].
-Ga Do not list records before startrec [Default is 0, the first record].
-Gb Do not list data after stoprec. [Default is the last record].
-H Issue a header record with names for each data field.
-I Ignore certain data file formats from consideration. Append a|c|m|t to ignore MGD77 ASCII, MGD77+
netCDF, MGD77T ASCII or plain tab-separated ASCII table files, respectively. The option may be
repeated to ignore more than one format. [Default ignores none].
-L Apply optimal corrections to columns where such corrections are available. Append the correction
table to use [Default uses the correction table mgd77_corrections.txt in the $MGD77_HOME
directory]. For the format of this file, see CORRECTIONS below.
-N Append d for distance or s for speed, then give the desired unit as e (meter or m/s), k (km or
km/hr), m (miles or miles/hr), or n (nautical miles or knots). [Default is -Ndk -Nse (km and
m/s)].
-Qa Specify an accepted range (min/max) of azimuths. Records whose track azimuth falls outside this
range are ignored [0-360].
-Qv Specify an accepted range (min/max; or just min if there is no upper limit) of velocities.
Records whose track speed falls outside this range are ignored [0-infinity].
-R west, east, south, and north specify the Region of interest, and you may specify them in decimal
degrees or in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left and upper right map
coordinates are given instead of w/e/s/n. The two shorthands -Rg and -Rd stand for global domain
(0/360 and -180/+180 in longitude respectively, with -90/+90 in latitude). Alternatively, specify
the name of an existing grid file and the -R settings (and grid spacing, if applicable) are copied
from the grid.
-Sa Do not list data that are less than startdist meter along track from port of departure. Append k
for km, m for miles, or n for nautical miles [Default is 0 meters].
-Sb Do not list data that are stopdist or more meters along track from port of departure. Append k
for km, m for miles, or n for nautical miles [Default is end of track].
-T Turns OFF the otherwise automatic adjustment of values based on correction terms that are stored
in the MGD77+ file and used to counteract such things as wrong units used by the source
institution when creating the original MGD77 file from which the MGD77+ file derives (the option
has no effect on plain MGD77 ASCII files). Append m or e to limit the option to the MGD77 or
extended columns set only [Default applies to both].
-V Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].
-W Set the weight for these data. Weight output option must be set in -F. This is useful if the
data are to be processed with the weighted averaging techniques offered by blockmean, blockmedian,
and blockmode [1].
-Z Append the sign you want for depth, carter, and msd values below sea level (-Z- gives negative
bathymetry) [Default is positive down].
-bo Selects binary output mode (single precision; append d for double precision, or use S|D to swap
bytes on output) [Default is ASCII]. -H is ignored if -bo is selected. Likewise, string-fields
cannot be selected. Note that if time is one of the binary output columns it will be stored as
Unix-time (seconds since 1970). To read this information in GMT to obtain absolute calendar time
will require you to use --TIME_SYSTEM=unix.
-m[flag]
Issue a multi-segment header record with cruise ID for each cruise.
EXAMPLES
To get a (distance, heading, gravity, bathymetry) listing from 01010047.mgd77, starting at June 3 1971
20:45 and ending at distance = 5000 km, use the following command:
mgd77list 01010047 -Da 1971-06-03T20:45 -Sb 5000 -F dist,azim,faa,depth > myfile.d
To make input for blockmean and surface using free-air anomalies from all the cruises listed in the file
cruises.lis, but only the data that are inside the specified area, and make the output binary:
mgd77list `cat cruises.lis` -F lon,lat,faa -R-40/-30/25/35 -bo > allgrav.b
To extract the locations of depths exceeding 9000 meter that were not interpolated (btc != 1) from all
the cruises listed in the file cruises.lis:
mgd77list `cat cruises.lis` -F"depth,DEPTH>9000,BTC!=1" > really_deep.d
To extract dist, faa, and grav12_2 from records whose depths are shallower than 3 km and where none of
the requested fields are NaN, from all the MGD77+ netCDF files whose cruise ids are listed in the file
cruises.lis, we try
mgd77list `cat cruises.lis` -E -Ia -F"dist,faa,grav12_2,depth<3000" > shallow_grav.d
To extract dist, faa, and grav12_2 from all the MGD77+ netCDF files whose cruise ids are listed in the
file cruises.lis, but only retrieve records whose bitflag for faa indicates BAD values, we try
mgd77list `cat cruises.lis` -E -Ia -F"dist,faa,grav12_2:+faa" > bad_grav.d
To output lon, lat, mag, and faa from all the cruises listed in the file cruises.lis, but recalculate the
two residuals based on the latest reference fields, try:
mgd77list `cat cruises.lis` -F lon,lat,mag,faa -Af 2,4 -Am 2 > data.d
RECALCULATED ANOMALIES
When recalculated anomalies are requested (either explicitly via the -A option or implicitly via E77
metadata in the MGD77+ file) we only do so for the records whose original anomaly was not a NaN. This
restriction is implemented since many anomaly columns contains corrections, usually in the form of hand-
edited changes, that cannot be duplicated from the corresponding observation.
IGRF
The IGRF calculations are based on a Fortran program written by Susan Macmillan, British Geological
Survey, translated to C via f2c by Joaquim Luis, U Algarve, and adapted to GMT-style by Paul Wessel.
IGF
The equations used are reproduced here using coefficients extracted directly from the source code (let us
know if you find errors):
(1) g = 978052.0 * [1 + 0.005285 * sin^2(lat) - 7e-6 * sin^2(2*lat) + 27e-6 * cos^2(lat) * cos^2(lon-18)]
(2) g = 978049.0 * [1 + 0.0052884 * sin^2(lat) - 0.0000059 * sin^2(2*lat)]
(3) g = 978031.846 * [1 + 0.0053024 * sin^2(lat) - 0.0000058 * sin^2(2*lat)]
(4) g = 978032.67714 * [(1 + 0.00193185138639 * sin^2(lat)) / sqrt (1 - 0.00669437999013 * sin^2(lat))]
CORRECTIONS
The correction table is an ASCII file with coefficients and parameters needed to carry out corrections.
Comment records beginning with # are allowed. All correction records are of the form
cruiseID observation correction
where cruiseID is a NGDC prefix, observation is one of the abbreviations for geophysical observations
listed under -F above, and correction consists of one or more terms that will be summed up and then
subtracted from the observation before output. Each term must have this exact syntax:
factor[*[function]([scale](abbrev[-origin]))[^power]]
where terms in brackets are optional (the brackets themselves are not used but regular parentheses must
be used as indicated). No spaces are allowed except between terms. The factor is the amplitude of the
basis function, while the optional function can be one of sin, cos, or exp. The optional scale and origin
can be used to translate the argument (before giving it to the optional function). The argument abbrev
is one of the abbreviations for observations listed above. If origin is given as T it means that we
should replace it with the value of abbrev for the very first record in the file (this is usually only
done for time). If the first record entry is NaN we revert origin to zero. Optionally, raise the entire
expression to the given power, before multiplying by the amplitude. The following is an example of
fictitious corrections to the cruise 99999999, implying the depth should have the Carter correction
removed, faa should have a linear trend removed, the magnetic anomaly (mag) should be corrected by a
strange dependency on ship heading and latitude, and gobs needs to have 10 mGal added (hence given as
-10):
99999999 depth 1.0*((carter))
99999999 faa 14.1 1e-5*((time-T))
99999999 mag 0.5*cos(0.5*(azim-19))^2 1.0*exp(-1e-3(lat))^1.5
99999999 gobs -10
QUALITY CODES
The MGD77T format added three quality codes for bathymetry (bqc), magnetics (mqc), and gravity (gqc).
They are not present in the original MGD77 format, and if requested will return 9 or NULL.
SEE ALSO
mgd77convert(1), mgd77info(1), mgd77manage(1), mgd77track(1)
REFERENCES
Wessel, P., and W. H. F. Smith, 2013, The Generic Mapping Tools (GMT) version 4.5.11 Technical Reference
& Cookbook, SOEST/NOAA.
Wessel, P., and W. H. F. Smith, 1998, New, Improved Version of Generic Mapping Tools Released, EOS
Trans., AGU, 79 (47), p. 579.
Wessel, P., and W. H. F. Smith, 1995, New Version of the Generic Mapping Tools Released, EOS Trans., AGU,
76 (33), p. 329.
Wessel, P., and W. H. F. Smith, 1995, New Version of the Generic Mapping Tools Released,
http://www.agu.org/eos_elec/95154e.html, Copyright 1995 by the American Geophysical Union.
Wessel, P., and W. H. F. Smith, 1991, Free Software Helps Map and Display Data, EOS Trans., AGU, 72 (41),
p. 441.
The Marine Geophysical Data Exchange Format - "MGD77", see
http://www.ngdc.noaa.gov/mgg/dat/geodas/docs/mgd77.txt
IGRF, see http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html