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<title>MGD77LIST</title>
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<body bgcolor="#ffffff">
<h1 align=center>MGD77LIST</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#OPTIONS">OPTIONS</a><br>
<a href="#EXAMPLES">EXAMPLES</a><br>
<a href="#RECALCULATED ANOMALIES">RECALCULATED ANOMALIES</a><br>
<a href="#IGRF">IGRF</a><br>
<a href="#IGF">IGF</a><br>
<a href="#CORRECTIONS">CORRECTIONS</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<a href="#REFERENCES">REFERENCES</a><br>
<hr>
<a name="NAME"></a>
<h2>NAME</h2>
<p style="margin-left:11%; margin-top: 1em">mgd77list
− A data-extractor for MGD77[+] files</p>
<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77list</b>
<i>NGDC-ids</i>
<b>−F</b><i>columns</i>[,<i>logic</i>][:<i>bittests</i>]
[
<b>−A</b>[<b>+</b>]<b>c</b>|<b>d</b>|<b>f</b>|<b>m</b>|<b>t</b><i>code</i>
] [ <b>−Cf</b>|<b>g</b>|<b>e</b> ] [
<b>−DA</b>|<b>a</b><i>startdate</i> ] [
<b>−DB</b>|<b>b</b><i>stopdate</i> ] [ <b>−E</b>
] [ <b>−Ga</b><i>startrec</i> ] [
<b>−Gb</b><i>stoprec</i> ] [
<b>−H</b>[<b>i</b>][<i>nrec</i>] ] [
<b>−I</b><i>ignore</i> ] [
<b>−L</b>[<i>corrtable</i>] ] [
<b>−Nd</b>|<b>s</b><i>unit</i> ] [
<b>−Qa</b>|<b>v</b><i>min</i>/<i>max</i> ] [
<b>−R</b><i>west</i>/<i>east</i>/<i>south</i>/<i>north</i>[<b>r</b>]
] [ <b>−Sa</b><i>startdist</i>[unit] ] [
<b>−Sb</b><i>stopdist</i>[unit] ] [
<b>−T</b>[<b>m</b>|<b>e</b>] ] [ <b>−V</b> ] [
<b>−W</b><i>weight</i> ] [
<b>−Z</b><i>+</i>|<b>-</b> ] [
<b>−bo</b>[<b>s</b>|<b>S</b>|<b>d</b>|<b>D</b>[<i>ncol</i>]|<b>c</b>[<i>var1</i><b>/</b><i>...</i>]]
] [ <b>−m</b>[<i>flag</i>] ]</p>
<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77list</b>
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 <b>mgd77info −C</b>, and to
learn how to add your own custom columns, see
<b><A HREF="mgd77manage.html">mgd77manage</A></b>). 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 <b>−W</b>). 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. <i><br>
NGDC-ids</i></p>
<p style="margin-left:22%;">Can be one or more of five
kinds of specifiers: <br>
1) 8-character NGDC IDs, e.g., 01010083, JA010010etc., etc.
<br>
2) 2-character <agency> codes which will return all
cruises from each agency. <br>
3) 4-character <agency><vessel> codes, which
will return all cruises from those vessels. <br>
4) =<list>, where <list> is a table with NGDC
IDs, one per line. <br>
5) If nothing is specified we return all cruises in the data
base. <br>
(See mgd77info <b>−L</b> for agency and vessel codes).
The ".mgd77" or ".nc" extensions will
automatically be appended, if needed (use <b>−I</b> to
ignore certain file types). Cruise files will be looked for
first in the current directory and second in all directories
listed in <b>$MGD77_HOME</b>/mgd77_paths.txt [If
<b>$MGD77_HOME</b> is not set it will default to
<b>$GMT_SHAREDIR</b>/mgd77].</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>−F</b></p> </td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">The required
<i>columns</i> 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
<b><A HREF="gmtdefaults.html#D_FORMAT">D_FORMAT</A></b>. The available abbreviations are:</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>drt</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">The digital record
type, usually 3 or 5 (for Y2K-compliant cruises).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>id</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">The survey ID
string (leg name).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>ngdcid</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">The 8-character
NGDC cruise ID string (usually the file prefix).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>time</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Choose between
Absolute calendar time (<b>atime</b>, the default) in the
format dictated by the GMT parameters
<b><A HREF="gmtdefaults.html#OUTPUT_DATE_FORMAT">OUTPUT_DATE_FORMAT</A></b> and <b><A HREF="gmtdefaults.html#OUTPUT_CLOCK_FORMAT">OUTPUT_CLOCK_FORMAT</A></b>,
Relative time (<b>rtime</b>) in the format dictated by the
GMT parameters <b><A HREF="gmtdefaults.html#D_FORMAT">D_FORMAT</A></b> and <b><A HREF="gmtdefaults.html#TIME_SYSTEM">TIME_SYSTEM</A></b> (or
<b><A HREF="gmtdefaults.html#TIME_EPOCH">TIME_EPOCH</A></b> and <b><A HREF="gmtdefaults.html#TIME_UNIT">TIME_UNIT</A></b>)), or Fractional year
(<b>ytime</b>) in the format dictated by
<b><A HREF="gmtdefaults.html#D_FORMAT">D_FORMAT</A></b>.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>lon</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Longitude in the
format dictated by the GMT parameter
<b><A HREF="gmtdefaults.html#OUTPUT_DEGREE_FORMAT">OUTPUT_DEGREE_FORMAT</A></b>.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>lat</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Longitude in the
format dictated by the GMT parameter
<b><A HREF="gmtdefaults.html#OUTPUT_DEGREE_FORMAT">OUTPUT_DEGREE_FORMAT</A></b>.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>twt</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Two-Way Travel time
(in s).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>depth</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Corrected
bathymetry (in m, positive below sealevel).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>mtf1</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Magnetic Total
Field intensity from sensor 1 (in nTesla).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>mtf2</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Magnetic Total
Field intensity from sensor 2 (in nTesla).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>mag</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Residual magnetic
anomaly (in nTesla).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>gobs</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Observed gravity
(in mGal).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>faa</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Free-air gravity
anomaly (in mGal).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>ptc</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Position Type Code
(1 = fix, 3 = interpolated, 9 = unspecified).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>bcc</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>btc</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Bathymetric Type
Code, indicating how the bathymetry value was obtained (1 =
observed, 3 = interpolated, 9 = unspecified).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>msens</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Magnetic sensor for
used to evaluate the residual field (1 = 1st or leading
sensor, 2 = 2nd or trailing sensor, 9 = unspecified).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>msd</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Depth (or altitude)
of the magnetic sensor (in m, positive below sealevel).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>diur</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Magnetic diurnal
correction (in nTesla).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>eot</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Eotvos correction
(in mGal).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>sln</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Seismic Line Number
string.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>sspn</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Seismic Shot Point
Number string.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>nqc</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Navigation Quality
Code (5 = suspected, by source institution, 6 = suspected,
by NGDC, 9 = no problems identified).</p></td>
</table>
<p style="margin-left:22%; margin-top: 1em">In addition,
the following derived quantities can be requested:</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>year</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">The year of each
record.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>month</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">The month of each
record.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>day</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">The day of the
month of each record.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>hour</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">The hour of each
record.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>min</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">The minutes of each
record.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>sec</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">The decimal seconds
of each record.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>dist</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Along-track
distance from start of leg. For method of calculation, see
<b>−C</b> [spherical great circle distances], and for
distance units, see <b>−N</b> [km].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>az</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Ship azimuth
(heading) measured clockwise from north (in degrees).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>vel</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Ship speed; see
<b>−N</b> for units [m/s].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>weight</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Weight assigned to
this data set (see <b>−W</b>).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>carter</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Carter depth
correction, if <b>twt</b> is present in file (in m). Sign:
Correction is to be subtracted from uncorrected depths to
yield a corrected depth.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>igrf</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">International
geomagnetic reference field (total field) (in nTesla).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>ngrav</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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
<b>−Af</b> (see that option for more details).</p></td>
</table>
<p style="margin-left:22%; margin-top: 1em">The following
short-hand flags are also recognized:</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="7%">
<p style="margin-top: 1em" valign="top"><b>all</b></p></td>
<td width="4%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">This returns all
data columns in the file.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="7%">
<p style="margin-top: 1em" valign="top"><b>mgd77</b></p></td>
<td width="4%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">This results in all
27 MGD77 fields being written out in the offical MGD77
order.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="7%">
<p style="margin-top: 1em" valign="top"><b>geo</b></p></td>
<td width="4%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">This limits the
output to 10 fields (<b>time</b>, <b>lon</b>, <b>lat</b>
plus the seven geophysical observations <b>twt</b>,
<b>depth</b>, <b>mtf1</b>, <b>mtf2</b>, <b>mag</b>,
<b>gobs</b>, and <b>faa</b>). By appending <b>+</b> to
either of these set we will also append <b>dist</b>,
<b>azim</b>, <b>vel</b>, and <b>weight</b> as listed
above.</p> </td>
</table>
<p style="margin-left:22%; margin-top: 1em">As an option,
logical tests may be added for any of the observations by
appending ,<i>logic</i>, which is itself composed of one or
more comma-separated instructions of the form
<i>par</i><b>OP</b><i>value</i>, where <i>par</i> is one of
the parameters listed above, <b>OP</b> is a logical operator
(<, <=, =, !=, >=, >, |), and <i>value</i> 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 <i>value</i> must be turned on in <i>par</i>. 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
<i>columns</i> 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
<b>−F</b>.</p>
<p style="margin-left:22%; margin-top: 1em">Finally, for
MGD77+ files you may optionally append :<i>bittests</i>
which is : (a colon) followed by one or more comma-separated
+-<i>col</i> 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 <b>MGD77_flags</b> 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).</p>
<a name="OPTIONS"></a>
<h2>OPTIONS</h2>
<p style="margin-left:11%; margin-top: 1em">No space
between the option flag and the associated arguments.</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−A</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">By default,
corrected depth (<b>depth</b>), magnetic residual anomaly
(<b>mag</b>), free-air gravity anomaly (<b>faa</b>), and the
derived quantity Carter depth correction (<b>carter</b>) are
all output as is (if selected in <b>−F</b>); this
option adjusts that behavior. For each of these columns
there are 2−4 ways to adjust the data. Append
<b>c</b>(arter), <b>d</b>(epth), <b>f</b>(aa), or
<b>m</b>(ag) and select the <i>code</i> for the procedure
you want applied. You may select more than one procedure for
a data column by summing their numerical <i>code</i>s (1, 2,
4, and 8). E.g., <b>−Ac</b>3 will first try method
<b>−Ac</b>1 to estimate a Carter correction but if
<b>depth</b> is NaN we will next try <b>−Ac</b>2 which
only uses <b>twt</b>. 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 <b>−A+</b> to recalculate anomalies even
if the anomaly in the file is NaN. Additionally, you can use
<b>−At</b> to create fake times for cruises that has
no time; these are based on distances and cruise
duration.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Ac</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Determines how the
<b>carter</b> correction term is calculated. Below,
C(<b>twt</b>) stands for the Carter-corrected depth (it also
depends on <b>lon</b>, <b>lat</b>), U(<b>twt</b>, <i>v</i>)
is the uncorrected depth (= <b>twt</b> * <i>v</i> / 2) using
as <i>v</i> 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 <i>v</i> in m/s, TU(<b>depth</b>, <i>v</i>) is the
2-way travel time estimated from the (presumably)
uncorrected <b>depth</b>, and TC(<b>depth</b>) is the 2-way
travel time obtained by inverting the (presumably) corrected
<b>depth</b> using the Carter correction formula. Select
from</p> </td>
</table>
<p style="margin-left:22%;"><b>−Ac1</b>[,<i>v</i>]
returns difference between U(<b>twt</b>, <i>v</i>) and
<b>depth</b> [Default]. <b><br>
−Ac2</b>[,<i>v</i>] returns difference between
U(<b>twt</b>, <i>v</i>) and Carter (<b>twt</b>). <b><br>
−Ac4</b>[,<i>v</i>] returns difference between
(assumed uncorrected) <b>depth</b> and Carter
(TU(<b>depth</b>)). <b><br>
−Ac8</b>[,<i>v</i>] returns difference between
U(TC(<b>depth</b>), <i>v</i>) and <b>depth</b>.</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Ad</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Determines how the
<b>depth</b> column output is obtained:</p></td>
<td width="0%">
</td>
</table>
<p style="margin-left:22%;"><b>−Ad1</b> returns
<b>depth</b> as stored in the data set [Default]. <b><br>
−Ad2</b>[,<i>v</i>] returns calculated uncorrected
depth U(<b>twt</b>, <i>v</i>). <b><br>
−Ad4</b> returns calculated corrected depth
C(<b>twt</b>).</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Af</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Determines how the
<b>faa</b> column output is obtained. If <b>ngrav</b> (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
<i>field</i> (1−4) to select 1 (Heiskanen 1924), 2
(IGF 1930), 3 (IGF 1967) or 4 (IGF 1980). Select from</p></td>
</table>
<p style="margin-left:22%;"><b>−Af1</b>[,<i>field</i>]
returns <b>faa</b> as stored in the data set [Default].
Optionally, sets the IGF <i>field</i> to use if you also
have requested <b>ngrav</b> as an output column in
<b>−F</b>. <b><br>
−Af2</b>[,<i>field</i>] returns the difference between
<b>gobs</b> and <b>ngrav</b> (with optional <i>field</i>
directive). <b><br>
−Af3</b>[,<i>field</i>] returns the combination of
<b>gobs</b> + <b>eot</b> - <b>ngrav</b> (with optional
<i>field</i> directive).</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Am</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Determines how the
<b>mag</b> column output is obtained. There may be one or
two total field measurements in the file (<b>mtf1</b> and
<b>mtf2</b>), and the column <b>msens</b> may state which
one is the leading sensor (1 or 2; it may also be
undefined). Select from</p></td>
</table>
<p style="margin-left:22%;"><b>−Am1</b> returns
<b>mag</b> as stored in the data set [Default]. <b><br>
−Am2</b> returns the difference between <b>mgfx</b>
and <b>igrf</b>, where <b>x</b> is the leading sensor
(<b>1</b> or <b>2</b>) indicated by the <b>msens</b> data
field (defaults to <b>1</b> if unspecified). <b><br>
−Am4</b> returns the difference between <b>mgfx</b>
and <b>igrf</b>, where <b>x</b> is the sensor (<b>2</b> or
<b>1</b>) <i>not</i> indicated by the <b>msens</b> data
field (defaults to <b>2</b> if unspecified).</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−C</b></p> </td>
<td width="4%"></td>
<td width="82%">
<p style="margin-top: 1em" valign="top">Append a one-letter
code to select the procedure for along-track distance
calculation (see <b>−N</b> for selecting units):</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%"></td>
<td width="4%"></td>
<td width="82%">
<p valign="top"><b>f</b> Flat Earth distances.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%"></td>
<td width="4%"></td>
<td width="82%">
<p valign="top"><b>g</b> Great circle distances
[Default].</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%"></td>
<td width="4%"></td>
<td width="82%">
<p valign="top"><b>e</b> Geodesic distances on current GMT
ellipsoid.</p> </td>
</table>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Da</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Do not list data
collected before <i>startdate</i>
(yyyy-mm-dd<b>T</b>[hh:mm:ss]) [Default is start of cruise].
Use <b>−DA</b> to exclude records whose time is
undefined (i.e., NaN). [Default reports those records].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Db</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Do not list data
collected on or after <i>stopdate</i>
(yyyy-mm-dd<b>T</b>[hh:mm:ss]). [Default is end of cruise].
Use <b>−DB</b> to exclude records whose time is
undefined (i.e., NaN). [Default reports those records].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−E</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Exact match: Only
output records that match all the requested geophysical
columns [Default outputs records that matches at least one
of the observed columns].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Ga</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Do not list records
before <i>startrec</i> [Default is 0, the first record].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Gb</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Do not list data
after <i>stoprec</i>. [Default is the last record].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−H</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Issue a header
record with names for each data field.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−I</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Ignore certain data
file formats from consideration. Append <b>a|c|t</b> to
ignore MGD77 ASCII, MGD77+ netCDF, or plain tab-separated
ASCII table files, respectively. The option may be repeated
to ignore more than one format. [Default ignores none].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−L</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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
<b>$MGD77_HOME</b> directory]. For the format of this file,
see CORRECTIONS below.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−n</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Issue a
multi-segment header record with cruise ID for each
cruise.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−N</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Append <b>d</b> for
distance or <b>s</b> for speed, then give the desired
<i>unit</i> as <b>e</b> (meter or m/s), <b>k</b> (km or
km/hr), <b>m</b> (miles or miles/hr), or <b>n</b> (nautical
miles or knots). [Default is <b>−Ndk −Nse</b>
(km and m/s)].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Qa</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Specify an accepted
range (<i>min</i>/<i>max</i>) of azimuths. Records whose
track azimuth falls outside this range are ignored
[0-360].</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Qv</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Specify an accepted
range (<i>min</i>/<i>max</i>; or just <i>min</i> if there is
no upper limit) of velocities. Records whose track speed
falls outside this range are ignored [0-infinity].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−R</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top"><i>west, east,
south,</i> and <i>north</i> 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 <b>r</b> if lower
left and upper right map coordinates are given instead of
w/e/s/n. The two shorthands <b>−Rg</b> and
<b>−Rd</b> 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 <b>−R</b> settings (and grid
spacing, if applicable) are copied from the grid.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Sa</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Do not list data
that are less than <i>startdist</i> meter along track from
port of departure. Append <b>k</b> for km, <b>m</b> for
miles, or <b>n</b> for nautical miles [Default is 0
meters].</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Sb</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Do not list data
that are <i>stopdist</i> or more meters along track from
port of departure. Append <b>k</b> for km, <b>m</b> for
miles, or <b>n</b> for nautical miles [Default is end of
track].</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−T</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">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 <b>m</b> or <b>e</b> to limit the
option to the MGD77 or extended columns set only [Default
applies to both].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−V</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Selects verbose
mode, which will send progress reports to stderr [Default
runs "silently"].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−W</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Set the weight for
these data. Weight output option must be set in
<b>−F</b>. This is useful if the data are to be
processed with the weighted averaging techniques offered by
<b><A HREF="blockmean.html">blockmean</A></b>, <b><A HREF="blockmedian.html">blockmedian</A></b>, and <b><A HREF="blockmode.html">blockmode</A></b>
[1].</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Z</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Append the sign you
want for <b>depth</b>, <b>carter</b>, and <b>msd</b> values
below sea level (<b>−Z-</b> gives negative bathymetry)
[Default is positive down].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−bo</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Selects binary
output mode (single precision; append <b>d</b> for double
precision, or use <b>S</b>|<b>D</b> to swap bytes on output)
[Default is ASCII]. <b>−H</b> is ignored if
<b>−bo</b> 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.</p></td>
</table>
<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>
<p style="margin-left:11%; margin-top: 1em">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:</p>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77list</b>
01010047 <b>−Da</b>1971-06-03T20:45
<b>−Sb</b>5000 <b>−F</b>dist,azim,faa,depth >
myfile.d</p>
<p style="margin-left:11%; margin-top: 1em">To make input
for <b><A HREF="blockmean.html">blockmean</A></b> and <b><A HREF="surface.html">surface</A></b> 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:</p>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77list</b>
‘cat cruises.lis‘ <b>−F</b>lon,lat,faa
<b>−R</b>-40/-30/25/35 <b>−bo</b> >
allgrav.b</p>
<p style="margin-left:11%; margin-top: 1em">To extract the
locations of depths exceeding 9000 meter that were not
interpolated (<b>btc</b> != 1) from all the cruises listed
in the file cruises.lis:</p>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77list</b>
‘cat cruises.lis‘
<b>−F</b>"depth,DEPTH>9000,BTC!=1" >
really_deep.d</p>
<p style="margin-left:11%; margin-top: 1em">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</p>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77list</b>
‘cat cruises.lis‘ <b>−E −Ia
−F</b>"dist,faa,grav12_2,depth<3000" >
shallow_grav.d</p>
<p style="margin-left:11%; margin-top: 1em">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</p>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77list</b>
‘cat cruises.lis‘ <b>−E −Ia
−F</b>"dist,faa,grav12_2:+faa" >
bad_grav.d</p>
<p style="margin-left:11%; margin-top: 1em">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:</p>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77list</b>
‘cat cruises.lis‘ <b>−F</b>lon,lat,mag,faa
<b>−Af</b>2,4 <b>−Am</b>2 > data.d</p>
<a name="RECALCULATED ANOMALIES"></a>
<h2>RECALCULATED ANOMALIES</h2>
<p style="margin-left:11%; margin-top: 1em">When
recalculated anomalies are requested (either explicitly via
the <b>−A</b> 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.</p>
<a name="IGRF"></a>
<h2>IGRF</h2>
<p style="margin-left:11%; margin-top: 1em">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.</p>
<a name="IGF"></a>
<h2>IGF</h2>
<p style="margin-left:11%; margin-top: 1em">The equations
used are reproduced here using coefficients extracted
directly from the source code (let us know if you find
errors): <br>
(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)] <br>
(2) g = 978049.0 * [1 + 0.0052884 * sin^2(lat) - 0.0000059 *
sin^2(2*lat)] <br>
(3) g = 978031.846 * [1 + 0.0053024 * sin^2(lat) - 0.0000058
* sin^2(2*lat)] <br>
(4) g = 978032.67714 * [(1 + 0.00193185138639 * sin^2(lat))
/ sqrt (1 - 0.00669437999013 * sin^2(lat))]</p>
<a name="CORRECTIONS"></a>
<h2>CORRECTIONS</h2>
<p style="margin-left:11%; margin-top: 1em">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</p>
<p style="margin-left:11%; margin-top: 1em"><i>cruiseID
observation correction</i></p>
<p style="margin-left:11%; margin-top: 1em">where
<i>cruiseID</i> is a NGDC prefix, <i>observation</i> is one
of the abbreviations for geophysical observations listed
under <b>−F</b> above, and <i>correction</i> consists
of one or more <i>term</i>s that will be summed up and then
<b>subtracted</b> from the observation before output. Each
<i>term</i> must have this exact syntax:</p>
<p style="margin-left:11%; margin-top: 1em"><i>factor</i>[*[<i>function</i>]([<i>scale</i>](<i>abbrev</i>[-<i>origin</i>]))[^<i>power</i>]]</p>
<p style="margin-left:11%; margin-top: 1em">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 <i>term</i>s. The
<i>factor</i> is the amplitude of the basis function, while
the optional <i>function</i> can be one of sin, cos, or exp.
The optional <i>scale</i> and <i>origin</i> can be used to
translate the argument (before giving it to the optional
function). The argument <i>abbrev</i> is one of the
abbreviations for observations listed above. If
<i>origin</i> is given as <b>T</b> it means that we should
replace it with the value of <i>abbrev</i> for the very
first record in the file (this is usually only done for
<i>time</i>). If the first record entry is NaN we revert
<i>origin</i> to zero. Optionally, raise the entire
expression to the given <i>power</i>, before multiplying by
the amplitude. The following is an example of fictitious
corrections to the cruise 99999999, implying the
<b>depth</b> should have the Carter correction removed,
<b>faa</b> should have a linear trend removed, the magnetic
anomaly (<b>mag</b>) should be corrected by a strange
dependency on ship heading and latitude, and <b>gob</b>s
needs to have 10 mGal added (hence given as -10):</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%">
<p valign="top">99999999 depth</p></td>
<td width="15%"></td>
<td width="8%"></td>
<td width="7%">
<p valign="top">1.0*((carter))</p></td>
<td width="24%"></td>
<td width="7%"></td>
<td width="31%">
</td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%">
<p valign="top">99999999 faa</p></td>
<td width="15%"></td>
<td width="8%"></td>
<td width="7%">
<p valign="top">14.1</p></td>
<td width="24%"></td>
<td width="7%"></td>
<td width="31%">
</td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%"></td>
<td width="15%"></td>
<td width="8%"></td>
<td width="7%">
<p valign="top">1e-5*((time-T))</p></td>
<td width="24%"></td>
<td width="7%"></td>
<td width="31%">
</td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%">
<p valign="top">99999999 mag</p></td>
<td width="15%"></td>
<td width="8%"></td>
<td width="7%">
<p valign="top">0.5*cos(0.5*(azim-19))^2</p></td>
<td width="24%"></td>
<td width="7%"></td>
<td width="31%">
<p valign="top">1.0*exp(-1e-3(lat))^1.5</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="-3%">
<p valign="top">99999999 gobs</p></td>
<td width="15%"></td>
<td width="8%"></td>
<td width="7%">
<p valign="top">-10</p></td>
<td width="24%"></td>
<td width="7%"></td>
<td width="31%">
</td>
</table>
<a name="SEE ALSO"></a>
<h2>SEE ALSO</h2>
<p style="margin-left:11%; margin-top: 1em"><i><A HREF="mgd77convert.html">mgd77convert</A></i>(1),
<i><A HREF="mgd77info.html">mgd77info</A></i>(1), <i><A HREF="mgd77manage.html">mgd77manage</A></i>(1),
<i><A HREF="mgd77track.html">mgd77track</A></i>(1)</p>
<a name="REFERENCES"></a>
<h2>REFERENCES</h2>
<p style="margin-left:11%; margin-top: 1em">Wessel, P., and
W. H. F. Smith, 2009, The Generic Mapping Tools (GMT)
version 4.5.0 Technical Reference & Cookbook,
SOEST/NOAA. <br>
Wessel, P., and W. H. F. Smith, 1998, New, Improved Version
of Generic Mapping Tools Released, EOS Trans., AGU, 79 (47),
p. 579. <br>
Wessel, P., and W. H. F. Smith, 1995, New Version of the
Generic Mapping Tools Released, EOS Trans., AGU, 76 (33), p.
329. <br>
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. <br>
Wessel, P., and W. H. F. Smith, 1991, Free Software Helps
Map and Display Data, EOS Trans., AGU, 72 (41), p. 441. <br>
The Marine Geophysical Data Exchange Format -
"MGD77", see
<i>http://www.ngdc.noaa.gov/mgg/dat/geodas/docs/mgd77.txt</i>
<br>
IGRF, see
<i>http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html</i></p>
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