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NAME

       mgd77list - Extract data from 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 ] [  -Iignore ]
       [   -L[corrtable] ] [  -Nd|sunit ] [  -Qa|c|vmin/max ] [  -Rregion ] [  -Sastartdist[unit]
       ] [  -Sbstopdist[unit] ] [  -T[m|e] ] [  -V[level] ] [  -Wweight ] [  -Z+|- ] [  -bobinary
       ] [ -hheaders ]

       Note: No space is allowed between the option flag and the associated arguments.

DESCRIPTION

       mgd77list  reads  MGD77  files  and  produces  an ASCII [or binary] table. The MGD77 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  8  computed  quantities (distance, heading, course-change, velocity,
       Carter correction, Eotvos 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. If multiple cruises are requested then they are separated by segment headers.

REQUIRED ARGUMENTS

       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). If no file extension is given  then
              we  search  for files with one of the four known extensions.  The search order (and
              the extensions) tried is MGD77+ (".nc"), MGD77T (".m77t"), MGD77  (".mgd77"  )  and
              plain  text  file  (".dat").   Use  -I  to ignore one or more of these 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].

       -Fcolumns[,logic][:bittests]
              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 FORMAT_FLOAT_OUT.  The
              available column abbreviations for information stored in the  files  (some  columns
              may be NaN) are:

              recno  The record number counter.

              drt    The digital record type, usually 3 or 5 (for Y2K-compliant cruises).

              id     The survey ID string (leg name).

              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  FORMAT_DATE_OUT  and   FORMAT_CLOCK_OUT,
                     Relative  time  (rtime)  in  the  format  dictated  by  the  GMT  parameters
                     FORMAT_FLOAT_OUT  and  TIME_SYSTEM  (or  TIME_EPOCH  and   TIME_UNIT)),   or
                     Fractional year (ytime) in the format dictated by FORMAT_FLOAT_OUT.

              lon    Longitude in the format dictated by the GMT parameter FORMAT_GEO_OUT.

              lat    Longitude in the format dictated by the GMT parameter FORMAT_GEO_OUT.

              twt    Two-Way Travel time (in s).

              depth  Corrected bathymetry (in m, positive below sea level).

              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).

              In addition, the following derived navigational 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.

              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).

              cc     Ship course change (change in heading) measured  clockwise  from  north  (in
                     degrees).

              vel    Ship speed; see -N for units [m/s].

              Finally, the following computed quantities can be requested:

              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 added to 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).

              ceot   Calculated Eotvos correction from  navigation,  using  E  =  7.5038  *  V  *
                     cos(lat)  *  sin(az)  +  0.004154 * V^2 (in mGal). Sign: Correction is to be
                     added to uncorrected faa to yield a corrected faa.

              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 The full set of all 26 columns in the MGD77T specification.

              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, cc, vel,
                     and weight as listed above.

              all    This returns all data columns in the file.

              allt   As mgd77t but with time items written as a date-time string.

              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.
              Notes:  (1)  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. (2)
              Some  of  the  operators  are  special UNIX characters and you are advised to place
              quotes around the entire argument to -F.  (3)  The  logical  tests  only  apply  to
              observed  data;  derived data (such as distances, velocities, etc.) must be limited
              using program options such as -D, -Q, -S, etc.

              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).  Note that these record-based flags are different
              from any systematic corrections along track; the latter are deactivated by -T.

OPTIONAL ARGUMENTS

       -A[+]c|d|f|m|tcode
              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., -Ac3 will first try method -Ac1 to estimate a  Carter
              correction  but  if  depth is NaN we will next try -Ac2 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).

              -Af4[,field]  returns  the  combination  of gobs + eot - ngrav (with optional field
              directive).

              -Af8[,field] returns the combination of gobs +  pred_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).

              -Amcoffset[unit]  applies a correction to compensate for the fact that the magnetic
              field was not acquired at the same position  as  the  ship's  position  [i.e.,  the
              navigation].  This  is accomplished by re-interpolating the total magnetic field to
              what it would have been if it were measured at the ship's  position  (remember,  it
              probably  was  measured  offset meters behind). Due to this interpolation step, bad
              navigation, namely too many repeated points, may cause trouble.  Measures are taken
              to  minimize  this effect but they aren't 100% fool proof. The interpolation method
              is controlled by the GMT default GMT_INTERPOLANT. Append e for meter, f for feet, k
              for  km,  M  for  miles,  n  for nautical miles, or u for survey feet [Default is e
              (meters)].

       -Cf|g|e
              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.

       -Dastartdate
              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].

       -Dbstopdate
              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].

       -Gastartrec
              Do not list records before startrec [Default is 0, the first record].

       -Gbstoprec
              Do not list data after stoprec. [Default is the last record].

       -Iignore
              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[corrtable]
              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     Issue a segment header record with cruise ID for each cruise.

       -Nd|sunit
              Append d for distance or s for speed, then give the desired unit  as  e  (meter  or
              m/s), f (feet or feet/s), k (km or km/hr), m (miles or miles/hr), n (nautical miles
              or knots), or u (survey feet or sfeet/s). [Default is -Ndk -Nse (km and m/s)].

       -Qamin/max
              Specify an accepted range (min/max) of azimuths. Records whose track azimuth  falls
              outside this range are ignored [0/360].

       -Qcmin/max
              Specify  an  accepted range (min/max) of course changes. Records whose track course
              change falls outside this range are  ignored  [-360/+360].  Use  -QC  to  take  the
              absolute  value  of  the  course change before the test [Default uses signed course
              changes].

       -Qvmin/max
              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].

       -Rwest/east/south/north[/zmin/zmax][+r][+uunit]
              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  for  grid  creation,  give
              Rcodelon/lat/nx/ny,  where  code is a 2-character combination of L, C, R (for left,
              center, or right) and T, M, B for top, middle, or bottom. e.g., BL for lower  left.
              This  indicates  which  point on a rectangular region the lon/lat coordinate refers
              to, and the grid dimensions nx and ny with grid spacings via -I is used  to  create
              the corresponding region.  Alternatively, specify the name of an existing grid file
              and the -R settings (and grid spacing, if applicable) are  copied  from  the  grid.
              Appending  +uunit  expects projected (Cartesian) coordinates compatible with chosen
              -J and we inversely project to determine actual rectangular geographic region.  For
              perspective  view  (-p), optionally append /zmin/zmax.  In case of perspective view
              (-p), a z-range (zmin, zmax) can be appended to indicate the third dimension.  This
              needs to be done only when using the -Jz option, not when using only the -p option.
              In the latter case a perspective view of  the  plane  is  plotted,  with  no  third
              dimension.

       -Sastartdist[unit]
              Do  not  list  data  that  are  less  than startdist meter along track from port of
              departure. Append e for meter, f for feet, k for km, m for miles,  n  for  nautical
              miles, or u for survey feet [Default is 0e (meters)].

       -Sbstopdist[unit]
              Do  not  list  data  that  are  stopdist  or  more  meters along track from port of
              departure. Append e for meter, f for feet, k for km, m for miles,  n  for  nautical
              miles, or u for survey feet [Default is end of track].

       -T[m|e]
              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].  Note that record-based E77  flags  (MGD77+  format
              only) are not considered systematic corrections.  Instead, the application of these
              bit-flags can be controlled via the : (colon) modifier to OPT(F).

       -V[level] (more ...)
              Select verbosity level [c].

       -Wweight
              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[ncols][type] (more ...)
              Select  native  binary  output. 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=1.

       -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
              Skip or produce header record(s).

       -^ or just -
              Print a short message about the syntax of the command, then exits (NOTE: on Windows
              just use -).

       -+ or just +
              Print  an  extensive  usage  (help)  message,  including  the  explanation  of  any
              module-specific option (but not the GMT common options), then exits.

       -? or no arguments
              Print a complete usage (help) message, including the explanation  of  all  options,
              then exits.

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:

              gmt mgd77list 01010047 -Da1971-06-03T20:45 -Sb5000 -Fdist,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:

              gmt mgd77list `cat cruises.lis` -Flon,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:

              gmt 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

              gmt 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

              gmt 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:

              gmt mgd77list `cat cruises.lis` -Flon,lat,mag,faa -Af2,4 -Am2 > 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

SEE ALSO

       blockmean,  blockmedian,  blockmode,  mgd77convert,  mgd77info,  mgd77manage,  mgd77track,
       surface,

REFERENCES

       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/

COPYRIGHT

       2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe