grdgravmag3d
grdgravmag3d - Compute the gravity effect of a grid by the method of Okabe
Synopsis
grdgravmag3d [ -Cdensity ] [ -D ] [ -Fxy_file ]
[ -Goutputgrid.nc ] [ -Lz_observation ] [ -M ]
-V[level]
[ -Zlevel ]
[ -V[level] ]
[ -fg ]
Note: No space is allowed between the option flag and the associated arguments.
Description
grdgravmag3d will compute the gravity anomaly of a body described by
one or (optionally) two grids The output can either be along a given set
of xy locations or on a grid. This method is not particularly fast but
allows computing the anomaly of arbitrarily complex shapes.
Required Arguments
- -Cdensity
- Sets body density in SI. This option is mutually exclusive with
-H.
- -Fxy_file
- Provide locations where the anomaly will be computed. Note this
option is mutually exlusive with -G.
- -Goutgrid.nc
- Output the gravity anomaly at nodes of this grid file.
- -R[unit]xmin/xmax/ymin/ymax[r] (more ...)
- Specify the region of interest.
Optional Arguments
- -V[level] (more ...)
- Select verbosity level [c].
- -L
- sets level of observation [Default = 0]. That is the height (z) at
which anomalies are computed.
- -Z
- level of reference plane [Default = 0]. Use this option when the
triangles describe a non-closed surface and the volume is deffined
from each triangle and this reference level. An example will be the
whater depth to compute a Bouguer anomaly.
- -fg
- Geographic grids (dimensions of longitude, latitude) will be converted to
meters via a “Flat Earth” approximation using the current ellipsoid parameters.
- -^
- Print a short message about the syntax of the command, then exits. (NOTE: on Windows use just -)
- +
- Print an extensive usage (help) message, including the explanation of
any module-specific option (but not the GMT common options), then exits
- -?
- Print a complete usage (help) message, including the explanation of
options, then exits.
- --version
- Print GMT version and exit.
- --show-datadir
- Print full path to GMT share directory and exit.
Grid Distance Units
If the grid does not have meter as the horizontal unit, append +uunit to the input file name to convert from the
specified unit to meter. If your grid is geographic, convert distances to meters by supplying -fg instead.
Examples
Suppose you want to compute the gravity effect of the phantom “Sandy
Island” together with its not phantom seamount
gmt grdgravmag3d sandy_bat.grd -C1700 -Z-4300 -M -I1m -Gsandy_okb.grd -V
Reference
Okabe, M., Analytical expressions for gravity anomalies due to
polyhedral bodies and translation into magnetic anomalies, Geophysics,
44, (1979), p 730-741.