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

See Also

gmt, gmtgravmag3d

Reference

Okabe, M., Analytical expressions for gravity anomalies due to polyhedral bodies and translation into magnetic anomalies, Geophysics, 44, (1979), p 730-741.