grdgravmag3d

grdgravmag3d(cmd0::String="", arg1=nothing, kwargs...)

Description

Compute the gravity or magnetic 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

grd_top (and optionally grd_bot). Grid(s) whose gravity/mag effect is going to be computed. If two grids are provided then the gravity/magnetic effect of the volume between them is computed.

• C or density : – density=??
  Sets body density in SI. Append either a constant, the name of a grid file or a GMTgrid grid with variable densities. This option is mutually exclusive with mag_params

• F or track : – track=xy_loc
  Provide xy_loc (file name or GMTdataset) locations where the anomaly will be computed. Note, this option is mutually exclusive with the save option.

• G or save or outgrid or outfile : – save=file_name.grd
  Write one or more fields directly to grids on disk or return them to the Julia REPL as grid objects. If more than one field is specified via fields then file_name must contain the format flag %s so that we can embed the field code in the file names.

Optional Arguments

• E or thickness : – thickness=??
  To provide the layer thickness in m [Default = 500 m].

• H or mag_params : – magparams=fdec/fdip/mint/mdec/mdip | mag_params="magfile"|maggrid | magparams="x|X|y|Y|z|Z|h|H|t|T|f|F" | *magparams="+i|+n"
  Sets parameters for computation of magnetic anomaly (Can be used multiple times).

  - *f_dec/f_dip* -> geomagnetic declination/inclination
  
  - *m_int/m_dec/m_dip* -> body magnetic intensity/declination/inclination

  OR for a grid mode

  - *maggrid*, a \myreflink{GMTgrid}  grid, or *magfile*, where *magfile* is the name of the magnetic intensity file.

  To compute a component, specify any of:

  - **x**|**X**|**e**|**E**  to compute the E-W component.
  
  - **y**|**Y**|**n**|**N**  to compute the N-S component.
  
  - **z**|**Z**      to compute the Vertical component.
  
  - **h**|**H**      to compute the Horizontal component.
  
  - **t**|**T**|**f**|**F**  to compute the total field.

  If we want to compute the magnetic anomalies over a large region where the ambient magnetic field can no longer be assumed to be constant we can set variable inclinations and declinations via IGRF. Set any of mag_params="+i|+n" to do that.

• I or inc or increment or spacing : – inc=x_inc | inc=(xinc, yinc) | inc="xinc[+e|n][/yinc[+e|n]]"
  Specify the grid increments or the block sizes. More at spacing

• L or level or reference_level : – z_obs=0
  Sets level of observation [Default = 0]. That is the height (z) at which anomalies are computed.

• Q or pad : – pad="nnpad" | *pad="paddist" | pad="region"
  Extend the domain of computation with respect to output region region. - pad="nn_pad" artificially extends the width of the outer rim of cells to have a fake width of n_pad * dx[/dy].

  - *pad="pad_dist"* extend the region by west-pad, east+pad, etc.
  
  - *pad="west/east/south/north"* Same syntax as **region**.

• R or region or limits : – limits=(xmin, xmax, ymin, ymax) | limits=(BB=(xmin, xmax, ymin, ymax),) | limits=(LLUR=(xmin, xmax, ymin, ymax),units="unit") | ...more
  Specify the region of interest. More at limits. For perspective view view, optionally add zmin,zmax. This option may be used to indicate the range used for the 3-D axes. You may ask for a larger w/e/s/n region to have more room between the image and the axes.

• S or radius : – radius=30
  Set search radius in km (valid only in the two grids mode OR when thickness) [Default = 30 km]. This option serves to speed up the computation by not computing the effect of prisms that are further away than radius from the current node.

• V or verbose : – verbose=true | verbose=level
  Select verbosity level. More at verbose

• Z or level or reference_level : – level="b|t" | level=(bottom=true | top=true)
  level of reference plane [Default = 0]. Use this option when the triangles describe a non-closed surface and the volume is defined from each triangle and this reference level. An example will be the water depth to compute a Bouguer anomaly. Use level=:b or level=:t to close the body at its bottom (for example, to compute the effect of a dome) or at its top (to compute the effect of a spoon).

• f or colinfo : – colinfo=??
  Specify the data types of input and/or output columns (time or geographical data). More at

• x or cores : – cores=N
  Limit the number of cores used when making the individual frames. By default we try to use all available cores. Append N to only use n cores (if too large it will be truncated to the maximum cores available). Finally, give a negative N to select (all - N) cores (or at least 1 if N equals or exceeds all). The parallel processing does not depend on OpenMP.

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 f=:g instead.

Examples

To compute the vertical component due to a magnetization stored in mag.grd over a zone defined by the surface bat.grd, using variable declination and inclination provided the IGRF and using 4 processors, do:

G = grdgravmag3d("bat.grd", thickness=10000, H="z -H+n -H+mmag.grd", x=4, radius=50);

Suppose you want to compute the gravity effect of the Gorringe bank.

using GMT

G = grdgravmag3d("@earth_relief_10m", region=(-12.5,-10,35.5,37.5),
                 density=2700, inc=0.05, pad=0.5, z_level=:bottom, f=:g);
viz(G, title="Gorringe FAA", colorbar=true)

See Also

gravmag3d, gravprism, talwani2d, talwani3d

Reference

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