NOAA / NESDIS / National Geophysical Data Center / WDC for SEG, Boulder, Colorado USA

Chapter 1: GEOMAGNETISM

Example 1.1

Use the program dir_cart to convert the data in ex1.1 from declination D, inclination I and intensity

All programs respond with help commands to the syntax: % programname -h where the % symbol stands for the command line prompt. So to find out what dir_cart does, type:

% dir_cart -h

to which the computer responds:

Usage: dir_cart [-m] [Standard I/O] options:

-m read magnitude field
input: declination, inclination, [magnitude] or longitude,latitude
output: x1,x2,x3

From this, we see that to convert D,I,M data to cartesian components, we can enter the contents of the file directly :

% dir_cart -m
20 46 1.3 [Input D, I, M]
175 -24 4.2[Output x₁, x₂, x₃]
[ type <control-D> to finish] or:

% dir_cart -m < ex1.1

and the computer responds:

Taking advantage of the UNIX ability to redirect output, the output can be put into a file by:

% dir_cart -m < ex1.1 > ex1.1a

ex1.1a can be printed (with lpr on many systems), listed to the screen (with cat or more), or used as input for another program with the UNIX pipe facility.

Example 1.2

Use the program cart_dir to convert the cartesian coordinates in ex1.1a to geomagnetic elements:

Solution

Type:
% cart_dir
0.3971 -.1445 0.9063 E+01 [Input x₁, x₂, x₃]
-.5722 .0400 -.8192 E+01   [Output D, I, M]
[type <control-D> to finish]

or use cat as in the first example.

Example 1.3

Use the program eqarea to plot an equal area projection of the directions in ex1.3.

Solution Type:

% eqarea < ex1.3 | plotxy

The program plotxy produces Postscript output which can be viewed with ghostscript, ghostview, or any other Postscript viewer or manipulator. The output should look like this:
 
 
  Output of Example 1.3
 

Example 1.4

Use the program igrf to estimate the field on June 1, 1995 in Amsterdam, The Netherlands (52.5 N, 5 E).

Solution

Type the following:

% igrf
1995.5 0 52.5 5 [Input decimal year, altitude (km), lat. (N), long. E)]
 358.0 67.4 48549 [Output D, I, B (nT)]
[type <control-D> to finish]

or use cat as in the first example.
 

Example 1.5

Use the program di_vgp to convert the data in ex1.5 to VGPs.

Solution

Type the following:

% di_vgp < ex1.5

Example 1.6

Use the program vgp_di to convert the data in ex1.6 from VGPs to declination, inclinations. Solution

Type the following:

% cat ex1.3 | vgp_di
335.6 62.9 [Output answer]
[type <control-D> to finish]