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

Chapter 2: RUDIMENTS OF ROCK MAGNETISM

Example 2.1

Plot the thermomagnetic data in file ex2.1 using plotxy. Then convert to absolute temperature and find the inverse. Plot these data using plotxy.

Solution:

Type the boldfaced commands (the computer responses are in normal typeface):

% plotxy
Enter commands for graph 1
file ex2.1
read
xlabel Temperature
ylabel M
plot 1 1
 

-------------------
PostScript file written to: mypost
========== --------------
Enter commands for graph 2
stop

These commands cause plotxy to generate the postscript file mypost.
 

Example 2.2

Plot the thermomagnetic data in file ex2.1 using plotxy. Then convert to absolute temperature and find the inverse. Plot these data using plotxy.

Solution:

Type the boldfaced commands (the computer responses are in normal typeface):

Type:

% nawk '{print 1/($1+273),$2}' ex2.1 > ex2.1a

The Unix utility nawk is similar to awk and performs a number of spread-sheet like operations on data files.

To plot the inverted temperatures, type:

% plotxy
Enter commands for graph 1
file ex2.1a
read
xlabel Inverse Temperature
ylabel M
plot 1 1
-------------------
PostScript file written to: mypost
========== --------------
Enter commands for graph 2
stop

This generates the postcript file mypost.
 

Example 2.2

Use the program curie to calculate the Curie temperature of the data contained in file ex2.1. First scan through a range of smoothing intervals from 1 to 100, and then choose the optimal smoothing interval (the smallest interval necessary to isolate the correct peak in the second derivative). Finally, repeat this, but truncate the data set to between 400 to 600.

Solution:

First type:

% curie -s 1 100 1 < ex2.1

which produces a list of Curie temperatures for smoothing intervals from 1 to 100C at 1C invervals:

Tc = 203
.
.
.

Now type:

% curie -lsp 20 1 100 1 < ex2.1 | plotxy

This causes plotxy to produce a postscript file mypost shown:

It may be that there are several Curie temperatures in a particular data set and that you wish to focus in on one of them. The curie program allows truncation of the data set to a given interval by specifying Tmin and Tmax with the -t option.

To complete the excercise, type the following:

% curie -lspt 20 1 100 1 400 600 < ex2.1 | plotxy View the  mypost file:
 
 

Example 2.3

Use the program hystcrunch to calculate the hysteresis parameters, M_r, M_s, H_c, H_cr' and H_cr'' from the data in file ex2.3. These data are in the raw format that is the output from the available Micromag 2900 alternating gradient magnetometer. NB: retaining only the first 30 Fourier harmonics results in a smoother Delta M/dH curve.

Solution Type the following: % hystcrunch -mt 30 < ex2.3 | plotxy

This causes plotxy to produce a postcript file mypost: