Applied Geophysics
Gravity Modeling Assignment

There is a program available for interactive gravity modeling called Xgrav. A manual for this program can be found at:

In order to get some practice with seeing how different bodies can produce different anomalies, try running the program Xgrav on an example problem. Here are the steps you should take:

1. Login to a SUN workstation, pferably one running SOLARIS (like gretchen in the computer room, and probably most in the SUN labs on campus). Login as "Geophys". I'll give you a password in class.

2. There is a file called Homework.anomaly in the home directory. This contains a trial data set that you can try to model.

3. Start Xgrav and read in the Homework.anomaly file as a data file.

4. Select the "Enter Body" option to get started with a model.

5. Change the shape and contrast of the body to see if you can explain the data.

6. When you're finished, save your work to files that will be easy for you to identify (use your name or initials as part of the filename, for example).

7. When you have a model you like, e-mail it to me.

Notes on using Xgrav from other (non-gretchen) workstations:

If you want to run Xgrav from another workstation other than gretchen, do so by logging into gretchen from that workstation and running it remotely. Here are the steps:

1. On the workstation you are using, type

   xhost +
   

   This will allow you other workstations to draw on the screen.

2. Remotely login to gretchen like this:

   rlogin gretchen.geo.rpi.edu -l [username]
   

   where [username] is your Geology login name or Geophys.

3. Gretchen needs to know where to send pictures, so set the DISPLAY to the screen you are using. For example, if you are logged into hanya.geo.rpi.edu and you are remotely logged into gretchen, type

   setenv DISPLAY hanya.geo.rpi.edu:0
   

   in the window where you have logged into gretchen.

4. If you logged in under another username other than Geophys, you may have to set up two more environment variables to get this to work. The first tells Xgrav where certain graphics libraries are, and is:

   setenv LD_LIBRARY_PATH /usr/openwin/lib
   

   The other command is to add the path /users/generic/sun4 to your search path. Either edit your .cshrc file to include this and then do a "source .cshrc" or just refer to Xgrav by its total path name as

   /users/generic/sun4/Xgrav