Geophysical Exploration of Crustal Structure

Exercise (Preparation)

Preparation > Exercise 1

Basic understanding of the Unix operation system is a prerequisite for this exercice. Self-learning is necessary if you do not get accustomed to it. Please consult the instructor.

In this exercise, you will learn seismic data processing using Seismic Un*x (hereafter SU).

Reference sites:

Preparation

Use SU via network

The following explanation premises that you are going to login daikoku.seis.nagoya-u.ac.jp via "ssh" and use "X" window system.

To execute the exercise, the following network environments are recommended.

Macintosh PC (MacOS is a Unix)
- You can use PCs (Macs) in the computer room (E405). This is the easiest.
Windows PC that runs X terminal emulator, For example,
- Astec-X (Lintk to English site became unavailable.)
- Cygwin/X
- Terminal software
  - PuTTY
  - Tera Term
  and X server, for example,
  - VcXsrv
  (My recommendation to you is to use PuTTY + VcXsrv for this exercise, if you do not have favorites.)
  Settings (to connect "daikoku" using PuTTY + VcXsrv)

WS or PC running Linux + X (including a virtual machine on Windows by VMware, VirtualBox, and WSL) and network connection to daikoku.seis.nagoya-u.ac.jp by yourself.

If you do not have an account on 'daikoku', please ask the instructor.

Installing SU in your computer

You can skip here if not interested. Go to the next section.

You can install SU in your Unix environment, including PC Unix such as cygwin, any virtual machine such as VMware and VirtualBox, and WSL available only after Windows 10, if you find it useful. Install is fairly easy. Please consult the instructor if interested.

Connection and login

Using a Mac in the computer room (E405), open a UNIX terminal by clicking icons of 'X11' or 'Terminal'.
For other environments, open an X-Terminal.
Login 'daikoku' via ssh,
```
$ ssh -X username@daikoku.seis.nagoya-u.ac.jp
$ ssh -X username@daikoku
 
```
Here "username" is your username.
Using putty+Vcsrv from Windows PC, connect to "daikoku" using putty.

Setting Environments

Set the following environment variables before using SU.

If you use "bash" (this is the default of most Linux distribution)
```
 from here
 ---------
 export CWPROOT=/usr/local/cwp
 export PATH=$CWPROOT/bin:$PATH
 ---------
 till here
 
```
Append the above description to "~/.bashrc" using an editor (vi, Emacs, etc.)
```
 $ vi ~/.bashrc
 $ emacs ~/.bashrc &
 
```
Or, add the above settings using below.
```
 $ mv ~/.bashrc .bashrc.bak
 $ cat .bashrc.bak /export/watanabe/exercise/dot.bashrc.add > ~/.bashrc
 
```
Make sure that the setting was made.
```
 $ cat ~/.bashrc
 
```
Reflect the new settings.
```
 $ source ~/.bashrc
 
```
Then, make sure that the environment variables "CWPROOT" and "PATH" are properly set.
```
 $ printenv
 
```
If you use "csh" or "tcsh"
```
 from here
 ---------
 setenv CWPROOT /usr/local/cwp
 setenv PATH $CWPROOT/bin:$PATH
 ---------
 till here
 
```
Append the above description to "~/.cshrc" and execute "source ~/.cshrc".
Make sure that the setting was renewed.
```
 $ cat ~/.cshrc
  
```
Reflect the new settings.
```
 $ source ~/.cshrc
  
```
Then, make sure that the environment variables "CWPROOT" and "PATH" are properly set.
```
 $ setenv
 
```

These environment variables will be automatically set after you open new shells or from your next login. However, sometimes your setting will not work due to your way of access to the server. If you fail to execute SU commands (An error message, "command not found" appears), be sure to check these environment variables are properly set and if not, execute the "source" command manually.

Data

The data you are going to use in this exercise are located in the following directory on 'daikoku';

   daikoku.seis.nagoya-u.ac.jp:/export/watanabe/exercise

Copy the data and the scripts in the directory to your working directory.

$ mkdir exercise         (or any directory you like for this exercise)
$ cd excercise           (move into the directory)
$ cp /export/watanabe/exercise/demo*.su .       (copy the demo files)
$ cp /export/watanabe/exercise/*.sh .           (copy scripts)
$ cp /export/watanabe/exercise/*.par .          (copy parameter file for a script)
$ ln -s /export/watanabe/exercise/Nshots.su Nshots.su        (create a link to datafile) 
$ ln -s /export/watanabe/exercise/Nstack.su Nstack.su        (create a link to datafile)

'*' represents any character, therefore, multiple files are copied.

``Nshots.su'' is an original data record (shot records) to be processed in this exercise.
``Nstack.su'' is a processed record.

For these field datasets, create a symbolic link (like a short-cut used in the Windows system) to each data file, not copying them to your working directory, because the file size of the dataset is large.

If you are not using "daikoku", please ask the instructor.

Basic usage

SU program, like other Unix commands, "reads data from Standard-input, processes them and writes the result to Standard-output".

"<" input from file
">" output to file
" | " pipe

Basic syntax are like,

$ su-command opt1=value1 opt2=value2 .... (options) < input-data > output-data
$ su-command opt1=value1 opt2=value2 .... (options) < input-data | next-process ... > output-data
$ previous-process | su-command opt1=value1 opt2=value2 .... (options) | next-process ...

(Tip) The usage of a command is displayed when you type the command without any option. You can learn how to use the command.

Execute the following commands and be sure to check that you can see a brief help on these commands.

$ suplane
$ suxwigb
$ xwigb
$ suximage
$ ximage

Execute the following commands and be sure to check that you can see some plots come up properly.

$ suplane | suxwigb &
$ suplane | suximage &

If you encounter errors, go back to "Setting" and do again.

'suplane' generates a simple wave record.
'suxwigb' displays waveform data.
'suximage' displays image (B/W or color).

Try the followings.

Zoom using click and drag of the left mouse button. The left click displays the original.
Change color palette by pressing 'h', 'H', 'r', 'R' keys in case of image plot.
Obtain the pointer location by clicking the middle mouse button. The coordinate will be displayed on the top-left.
Destroy the window by pressing 'q'.

Now you are ready to do your exercise.

If you fail to complete the above procedure, this means that you can not proceed any further. Consult the instructor or your friends and ask for help.

Homework

Execute the following command and display the result. Then change the aspect ratio, display area (zoom), and color scale so that you will see the structure well.

$ suximage < Nstack.su perc=?? &

Namely, figures that resemble the following figure are insufficient.

'perc=' is a percentile value for display clip. Try different numbers from 95 to 100 to 'perc=??' then see how the value affects the display.
Try to change the size and the aspect ratio of the image, zooming, and color palette.