GEPH316 Field Data: CWP/SU Package

GEPH316 Seismic Data Processing

Field Data Workshop 2000/B>

3 CWP/SU Package


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CWP/SU Seismic Unix philosophy

The CWP/SU package is a seismic data processing package, designed for research work. It originated at the Center for Wave Phenomena CWP at Colorado School of Mines, Colorado, USA.
The package has been called Seismic Unix SU to emphasise the structure and philosophy of the software, which is very similar to that of the Unix open operating system.
- It works on a standard file format, the SEG-Y standard produced by the Society for Exploration Geophysicists.
- It consists of numerous small, simple, single-purpose individual tools, rather than one immense, unwieldy program that is difficult to learn. You only need to learn about those tools you need.
- The power of the package arises from being able to pipe the information output by one command into the input of the next command, just as in Unix filters.
- The toolset is easily extensible, either by programming new commands or by calling the existing commands from simple macros.
- Most operating values are specified by means of parameter words.
- There is extensive on-line help direct from Colorado and most commands are self-documenting.
- SU is in the public domain and is available for downloading from CWP.
SU makes extensive use of X windows facilities for terminal graphics display and Postscript facilities for printing.
SU can be run on most Unix systems, with suitable configuration.

Piping files through SU commands

Unix uses the concept of pipes and filters to explain the flow of data from one command to the next.
The input pipe is denoted by the left arrowhead < and is used to pipe information from a disk file into a command as:
```
sucommand <inputfile
```
If no input pipe is supplied, input will be expected from the keyboard and the command will hang until input is given. Keyboard input can be terminated using Ctrl+D or Ctrl+C.
The output pipe is denoted by the right arrowhead > and is used to pipe information from a command into a disk file as:
```
sucommand >outputfile
```
If no output pipe is supplied, output will be directed to the screen and lots of unpleasant information may be printed. Output can be terminated using Ctrl+C. In desparation, try Ctrl+Z or Ctrl+X !
The input and output pipes may used together in a command as:
```
sucommand <inputfile >outputfile
```
The append pipe is denoted by two right arrowheads >> and is used to pipe information onto the end of an existing disk file using a command as:
```
sucommand >>oldoutputfile
```
The input and output pipes require physical disk files, which take up space and may need clearing up at the end of the operation. It is possible to avoid creating unnecessary physical files by piping the output from one command directly into the input of the next command using the general pipe vertical line symbol | as:
```
sucommand1 <inputfile | sucommand2 >outputfile
```
Some commands do not produce a physical file. For example, the suwigb plotting command takes in a file, but displays the output in an X windows plot. Therefore it is often used as a sink for the end of a command chain as:
```
sucommand1 <inputfile | sucommand2 | suxwigb
```
Most commands require a variety of parameters. Usually the parameters take the form of a keyword, an equals sign and the value, for example
```
sucommand1 <inputfile param1=5 param2='text info'
```
Do not leave spaces on either side of the equals sign or the parameter may not have the effect intended.

SU on-line help

Seismic Unix provides a variety of on-line help facilities.
Most of the SU commands are self-documenting. Just by typing the command name alone, the command gives a simple explanation of what it is for, the parameters it needs and how to use it. Try:
```
suxwigb
```
There is an extensive on-line help tutorial information direct from the Internet Web site in Colorado. One example of their help pages is stored locally.
Locally, the following SU information is available rapidly.
- suhelp lists the names of the programs in the distributed version of the package.
- suname is a program that lists the names and a one-line description of all the programs and libraries.
- sudoc is a utility that lists the self-documentation of all programs in the package. Try:
```
sudoc suxwigb
```
- sufind is a program that searches the self-documentations for a given string. If you cannot remember the name of a command, or if you do not know whether a particular type of command exists, you can used the sufind command to search for information. Try both of these now:
```
sufind
sufind filter
```

SU programs that manipulate the trace headers in the seismic data use specific names called "keywords" to identify the header fields. The sukeyword program enables the user to list the definition file for the keywords. For example,

% sukeyword fldr
...skipping
        int tracr;     /* trace sequence number within reel */
        int fldr;      /* field record number */
        int tracf;     /* trace number within field record */
        int ep;        /* energy source point number */
        int cdp;       /* CDP ensemble number */
...

Beware that the physical units applied to the header words can vary. For example, the sampling interval header word dt is stored in the seismic data in the form of microseconds e.g. dt=250, but some commands require it as a parameter in the form of seconds e.g. dt=0.00025.


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