Seismic Unix WIKI

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====== First steps with SU ======

===== Data importation =====
[[[[sudoc:su_data_format|SU internal data format]] is closely related to [[https://en.wikipedia.org/wiki/SEG-Y|SEG-Y format]] but is not SEG-Y.

''segyread'' and ''segywrite'' tools must be used to import and export data in and from SU to other processing softwares. 

<WRAP box 800px round center centeralign>
''segyread tape=test.segy verbose=1 | segyclean > test.su''
</WRAP>

Other tools are available to read SEG-2 and some GPR files.

<WRAP download>
You can download a SEGY test file [[https://nextcloud.seismic-unix.org/index.php/s/Bc7RgbwiGdCBZ8A|here]]
</WRAP>

===== Data input and output =====
Most of SU tools use redirection of stdin and stdout [[ wp>https://en.wikipedia.org/wiki/Standard_streams|special unix files]].

SU commands can be run from a console or terminal or embedded in [[ wp>https://en.wikipedia.org/wiki/Shell_script|shell scripts]]. 

For example:
<WRAP box 800px round center centeralign>
''sufilter f=10,20,150,200 amps=0,1,1,0 <data_to_be_filtered.su >bandpass_data.su''
</WRAP>

will apply a band-pass filter to a SU data file and store the result in the file bandpass_data.su ,

<WRAP box 800px round center centeralign>
''sufilter f=10,20,150,200 amps=1,1,0,0 <data_to_be_filtered.su >low_pass_data.su''
</WRAP>

will apply a low pass filter, and

<WRAP box 800px round center centeralign>
''sufilter f=10,20,150,200 amps=0,0,1,1 <data_to_be_filtered.su >high_pass_data.su''
</WRAP>

As other UNIX tools, SU tools can be linked with the pipe mechanism.

For example:

<WRAP box 800px round center centeralign>
''suwind count=10 <other_data.su | sufilter f=10,20,150,200 > new_su_file.su'' 
</WRAP>

''suwind'' reads the file other_data.su, keeps only the first 10 traces and its stdout is linked to the stdin of ''sufilter'' whose stdout is redirected into the file new_su_file.su.The default filter is a trapezoidal bandpass filter.

<WRAP info>
if you are running SU on a multicore/multiprocessor computer with shared memory, the tasks will be distributed by the operating system to different cores/processors.
</WRAP>
===== Structure of a SU command =====

Unlike most of Unix tools SU don't use switches, but parameters with numerical (or text) values

As can be seen in the previous section SU commands are of the form:
  * SU command
  * input and output (unnecessary if one or both are piped)
  * parameters of the form param=value (without spaces around = ), separated by spaces. Some parameters are compulsory, others have default values and are optional.

===== Drawing seismic data =====

Drawing in SU can be done for the screen or to be printed. 
  * Screen drawings are made with [[wp>https://en.wikipedia.org/wiki/X_Window_System|X-window]] tools
  * Printed drawings are made using [[wp>https://en.wikipedia.org/wiki/PostScript|PostScript]] professional DTP page description language.

==== Screen display : ====
=== Variable area bitmap ===

<WRAP box 800px round center centeralign>
 suplane | suxwigb 
</WRAP>

{{:tutorials:suxwigb.png?direct&400 |}}
  
Both SU tools (''suplane'' and ''suxwigb'') are used with their default parameters. ''suplane'' is used to generate some simple seismic traces and ''suxwigb'' is used to display them on screen.\\ By default, ''suxwigb'' represents the seismic signal as the combination of a wiggle trace and variable area.\\ This simple sequence is often used to quickly test test a new SU installation. If you use ''suxwigb'' with too many traces with respect to the picture size and screen resolution (i.e. the number of pixels available to draw a trace), you will get a black box.

=== Variable density ===
<WRAP box 800px round center centeralign>
 suplane | suximage
</WRAP>

{{:tutorials:suximage.png?direct&400 |}}
  
Both SU tools (''suplane'' and ''suximage'') are used with their default parameters. ''suplane'' is used to generate some simple seismic traces and ''suximage'' is used to display them on screen.\\  By default ''suximage'' represents the seismic signal as a column of gray pixels, coding 256 levels of amplitudes. Color mode is available. This drawing mode is suited to represent high number of traces.


==== Printing ====
SU ready-to-print files are coded in the PostScript language. Actually, they are [[wp>https://en.wikipedia.org/wiki/Encapsulated_PostScript|encapsulated]] PostScript files that can be imported in any decent text processing or drawing software. They can also be easily converted to [[wp>https://en.wikipedia.org/wiki/PDF|PDF format]] for better portability.

=== Variable area bitmap ===

<WRAP box 800px round center centeralign>
suplane | supswigb > supswigb.eps
</WRAP>

{{:tutorials:variab_area_bitmap.png?direct&400 |}}
  
Both SU tools (''suplane'' and ''supswigb'') are used with their default parameters. ''suplane'' is used to generate some simple seismic traces and ''supswigb'' is used to generate the encapsulated PostScript picture.\\ By default, ''supswigb'' represents the seismic signal as the combination of a wiggle trace and variable area.\\ The drawing has some differences with ''suxwigb'' drawings, particularly the axes. The drawing itself is a combination of black and white dots and is opaque if you want to superimpose it over an other drawing. 

=== Variable area vector ===

<WRAP box 800px round center centeralign>
suplane | supswigp > supswigp.eps
</WRAP>

{{:tutorials:variab_area_vector.png?direct&400 |}}
  
Both SU tools (''suplane'' and ''supswigp'') are used with their default parameters. ''suplane'' is used to generate some simple seismic traces and ''supswigp'' is used to generate the encapsulated PostScript picture.\\ By default, ''supswigp'' represents the seismic signal as the combination of a wiggle trace and variable area.\\ 
Unlike ''supswigb'' the eps picture is made of lines, so, you get more configuration possibilities. Between the lines, the picture is empty and partly transparent. Using this mode to represent a high number of traces can lead to a very big file.

=== Variable density ===

<WRAP box 800px round center centeralign>
suplane | supsimage > supsimage.eps
</WRAP>

{{:tutorials:variab_dens.png?direct&400 |}}
  
Both SU tools (''suplane'' and ''supsimage'') are used with their default parameters. ''suplane'' is used to generate some simple seismic traces and ''supsimage'' is used to display them on screen.\\ By default, ''supsimage'' represents the seismic signal as gray levels.\\ Color mode is available.



===== Getting some help =====
If you don't know the name of the SU command you need, you can try ''sufind migration'', for example, to get the list of SU modules related to migration.

SU modules displays their so-called selfdoc when you type a SU command without any parameter.
You can get a few more informations about a tool, using ''sudoc suplane'', for example.


<WRAP info>
You can also subscribe to the [[ https://mailman.seismic-unix.org/listinfo/seisunix | SU mailing list ]] to get in touch with other SU users around the world.
</WRAP>

 --- //[[dominique.rousset@univ-pau.fr|Dominique ROUSSET]] 2019/07/23 11:50//
{{gravatar>dominique?l}}