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Last update:
16 May 2014

USING SeismicUnix


1.  Conversion of SEG-B, SEG-C to Seismic Unix format


2.  SEG-Y data format and how it differs from the Seismic Unix format


In order to process data with Seismic Unix you need to be familiar with the layout of SEG-Y files and how it differs from the Seismic Unix (SU) data format. First, get the SEG-Y standard from The Society of Exploration Geophysicists (SEG):

The SEG-Y format specification from SEG:

  • First version 1975
  • Rev. 1 2002
    A new feature in this revision is the possibility to store data in IEEE 754 format (see page 6).

This is how a SEG-Y file looks like:

SEG-Y structure
SEG-Y format structure.

The SU data format consists of the trace data blocks ONLY. The reel identification header can later be inserted when data is exported in the SEG-Y format.

SU files stores floating point values in "the native binary format of the machine you are running the programs on" - quote from section 3.1.1 (p.21) of the SeismicUnix manual.

It's difficult to spot a mix-up of IBM floating point format (as used in SEG-Y files) and IEEE 754 floating point format (the floating point format used by e.g. PCs). Here's some background information.

3.  SEG-Y Reel Identification Header


See this document (local copy).

3.1  The 3200 byte SEG-Y EBCDIC Reel Header


12345678901234567890123456789012345678901234567890123456789012345678901234567890
C 1 CLIENT                        COMPANY                       CREW NO         
C 2 LINE            AREA                        MAP IS                          
C 3 REEL NO           DAY-START OF REEL     YEAR      OBSERVER                  
C 4 INSTRUMENT: MFG            MODEL            SERIAL NO                       
C 5 DATA TRACES/RECORD        AUXILIARY TRACES/RECORD         CDP FOLD          
C 6 SAMPLE INTERVAL         SAMPLES/TRACE       BITS/IN      BYTES/SAMPLE       
C 7 RECORDING FORMAT        FORMAT THIS REEL        MEASUREMENT SYSTEM          
C 8 SAMPLE CODE: FLOATING PT     FIXED PT     FIXED PT-GAIN     CORRELATED      
C 9 GAIN  TYPE: FIXED     BINARY     FLOATING POINT     OTHER                   
C10 FILTERS: ALIAS     HZ  NOTCH     HZ  BAND     -     HZ  SLOPE    -    DB/OCT
C11 SOURCE: TYPE            NUMBER/POINT        POINT INTERVAL                  
C12     PATTERN:                           LENGTH        WIDTH                  
C13 SWEEP: START     HZ  END     HZ  LENGTH      MS  CHANNEL NO     TYPE        
C14 TAPER: START LENGTH       MS  END LENGTH       MS  TYPE                     
C15 SPREAD: OFFSET        MAX DISTANCE        GROUP INTERVAL                    
C16 GEOPHONES: PER GROUP     SPACING     FREQUENCY     MFG          MODEL       
C17     PATTERN:                           LENGTH        WIDTH                  
C18 TRACES SORTED BY: RECORD     CDP     OTHER                                  
C19 AMPLITUDE RECOVERY: NONE      SPHERICAL DIV       AGC    OTHER              
C20 MAP PROJECTION                      ZONE ID       COORDINATE UNITS          
C21 PROCESSING:                                                                 
C22 PROCESSING:                                                                 
C23                                                                             
C24                                                                             
C25                                                                             
C26                                                                             
C27                                                                             
C28                                                                             
C29                                                                             
C30                                                                             
C31                                                                             
C32                                                                             
C33                                                                             
C34                                                                             
C35                                                                             
C36                                                                             
C37                                                                             
C38                                                                             
C39                                                                             
C40 END EBCDIC  

3.2  The 400 byte SEG-Y Binary Reel Header


--------------------------------------------------------------------------------
Bytes         Description                                                       
--------------------------------------------------------------------------------
001 - 004     Job identification number.                                        
005 - 008  *  Line number.                                                      
009 - 012  *  Reel number.                                                      
013 - 014  *  Number of data traces per record.                                 
015 - 016  *  Number of auxiliary traces per record.                            
017 - 018  *  Sample interval of this reel's data in microseconds               
019 - 020     Sample interval of original field recording in microseconds.      
021 - 022  *  Number of samples per trace for this reel's data.                 
023 - 024     Number of samples per trace in original field recording.          
025 - 026  *  Data sample format code:                                          
                  1 = 32-bit IBM floating point                                 
                  2 = 32-bit fixed-point (integer)                              
                  3 = 16-bit fixed-point (integer)                              
                  4 = 32-bit fixed-point with gain code (integer)               
           $      5 = 32-bit IEEE floating point                                
           $      6,7 = Not currently used                                      
           $      8 = 8-bit, two's complement integer)                          
027 - 028  *  CDP fold (expected number of data traces per ensemble).           
029 - 030     Trace sorting code:                                               
                  1 = as recorded                                               
                  2 = CDP ensemble                                              
                  3 = single fold continuous profile                            
                  4 = horizontally stacked                                      
031 - 032     Vertical sum code (1 = no sum, 2 = two sum, ...)                  
033 - 034     Sweep frequency at start in Hertz.                                
035 - 036     Sweep frequency at end in Hertz.                                  
037 - 038     Sweep length in milliseconds.                                     
039 - 040     Sweep type code:                                                  
                  1 = linear                                                    
                  2 = parabolic                                                 
                  3 = exponential                                               
                  4 = other                                                     
041 - 042     Trace number of sweep channel.                                    
043 - 044     Sweep trace taper length at start in milliseconds.                
045 - 046     Sweep trace taper length at end in milliseconds.                  
047 - 048     Taper type code:                                                  
                  1 = linear                                                    
                  2 = cosine squared                                            
                  3 = other                                                     
049 - 050     Correlated data traces (1 = no, 2 = yes).                         
051 - 052     Binary gain recovered (1 = yes, 2 = no).                          
053 - 054     Amplitude recovery method code:                                   
                  1 = one                                                       
                  2 = spherical divergence                                      
                  3 = AGC                                                       
                  4 = other                                                     
055 - 056  *  Measurement system (1 = meters, 2 = feet).                        
057 - 058     Impulse signal polarity (increase in pressure or upward           
              geophone case movement gives 1=negative or 2=positive number).    
059 - 060     Vibratory polarity code (seismic lags pilot signal by):           
                  1 = 337.5 to 22.5 degrees                                     
                  2 = 22.5 to 67.5 degrees                                      
                  3 = 67.5 to 112.5 degrees                                     
                  4 = 112.5 to 157.5 degrees                                    
                  5 = 157.5 to 202.5 degrees                                    
                  6 = 202.5 to 247.5 degrees                                    
                  7 = 247.5 to 292.5 degrees                                    
                  8 = 292.5 to 337.5 degrees                                    
061 - 400     Unassigned (for optional information)s                            

* strongly recommended
$ Defined in rev 1 of the SEGY standard

4.  SEG-Y Trace Identification Header


The 240-byte binary trace header consists of 2-byte and 4-byte integers:

--------------------------------------------------------------------------------------------------------
Byte #    2/4-byte   SU Keyword    Description                                                          
--------------------------------------------------------------------------------------------------------
001 - 004    4     *  tracl        Trace sequence number within line.                                   
005 - 008    4        tracr        Trace sequence number within reel.                                   
009 - 012    4     *  fldr         Original field record number.                                        
013 - 016    4     *  tracf        Trace sequence number within original field record.                  
017 - 020    4        ep           Energy source point number.                                          
021 - 024    4        cdp          CDP ensemble number.                                                 
025 - 028    4        cdpt         Trace sequence number within CDP ensemble.                           
029 - 030    2     *  trid         Trace identification code:                                           
                                       1 = seismic data                                                 
                                       2 = dead                                                         
                                       3 = dummy                                                        
                                       4 = time break                                                   
                                       5 = uphole                                                       
                                       6 = sweep                                                        
                                       7 = timing                                                       
                                       8 = water break                                                  
                                       9+ = optional use                                                
                                       SU specific id codes, look here                                  
031 - 032    2       nvs           Number of vertically summed traces yielding this trace.              
033 - 034    2       nhs           Number of horizontally stacked traced yielding this trace.           
035 - 036    2       duse          Data use (1 = production, 2 = test).                                 
037 - 040    4       offset        Distance from source point to receiver group.                        
041 - 044    4       gelev         Receiver group elevation.                                            
045 - 048    4       selev         Surface elevation at source.                                         
049 - 052    4       sdepth        Source depth below surface.                                          
053 - 056    4       gdel          Datum elevation at receiver group.                                   
057 - 060    4       sdel          Datum elevation at source.                                           
061 - 064    4       swdep         Water depth at source.                                               
065 - 068    4       gwdep         Water depth at receiver group.                                       
069 - 070    2       scalel        Scalar for elevations and depths (+ = multiplier, - = divisor).      
071 - 072    2       scalco        Scalar for coordinates (+ = multiplier, - = divisor).                
073 - 076    4       sx            X source coordinate.                                                 
077 - 080    4       sy            Y source coordinate.                                                 
081 - 084    4       gx            X receiver group coordinate.                                         
085 - 088    4       gy            Y receiver group coordinate.                                         
089 - 090    2       counit        Coordinate units (1 = length in meters or feet, 2 = arc seconds).    
091 - 092    2       wevel         Weathering velocity.                                                 
093 - 094    2       swevel        Subweathering velocity.                                              
095 - 096    2       sut           Uphole time at source.                                               
097 - 098    2       gut           Uphole time at receiver group.                                       
099 - 100    2       sstat         Source static correction.                                            
101 - 102    2       gstat         Receiver group static correction.                                    
103 - 104    2       tstat         Total static applied.                                                
105 - 106    2       laga          Lag time between end of header and time break in milliseconds.       
107 - 108    2       lagb          Lag time between time break and shot in milliseconds.                
109 - 110    2       delrt         Lag time beteen shot and recording start in milliseconds.            
111 - 112    2       muts          Start of mute time.                                                  
113 - 114    2       mute          End of mute time.                                                    
115 - 116    2    *  ns            Number of samples in this trace.                                     
117 - 118    2    *  dt            Sample interval of this trace in microseconds.                       
119 - 120    2       gain          Field instrument gain type code:                                     
                                       1 = fixed                                                        
                                       2 = binary                                                       
                                       3 = floating point                                               
                                       4+ = optional use                                                
121 - 122    2       igc           Instrument gain constant.                                            
123 - 124    2       igi           Intrument early gain in decibels.                                    
125 - 126    2       corr          Correlated (1 = no, 2 = yes).                                        
127 - 128    2       sfs           Sweep frequency at start.                                            
129 - 130    2       sfe           Sweep fequency at end.                                               
131 - 132    2       slen          Sweep length in milliseconds.                                        
133 - 134    2       styp          Sweep type code:                                                     
                                       1 = linear                                                       
                                       2 = parabolic                                                    
                                       3 = exponential                                                  
                                       4 = other                                                        
135 - 136    2       stas          Sweep taper trace length at start in milliseconds.                   
137 - 138    2       stae          Sweep taper trace length at end in milliseconds.                     
139 - 140    2       tatyp         Taper type code:                                                     
                                       1 = linear                                                       
                                       2 = cosine squared                                               
                                       3 = other                                                        
141 - 142    2       afilf         Alias filter frequency.                                              
143 - 144    2       afils         Alias filter slope.                                                  
145 - 146    2       nofilf        Notch filter frequency.                                              
147 - 148    2       nofils        Notch filter slope.                                                  
149 - 150    2       lcf           Low cut frequency.                                                   
151 - 152    2       hcf           High cut frequency.                                                  
153 - 154    2       lcs           Low cut slope.                                                       
155 - 156    2       hcs           High cut slope.                                                      
157 - 158    2       year          Year data recorded.                                                  
159 - 160    2       day           Day of year.                                                         
161 - 162    2       hour          Hour of day (24-hour clock).                                         
163 - 164    2       minute        Minute of hour.                                                      
165 - 166    2       sec           Second of minute.                                                    
167 - 168    2       timbas        Time basis (1 = local, 2 = GMT, 3 = other).                          
169 - 170    2       trwf          Trace weighting factor for fixed-point format data.                  
171 - 172    2       grnors        Geophone group number of roll switch position one.                   
173 - 174    2       grnofr        Geophone group number of first trace of original field record.       
175 - 176    2       grnlof        Geophone group number of last trace of original field record.        
177 - 178    2       gaps          Gap size (total number of groups dropped).                           
179 - 180    2       otrav         Overtravel associated with taper (1 = down/behind, 2 = up/ahead).    
181 - 240                          Unassigned (for optional information).
 * strongly recommended

For SU assignments of positions 181 - 240, look here.

5.  Relationship between fldr, ep, tracl, tracr, tracf


Let's reiterate:

  • fldr = Original field record number
  • ep = Energy source point number
  • tracl = Trace sequence number within LINE
  • tracr = Trace sequence number within REEL (or file)
  • tracf = Trace sequence number within original field record

Assumptions:

  • Each recording consists of three traces
  • fldr matches ep (don't need to), and starting at 1
  • tracl matches tracr (it won't if data from one line is recorded on several files)

6.  Seismic Unix (SU) links


7.  SU Quick Install, version 40


Assuming CWPHOME=/usr/local/SU and that you're on a Linux Intel box (we're using Fedora 7).

1. In /etc/profile (or profile.local):
      CWPROOT="/usr/local/SU"
      PATH="$PATH:/usr/local/SU/bin"
      export PATH CWPROOT
   Log out, then in again.

2. Do NOT install as root.
   Get ftp://ftp.cwp.mines.edu/pub/cwpcodes/cwp_su_all_40.tgz
   Save in /usr/local/SU
   First make this directory (as root), then change ownership:
       mkdir /usr/local/SU
       chown xxx /usr/local/SU
   (assuming you are user xxx)
   Uncompress:
       cd /usr/local/SU/
       tar -xzvf cwp*

3. First install these packages on your linux box : compat-gcc-34 (else suxgraph will not work properly), all lesstif packages. 

4. Rename /usr/local/SU/Makefile.config:
        mv Makefile.config Makefile.config.original
   Download this Makefile.config file and put it in /usr/local/SU/src.
   Note: From release 39 (this configuration will provide support for large files > 2GB.) 

5. You're not root, are you? If not:
      cd /usr/local/SU/src
      make install
      make xtinstall
   If you want to compile additional code, check README_TO_INSTALL

6. Test the installation:
      suplane | suxgraph &			
      suplane | suximage &
   Use <CTRL>+h to change colour palette, to get this (click to enlarge):
Click to enlarge.

7.1  segdread: Important note on gcc version 3.2.2 (RedHat 9.0), gcc version 3.3.4 (SUSE 9.2)


There are problems with gcc version 3.2.2 (RedHat 9.0), and version 3.3.4 (SUSE 9.2) - the segdread will be broken. To recompile segdread first get the compat-gcc RPM's (or you can download a binary segdread compiled on FC1 Linux with compat-gcc from here; place it in the $CWPROOT/bin directory, overwriting the old version):

   compat-gcc-7.3-2.96.118.i386.rpm
   compat-gcc-c++-7.3-2.96.118.i386.rpm
   compat-libstdc++-7.3-2.96.118.i386.rpm
   compat-gcc-g77-7.3-2.96.118.i386.rpm

Then

   rpm -Uvh compat*

You must first remove or rename the original version of $CWPROOT/bin/segdread before proceeding, Then edit Makefile.config by setting

   CC = gcc296

Recompile segdread by

   make sfremake

You can also compile SU from scratch with gcc version 2.9.6.

Department of Earth Science
University of Bergen
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