Go to the list of seismic processes.      Go to SIOSEIS introduction.
    This is the story of how I processed some "single channel"
data from the Ewing.  The data were converted into SEG-Y before
being given to me.
ls -l ew*
-rwxr-xr-x    1 henkart  21       612263952 Nov 14 13:42 ew9513_line7.segy


    The data contain 4 channels, where the close group has a length of
12.5m and is 150m from the fantail.  The next group is a 25m group and
then there are two 50m groups.

lsd ew9513_line7.segy 1 12
      SHOT   TR       RP    TR ID  RANGE DELAY NSAMPS    SI   YR DAY HR MIN SEC
     81884     1       0     0  1      0     0   6144  2000   96  13 13  50   5
     81884     2       0     0  1      0     0   6144  2000   96  13 13  50   5
     81884     3       0     0  1      0     0   6144  2000   96  13 13  50   5
     81884     4       0     0  1      0     0   6144  2000   96  13 13  50   5
     81884     5       0     0  1      0     0   6144  2000   96  13 13  50   5
     81884     6       0     0  1      0     0   6144  2000   96  13 13  50   5
     81884     7       0     0  1      0     0   6144  2000   96  13 13  50   5
     81884     8       0     0  1      0     0   6144  2000   96  13 13  50   5
     81885     1       0     0  1      0     0   6144  2000   96  13 13  50  20
     81885     2       0     0  1      0     0   6144  2000   96  13 13  50  20
     81885     3       0     0  1      0     0   6144  2000   96  13 13  50  20
     81885     4       0     0  1      0     0   6144  2000   96  13 13  50  20


    The first thing I did was to get just look a small 50 shots of each
channel.
  • script #1 - Plot 50 shots of each trace      trace 1s plot      trace 2s plot      trace 3s plot      trace 4s plot
    
    Notice that trace 3 and trace 4 are significantly better than
    trace 1 or trace 2.  I worked with trace 4 only to determine some
    other processing parameters.
    
    Waterguns have higher frequency content than airguns and a typical
    filter bandpass is 30x130.  Typically, the watergun precurser is
    around 35Hz.
    
  • script #2 - Filter and AGC      trace 4s plot
    
    Sometimes AGC make the data look noisy, so I tried GAINS instead.
    
  • script #2a - Filter and GAINS
    
    That was a bad choice of GAINS parameter ALPHA, so try alpha .5
    
  • script #2b - Filter and GAINS      gains alpha .5
    
    Change the plot scale so the plot isn't as "scrunched".
    
  • script #2c - change vscale      plot vscale 5
    
    Now, let's look at 400 shots rather than 50
    
  • script #3 - read 400 shots      plot of 400 shots
    
    Stack (addition) of any type of signals reduces the random noise by
    the square root of the number of signals summed.  E.G. Adding two
    traces together will reduce the random noise by SQRT(2).  
    Trace 3 and trace 4 are quite good and are similar streamer sections,
    so just use those two traces in the stack.  
    
    Trace 3 and 4 are 50 meters apart and the pop interval is 79m, so
    simply sum the adjacent traces rather than sorting (gathering) into
    CDPs or RPs.
    Process STACK sums traces until an "end of gather" flag is detected.
    Process DISKIN parameter NTRGAT sets the "end of gather" flag after
    NTRGAT traces are read.
    
  • script #4 - stack traces 3 and 4      plot of 400 stacked shots

    Go to the list of seismic processes.      Go to SIOSEIS introduction.