PROCESS MIX
                                ------- ---

Parameters, alphabetically:
dip      fno      hdr      ihdr     lhdr     lno 
maxlen   type     weight


Document Date: June, 2000

Process MIX performs a running, weighted, dip mix.  Mix is defined to be
the sum or addition of adjacent traces (in a numerical sense).   There
are three types of mix: 

1)   A running roll-along mix - The mix crosses record boundaries.  If
     the data are shots, the last trace of a shot is mixed with the
     first trace of the next shot.  e.g. A three trace equally weighted
     zero dip unweighted running mix will output the following traces:
     trace 1 = input traces 1
     trace 2 = input traces 1+2
     trace 3 = input traces 1+2+3
     trace 4 = input traces 2+3+4
     trace 5 = input traces 3+4+5
     etc.

2)   A running record mix - The mix stops at the end of each shot and
     starts over on the next shot.  A three trace equally weighted zero
     dip running record mix of 24 trace shots will output the following:
     trace 1 = input traces 1
     trace 2 = input traces 1+2
     trace 3 = input traces 1+2+3
     trace 4 = input traces 2+3+4
          .     .
          .     .
     trace 24 = input traces 22+23+24

3)   A record mix - This mix starts over after every mix set and does
     not output the tapered traces.  e.g. A three trace record mix of
     24 trace shots will output the following:
     trace 1 = input traces 1+2+3
     trace 2 = input traces 4+5+6
     trace 3 = input traces 7+8+9
          .        .
          .        .
     trace 8 = input traces 22+23+24


A weighted or tapered mix allows each trace to be independently scaled
prior to the mix.  Referring to example 1 above, a 1 2 1 weighted mix
will have output trace 3 containing (trace1)*1+(trace2)*2+(trace3)*1,
output trace 4 = (trace2)*1.+(Trace3)*2.+(Trace4)*1.

A dip mix is a mix with each trace shifted in time prior to the mix.
The time shift is relative to the first trace within the mix so that the
first input trace is not shifted, the second is shifted by dip seconds,
the third by dip*2 seconds.

Each parameter list must be terminated with the word END.  The entire
set of mix parameters must be terminated by the word END.

HEADER MIX
------ ---
A simple ship heave removal scheme required the averaging of the automatic
water bottom picks which were placed in the SEG-Y trace header by process
WBT.  Averaging is a mix, so trace header mixing may be done in process
MIX by using parameters HDR or LDR or IHDR.  When using these parameters
the normal trace mix is turned off by setting parameter TYPE to 4.  The
user may override TYPE 4 by specifying it to 1-3.  Up to 100 weights may
be given when doing TYPE 4 (header) mix.

THE PARAMETER DICTIONARY
--- --------- ----------

WEIGHT - A list of weights to use in the mix.  The total number of
         weights given indicates the number of traces in the mix;
         e.g. a 3 trace equally weighted mix will be done by giving
         weight 1 1 1.  At least 2 weights must be given and no more
         than 10 trace weights or 100 header weights may be given.
         Required.

TYPE   - The type of mix to be performed.
       = 1, Running mix.
       = 2, Running record mix.
       = 3, Record mix.
       = 4, Header mix without a data trace mix.
         Preset = 1     e.g. type 3

DIP    - The amount of shift, in seconds, to apply to successive input
         traces within each mixed trace.
         Preset=0.

MAXLEN - The maximum length, in seconds, of the largest input trace
         (needed for allocating memory).
         Preset=the length of the first input trace.

FNO    - The first shot (or rp) to apply the mix to.  Shot (rp) numbers
         must increase monotonically.
         Preset=1

LNO    - The last shot (rp) number to apply the mix to.  LNO must be
         larger than FNO in each list and must increase list to list.
         Default=fno

IHDR   - The index of the 16 bit integer SEG-Y trace header value to mix.
         See the discussion of HEADER MIX above.  Remember that parameter
         TYPE is set to 4 by use of this parameter.
         e.g. ihdr 100
         Default = none

LHDR   - The index of the 32 bit integer SEG-Y trace header value to mix.
         See the discussion of HEADER MIX above.  Remember that parameter
         TYPE is set to 4 by use of this parameter.
         e.g. lhdr 50
         Default = none

HDR    - The index of the 32 bit floating point SEG-Y trace header value
         to mix.  See the discussion of HEADER MIX above.  Remember that
         parameter TYPE is set to 4 by use of this parameter.
         e.g. ihdr 100
         Default = none

END    - Terminates each parameter list.

Note *****
1) At least 2, but not more than 10 trace weights or 100 header weights,
   may be given.
2) Neither weight nor dip may be changed within a job.


Written and copyrighted by:
Paul Henkart, Scripps Institution of Oceanography, 11 March 1981
ALL RIGHTS RESERVED
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