NAME

     princomp  - noise analysis/reduction  using  principal  com-
     ponents

SYNOPSIS

     princomp [ -Nntap ] [ -Ootap ] [ -Ssfile ]  [  -nsnstr  ]  [
     -nenetr  ] [ -rsnrst ] [ -renred ] [ -ibibiggest ] [ -irirec
     ] [ -epctoteng ] [ -kdkodepc ] [ -I ] [ -V ] [ -? ]

DESCRIPTION

     princomp decomposes seismic data (pre- or post  stack)  into
     eigenvalues  and  eigenvectors  in  an  analogous  manner to
     Fourier spectra.  The eigenvectors are in some  way  related
     to  the  dip  components  in  the  data  and the eigenvalues
     represent the strengths of these components.  The  aim  here
     is to represent the data with as few eigenvalues as possible
     and in such a way as to enhance the desired features in  the
     data (e.g. reducing random noise; enhancing flat dip). As an
     analysis tools an option is provided to output the %  energy
     reconstruction  as  a function of the numbers of eigenvalues
     which can then be plotted using xgraph.

     The two basic methods of filtering using this program are:

     1) by choosing either the first N largest eigenvalues  which
     will describe the major features of the data, or by specify-
     ing that the eigen-reconstruction of the data reach  some  %
     of  the  original  energy  in the input data (another way of
     taking the most important eigenvectors), or

     2) by specifying a code  which  will  exclude  (or  include)
     specific  eigenvectors  from  the  reconstruction.  Here you
     have to tediously experiment until you get the code you want
     but sometimes this can be rewarding by finding a combination
     that enhances just the right features in the data.

     When applying princomp to pre-stack data it is a  good  idea
     to  try  to  flatten some series of events (e.g. either pri-
     maries or multiples).  This is especially true if the events
     you are going to flatten are relatively strong in amplitude.
     In this situation the first few eigenvalues will  be  enough
     to adequately describe the flat portion of the record.

     princomp gets both its data and its parameters from  command
     line  arguments.  These arguments specify the input, output,
     the start and end traces, the start and end records, and the
     filtering  methods.   Only  the  data  between the trace and
     record limits will be processed; the rest of the  data  will
     be  passed  through  unchanged.   Several different princomp
     runs  each  with  different  parameters  and  with  mutually
     exclusive  trace  and record limits can be piped together to
     effect a "spatial" princomp.

  Command line arguments
     -N ntap
          Enter the input data set name or file immediately after
          typing -N unless the input is from a pipe in which case
          the -N entry must be omitted.  This input  file  should
          include the complete path name if the file resides in a
          different directory.  Example -N/b/vsp/dummy tells  the
          program to look for file 'dummy' in directory '/b/vsp'.

     -O otap
          Enter the output data  set  name  or  file  immediately
          after typing -O.  This output file is not required when
          piping the output to another process.  The output  data
          set also requires the full path name (see above).

     -S sfile
          Enter the file name for the number of eiegenvalues vs %
          energy reconstruction which can then be displayed using
          xgraph:  xgraph < [file name]

     -ns nstr
          Enter the start process trace number.  The  default  is
          the first trace of the record.

     -ne netr
          Enter the end process trace number. The default is  the
          last trace of the record. Note: data outside the limits
          -ns, -ne will be passed unchanged.

     -rs nrst
          Enter start process record number.   Default  value  is
          the first record.

     -re nred
          Enter end process record number.  Default value is last
          record.  Note: data outside the limits -rs, -re will be
          passed unchanged.

     -ib ibiggest
          Enter the number of largest eigenvalues upon  which  to
          reconstruct.  This  can  sometimes  be  determined from
          plotting  the  -S[]  file  results  using  xgraph.   By
          observing  the point at which the curve flattens one is
          able to determine the number of eigenvalues required to
          accurately  reconstruct  most  sensible  data features.
          For instance if the file name is sout then the  command
          line to plot is

          xgraph < sout

     -epc toteng
          Enter % energy reconstruction  (the  actual  number  of
          eiegnvalues  will be determined internally).  Default =
          100

     -kd kodepc
          Enter binary code describing the actual eigenvalues  to
          be  excluded/included  from  the  reconstruction.   For
          those not familiar with binary code representation here
          are  some examples: for the 1st principal component use
          -kd2 (2**1); the 2nd component use -kd4 (2**2); 3rd use
          -kd8  (2**3);  exclude  1st  and  2nd  use -kd6 (2**2 +
          2**1); 1st, 2nd, and 3rd  use  -kd14  (2**3  +  2**2  +
          2**1).  As you can see the order of the component to be
          excluded is actually the  exponent  of  a  power  of  2
          number.   You can get the rest by extrapolation. See -I
          option below.

     -ir irec
          Enter the record interval for churning out  diagnostics
          including the xgraph file

     -norm
          Enter the command line argument  '-norm'  to  normalize
          traces  according  to  their average absolute amplitude
          before processing.  After  processing  the  scaling  is
          undone.  Note:  scale  calculation  is done using whole
          trace

     -rms Enter the command line  argument  '-rms'  to  normalize
          traces  according to their average rms amplitude before
          processing.  After processing the  scaling  is  indone.
          Note: scale calculation is done using whole trace

     -I   Enter the command line argument '-I' to include princi-
          pal components specified by the -kd[] entry above; oth-
          erwise these principal components will be excluded.

     -V   Enter the command line argument '-V' to get  additional
          printout.

     -?   Enter the command line  argument  '-?'  to  get  online
          help.  The  program terminates after the help screen is
          printed.

BUGS

     unknown

AUTHOR

     Original code by Bill Done; stripped down  version  by  Paul
     Gutowski

COPYRIGHT

     copyright 2001, Amoco Production Company
               All Rights Reserved
          an affiliate of BP America Inc.