NAME

     bkgrnd - compute and apply very low frequency  gain  correc-
     tion to trace data

SYNOPSIS

     bkgrnd [ -Nntap ]  [  -Ootap  ]  [  -rsrs  ]  [  -rere  ]  [
     -sanalysis  start  ]  [  -eanalysis  end  ]  [  -mdmode  ] [
     -mdesired slope ] [ -V ] [ -? ] [ -H ]

DESCRIPTION

     BKGRND identifies and compensates for amplitude  decay  (may
     be  either  positive  or  negative)  in  trace data which is
     slowly varying with offset , on  a  record-by-record  basis.
     The  amplitude  variation  is  measured  by computing a mean
     (arithmetic, RMS, geometric) or  median  absolute  amplitude
     over a (user-defined) large time window of each trace in the
     record, assuming the  amplitude  variation  is  linear,  and
     finding the slope and intercept of that variation. The meas-
     ured decay is removed and an arbitrary new decay imposed  on
     each  data  sample by adding and subtracting the current and
     desired linear trends from the data according to

      y' = y + (trace number -1) * (M2 - M1)

     where y' is the output amplitude,  y is the input amplitude,
     M2  is  the desired slope of the linear decay, and M1 is the
     current slope.

     By using a large time window, the effects of  normal  trace-
     to-trace variation expected for individual reflection events
     (either increasing or  decreasing)  is  minimized.   If  the
     "background"  variation  does  exist,  a non-zero slope term
     will be found and the decay compensated for.

     bkgrnd gets both its data and its  parameters  from  command
     line arguments.  These arguments specify the input and  out-
     put data set names, temporal and spatial window  parameters,
     averaging method, and desired output slope.

  Command line arguments
     -Nntap
          Enter the input data set name or file immediately after
          typing  -N;  entering  nothing  specifies a stdin pipe.
          This input put file should include  the  complete  path
          name  if the file resides in a directory other than the
          one  from  which  you  start  the  program.    Example:
          -N/work_area/dummy  tells  the program to look for file
          "dummy" in directory "work_area".

     -Ootap
          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).

     -rsrs
          (integer)  First  (sequential)   record   to   process.
          Default = 1 (the first).

     -rere
          (integer) Last (sequential) record to process.  Default
          = process all.

     -sanalysis start
          Enter the start time, in ms, for the window over  which
          the  average  of  absolute  values  will be determined.
          (Default = 0)

     -eanalysis end
          Enter the end time, in ms, for the end time of the win-
          dow  over  which the average of absolute values will be
          determined. (Default = end of trace)

     -mdmode
          Enter the value which specifies the type of gain compu-
          tation  desired.  Valid values are "0" for AAA, "1" for
          RMS, "2" for GMAA, and "3" for median.  Default = 0.

     -mdesired slope
          Enter the desired slope  of  the  linear  variation  of
          average  amplitude  as funtion of offset (trace number)
          as a floating point value.  You may  want  to  run  the
          program  with  the  verbose mode turned on first to see
          typical values of the current slope.

     -V   Enter the command line argument '-V' to printing to the
          screen  of  the  slope  and intercept computed for each
          record as well as parameter information to the standard
          sysout file.

     -?   Enter this (or '-?' if you are running in  c-shell)  to
          get  online  help.   The  program  will terminate after
          printing this.

     -H   Enter this to get online help.  The program  will  ter-
          minate after printing this.

BUGS

     Unknown

AUTHOR

     Richard Crider, Houston x7070