NAME

     fft3d - (Step 1 of 3) 3D V(z) Phase  Shift  Poststack  Depth
     Migration

SYNOPSIS

     [-Nntap] [-ff1] [-fcf2] [-FCf3] [-Ff4]  [-BRrec1]  [-ERrec2]
     [-PRrpad]  [-BTtrc1] [-ETtrc2] [-PTtpad] [-BSsmp1] [-ESsmp2]
     [-PSspad] [-DTMSdt] [-DXdx] [-DYdy] [-Mmbytes] [-2D] [-V]  [
     out=outfile]  [  data_path=path]  [ data_suffix=suffix] [-?]
     [-h]

DESCRIPTION

     fft3d is the first step of three steps to  perform  a  phase
     shift  depth  migration  on  a volume of data in coordinates
     (t,x,y).  fft3d performs a 3D  fft,  applies  a  trapezoidal
     filter  over  frequency  and  outputs  data  in  coordinates
     (w,kx,ky).  The input  time  data  is  typically  a  3D  CMP
     stacked dataset. Both the input and output are USP formatted
     datasets.

  Command line arguments
     -Nntap
          Enter the input dataset name after typing -N.

     -ff1 This value is the lower cut-off frequency of  the  tra-
          pezoidal  filter  to be applied to the input data.  The
          default is 0.

     -fcf2
          This value is the lower corner frequency  of  the  tra-
          pezoidal  filter  to  be applied to the input data. The
          default is f1.

     -FCf3
          This value is the upper corner frequency  of  the  tra-
          pezoidal  filter  to  be applied to the input data. The
          default is f4.

     -Ff4 This value is the lower cut-off frequency of  the  tra-
          pezoidal  filter  to  be applied to the input data. The
          default is nyquist-1.

     -BRrec1
          This value is the  starting  record  to  use  from  the
          input.  The default is 1.

     -ERrec2
          This value is the ending record to use from the  input.
          The default is to use all the records.

     -PRrpad
          This value specifies how many zero records to pad.  The
          default is 0.

     -BTtrc1
          This value specifies the first trace  to  use  of  each
          input record. The default is 1.

     -ETtrc2
          This value specifies the last  trace  to  use  of  each
          input record.  The default is to use all the traces.

     -PTtpad
          This value specifies the number of zero traces  to  pad
          at the end of each input record. The default is 0.

     -BSsmp1
          This value specifies the first sample to use from  each
          trace. The default is 1.

     -ESsmp2
          This value specifies the last sample to use  from  each
          trace. The default is to use all of the samples.

     -PSspad
          This value specifies the number of zero samples to  pad
          to each trace of the input.  The default is 0.

     -DTMSdt
          This command line argument  is  used  to  override  the
          value  in the input line header.  The default is to use
          the value in the line header if it is correct.

     -DXdx
          This value represents the input dataset  trace  spacing
          in  feet  or  meters.  The  default  is to use the line
          header value 'Dx1000'.

     -DYdy
          This value represents the input dataset record  spacing
          in  feet  or  meters.  The  default  is to use the line
          header value 'Dy1000'.

     -Mmbytes
          This value represents the number of megabytes of memory
          the  program  can  use  for  temporary work space.  The
          default is 64 megabytes for Crays and 32 for all  other
          architectures.

     -2D  If this value is present on the command line,  the  fft
          will be performed only on the first 2 dimensions of the
          input.


      out=outfile
          Enter the basename of the output dataset  after  typing
          out=. fft3d creates two files, a dictionary file giving
          some basic information about the seismic data, and  the
          seismic   data.  The  dictionary  file  will  be  named
          `basename`.fft3d,  and  the  seismic   data   will   be
          `basename`.fft3d.usp.  This dataset will be in the out-
          put of the 3D fft as described above.  The  coordinates
          will be (w, kx, ky).

      data_path=path
          This is the full path name to the directory  where  you
          want the output to be written.  There is no default.

      data_suffix=suffix
          This is the third  part  of  the  name  of  the  output
          dataset  as  explained  under  "out="  parameter.   The
          default is "usp" as shown above.

     -V   Enter -V for a verbose printout.

     -h   Enter -h for online help. The  program  will  terminate
          after printing this.

     -?   Enter -? for online help. The  program  will  terminate
          after printing this.

SEE ALSO

     mbs, dspace, 3dvzmig, cmmvz3d, zkk2zxy

BUGS

     None known.

AUTHOR

     N. D. Whitmore, Jr., Ron D. Coleman

COPYRIGHT

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