PROCESS T2F
                                ------- ---

Parameters, alphabetically:
addwb    coords    etime     fftlen    fno       ftr      
lno      lprint    ltr       stime     window    winlen

Document Date: 1 October 2009
Updates:
        Oct. 2008 - Add coords AMPL

PROCESS T2F converts traces from the time domain to the frequency domain.
Each trace is windowed, padded with zeroes to a power of 2, transformed,
and optionally converted to polar coordinates.  Traces left in rect-
angular coordinates are in complex form such that the imaginary part of
each frequency immediately follows the real (real-imaginary pairs).

Traces in polar form have the amplitude spectrum in the first half of the
output trace while the wrapped phase spectrum is in the second half of 
the trace.

Each output trace will contain a power of 2 + 2 number of samples and is
the number of samples used in the FFT (fftlen+2).  There are fftlen/2+1
frequencies in the output trace representing frequencies 0 (dc) to the 
Nyquist frequency (1./(2*Sample interval)).

Any seismic process may be used on frequency data, but some post T2F 
processes may not make geophysical sense.  Frequency domain plots may be
made using polar coordinates and plotting the first half of the trace.

Bandpass filter and deconvolution should be done in the time domain using
processes filter and decon before the frequency domain processes.

A good review of the frequency domain is "A Guided Tour of the Fast
Fourier Transform" by G.D.Bergland in "IEEE Spectrum", July 1969.

THE PARAMETER DICTIONARY
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STIME  - Start time, in seconds, of the data to transform.  The use of
         stime causes the the deep water delay to be set to 0. and the
         first time sample on an inverse transform (PROCESS F2T) to be 0.
         Preset = the delay of the trace.  e.g.  stime 3.3

ETIME  - End time, in seconds, of the data to transform.  The data after
         etime will be padded with zeroes in order for the data length be
         a power of 2.
         Preset = the entire data trace.    e.g.  etime 4.0

ADDWB

WINDOW - The type of window to apply before computing the fft.
       = hamm, Hamming
       = hann, Hanning
       = bart, Bartlett (triangular)
       = rect, rectangular (box car - no window)
       = blac, Blackman
       = ebla, exact Blackman
       = blha, Blackman-Harris
        Preset=hamm  e.g. window rect

WINLEN - The window length, in seconds.  A window length of zero causes
         the entire time domain gate to be windowed.  A non zero length
         indicates that winlen data will be modified at both ends of each
         data gate.
         Preset=0  e.g.  winlen .2

COORDS - The coordinates of the output trace.
       = rect, rectangular coordinates.  The output trace will be complex.
         The trace values will consist of real and imaginary pairs.  The
         use of rectangular coordinates is slightly faster than polar 
         coordinates, and is understood by frequency domain processes 
         such as f2t.
       = polr, polar coordinates.  The first half of the output trace 
         will be the full (-pi to +pi) amplitude spectrum and the second 
         half of the trace will be the phase spectrum.
       = ampl, amplitude spectrum.  Only the positive portion ( 0 to pi )
         of the amplitude spectrum is output.
         Preset = rect   e.g.  coords polr

FFTLEN - The number of points to use in the FFT.  T2F will make this a 
         power of 2 if it is not.
         Preset = the number of points in the trace.  e.g. fftlen 1024

END    - Terminates each parameter list.

Written and copyrighted (c) by:
Paul Henkart, Scripps Institution of Oceanography, January 1984 
ALL RIGHTS RESERVED.