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1D Fourier Transforms

The program ``sufft'' produces the output of the Fourier transform operation as a complex data type. The program ``suifft'' is designed to accept complex input as would be generated by sufft to perform the inverse Fourier transform. The cascade of these operations is not quite an non-operation, because there is zeropadding which is automatically implemented for the transforms. Also, the header fields will not quite be right for seismic data. For example, try:

% suplane | suxwigb title="Original Data"  &
% suplane | sufft | suifft | sushw key=d1,dt a=0,4000 | suxwigb  &
The result is the same as the input, except there are more samples on the traces due to zero-padding required for the transform.

To view the amplitude and phase spectra, and the real and imaginary parts of the of the output of sufft, do the following

% suplane | sufft | suamp mode=amp | suxwigb title="amplitude" &
% suplane | sufft | suamp mode=phase | suxwigb title="phases" &
% suplane | sufft | suamp mode=real | suxwigb title="real" &
% suplane | sufft | suamp mode=imag | suxwigb title="imaginary" &
SU data has a format which allows for the storage of the real and imaginary parts of data in a complex datatype. To see the header field settings for that format, type:
% suplane | sufft | surange
sufft: d1=3.571428
32 traces:
 tracl=(1,32)  tracr=(1,32)  trid=11 offset=400 ns=72
 dt=4000 d1=3.571428
You will notice that the setting for the trace id (trid) is 11. Typing:
% sukeyword trid
...
                        11 = Fourier transformed - unpacked Nyquist
                             xr[0],xi[0],...,xr[N/2],xi[N/2]   
...
shows that trid=11 how the data are arranged in the output of the fft.

Of course, most of the time, we only want to have a quick look at the amplitude spectrum of a seismic trace, or a panel of seismic traces. For these purposes use ``suspecfx''

% suplane | suspecfx | suximage title="F-X Amplitude Spectrum"  &
which directly displays the amplitude spectra of each trace of the input SU data.


next up previous contents
Next: 2D Fourier Transforms Up: Transform and Filtering Operations Previous: Fourier Transform Operations   Contents
John Stockwell 2007-04-10