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=3.571428You will notice that the setting for the trace id (trid) is 11. Typing:
% sukeyword trid ... 11 = Fourier transformed - unpacked Nyquist xr,xi,...,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.