How to Get 1D Power Spectra from 2D FFT Image

Dear All,
  Sorry for bothering. 
  I had a 2D TEM image and I already used ImageJ to get a 2D power spectra. 
(FFT transform on the TEM image).
   The problem is: I wan to average the radial intensity distribution of all 
the direction on the 2D power spectra to get a 1D power spectra. That is to 
say, how to extract a 1D magnitude of the 2D transform. So, I am wondering is 
there such a plugin to average over the azimuthal angel to yield the radial 
power spectra?
   Thanks a lot and your respons will be well appreciated!
  Regards
  Ben

                
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