Hi Everybody,
I extracted canopy height model using interferometric technic and TanDEM-X data, after making interferogram step, I did Goldstein filtering in snap software. 
I have tried several window ( 33, 55, 7*7) and FFT sizes and (32, 64, 128, 256 ). my final result was good for 32 FFT size. I don’t know what is mean of FFT size and what difference is with window size.
FFT stands for fast Fourier transform. Basically, small sample patches of the interferogram are transformed into a 2D representation and filtered in this domain, thus making the filter parameter flexible [0-1] for regions of different noise levels.
Richard Goldstein published a paper on this filter technique. It however doesn’t explicitly mention the role of FFT for the filtering:
Goldstein & Werner (1998): Radar interferogram filtering for geophysical applications
Better explanations are given in papers adapting his idea:
- Baran et al. (2003): A modification to the Goldstein radar interferogram filter
- Li et al. (2007):Filtering method for SAR interferograms with strong noise
- Li et al. (2008): Improved filtering parameter determination for the Goldstein radar interferogram filter
- Tian et al. (2018): Bias Removal for Goldstein Filtering Power Using a Second Kind Statistical Coherence Estimator
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