Improved InSAR Phase Noise Filter in Frequency Domain

Abstract

The Goldstein filter is the commonly used filter for interferometric synthetic aperture radar (InSAR) phase noise reduction, and its performance is determined by three parameters: the power spectrum filtering parameter α, the patch size of the InSAR phase, and the smoothing window on the power spectrum. However, the noise level of the different regions in an interferogram changes greatly due to the terrain topography. The InSAR phase will be overfiltered in high-coherence regions and be underfiltered with high noise level in low-coherence regions if the unchangeable processing parameters are used. In this paper, we propose an improved InSAR phase filter in frequency domain. First, we use different window sizes to suppress the phase noise, and the window size is determined by the coherence of the central processing pixel. A pixel with higher coherence uses a smaller filtering window size and vice versa. Second, the samples in the filtering window are not independent and identically distributed samples for the terrain topography. To deal with this problem, we use fringe frequency compensation to eliminate the effect of the terrain topography. Third, combining with a newly defined filtering parameter α, we execute the phase filtering procedure pixel by pixel, which is different from the Goldstein filters. Furthermore, we use the Fourier transformation of a small window (generally 3 × 3) to deal with the power spectrum of the InSAR phase patches. Compared with other improved Goldstein filters and spatial-based filters, the effectiveness of the newly improved InSAR phase noise reduction method in frequency domain is investigated by both simulated and real data sets.