Interferogram phase noise filter using nonlinear anisotropic diffusion equation

The phase noise suppression methods applied on the interferogram of Interferometric synthetic aperture radar (InSAR) are studied. Filtering phase noise in an interferogram is an important aspect in InSAR data processing. But any improper altering of the wrapped phase may influence the quality of derived DEM because the interferometric phase contains the topographic information. Therefore, one of the difficulties in phase noise filtering is how to remove the noise and preserve the spatial resolution effectively. In this paper, a new adaptive approach based on the nonlinear anisotropic diffusion equation is presented for removing the noise in the interferogram. The key idea is that for low gradients, isotropic smoothing is performed, and for high gradient, smoothing is only applied in the direction of the isophote and not across it. During the course of noise suppressing, image features and their directions are extracted. Less smoothing is in the locations with strong image feature, and more smoothing in the locations with weak image feature; minimal smoothing in the directions across the image features, and maximal smoothing in the directions along the image features. At the end of this paper, this approach is compared with some existing approachs for InSAR noise filtering and the experimental results by processing Canada Radarsat1 data are used to confirm that the method is more effective in suppressing noise in the interferogram.