Abstract
Abstract. In this paper, we studied and tested different filtering approaches of the SAR interferograms in the spatial and wavelet domains. In the spatial domain, we applied the classic Lee filter and the Weighted Median Filter WMF. In the wavelet domain, we tested a noise reduction algorithm WInP proposed by López and Fàbregàs and its enhanced version FAMM developed by Abdelfattah and Bouzid. Those filters are validated with different SAR interferograms provided by Radarsat-2, Envisat, ERS-2 and COSMO-SkyMed SLC data acquired over regions of Mahdia and Ben Guerden in Tunisia. The aim of this study is to select the optimal filtering approach with respect to the fringe pattern in the interferogram. This selection is based on the Digital Elevation Model error computed between the filtered unwrapping phase image and the Global ASTER DEM of the same regions and verified with simulated interferograms.
Highlights
Interferometric Synthetic Aperture Radar (InSAR) is a technique used to measure the relief and detect any changes accrued to the surface of the earth by calculating the phase difference information between two complex radar images (Abdelfattah and Nicolas, 2002),(Goldestein et al, 1988)
We consider that the filtered interferogram is well adapted to the unwrapping process if it respect the edges of the interferometric fringes and filter the homogeneous zones and it is clear that the filters operated in the wavelet domain (WInPF and FAMM) give better results than the spatial filters (Lee and WM filters)
The two filters in main should be used. This statement can be explained by the fact spatial domain (Lee and WMF), which are based on the compute that the WInP and the FAMM filters use the Discrete Packet Wavelet Transform (DPWT) with three deof mean values, smooth the image by using the noisy and useful composition levels
Summary
Interferometric Synthetic Aperture Radar (InSAR) is a technique used to measure the relief and detect any changes accrued to the surface of the earth by calculating the phase difference information between two complex radar images (Abdelfattah and Nicolas, 2002),(Goldestein et al, 1988). A phase difference image is generated using both complex images, which is named interferogram. Xie et al (Xie and Pi, 2011) uses the unscented Kalman filter that allow the noise filtering and the phase unwrapping simultaneously. They are not adapted to noises with local variations. As an alternative to overcome this drawback, the filters that use an average process and which require a locally phase unwrapping and rewrapping step, in order to preserve phase discontinuities, are more adapted to SAR interferogram noise problem. The noise reduction operation is commonly applied before phase unwrapping process (Huot et al, 1998)
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