Abstract
The quality of an interferogram, which is limited by various phase noise, will greatly affect the further processes of InSAR, such as phase unwrapping. Interferometric SAR (InSAR) geophysical measurements’, such as height or displacement, phase filtering is therefore an essential step. In this work, an improved Goldstein interferogram filter is proposed to suppress the phase noise while preserving the fringe edges. First, the proposed adaptive filter step, performed before frequency estimation, is employed to improve the estimation accuracy. Subsequently, to preserve the fringe characteristics, the estimated fringe frequency in each fixed filtering patch is removed from the original noisy phase. Then, the residual phase is smoothed based on the modified Goldstein filter with its parameter alpha dependent on both the coherence map and the residual phase frequency. Finally, the filtered residual phase and the removed fringe frequency are combined to generate the filtered interferogram, with the loss of signal minimized while reducing the noise level. The effectiveness of the proposed method is verified by experimental results based on both simulated and real data.
Highlights
As an all-weather all-time remote sensing technique, the synthetic aperture radar (SAR) is of great importance in many fields, such as natural hazards’ monitoring, ocean investigation, geographic mapping, and so on [1,2,3]
To reduce the phase unwrapping difficulty and improve the precision of the unwrapped phase, phase filtering has become an essential step for Interferometric SAR (InSAR) data processing [14,15,16]
Since the estimated principal phase component is subtracted from the original noisy phase, the prefiltering operation improves the accuracy of fringe frequency estimation without reducing the resolution of the interferogram
Summary
As an all-weather all-time remote sensing technique, the synthetic aperture radar (SAR) is of great importance in many fields, such as natural hazards’ monitoring, ocean investigation, geographic mapping, and so on [1,2,3]. The traditional Goldstein filter, as a low-pass filtering method, smoothes the intensity of Fourier-transformed samples in overlapped interferogram patches [22] It is widely used for InSAR because of its notable noise suppression capability and fast operation [14]. Since the filter response in each overlapping window can be essentially considered as a low-pass filter, the high frequency components of fringes are suppressed [26] These methods may result in loss of fine details in an interferogram, especially in areas with dense fringes and complex textures.
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