| Summary: | Synthetic aperture radar (SAR) interferometry is a technique for obtaining accurate elevation
maps of the Earth from radar images. Local fringe frequency estimates are needed in several
stages of the interferometry process. They are used to correct the effect of the topographic slope
in the estimation of the interferogram coherence. They are needed to define the frequency center
for adaptive band-pass filtering or to model the local phase in slope-correction filtering. Finally,
accurate fringe frequency estimates facilitate the phase unwrapping process.
In this work, I propose a new algorithm for local fringe frequency estimation in which the
SAR interferogram signal is pre-filtered before the local frequency estimation is performed. This
allows the use of a simpler and more efficient frequency estimator that operates at the pixel level.
The proposed scheme shows advantages over other schemes because it achieves a better spacefrequency
resolution and therefore tracks the topographic changes of the scene more accurately.
The filters used in this work are modulated Gaussian functions with variable spatial aperture and
bandwidth. In this way, the analysis window is adapted to the local characteristics of the signal
at all samples. The variable-aperture filters are similar to the variable space-frequency domain
filters used in wavelet analysis. I present results for synthetic and real SAR interferograms, as
well as the performance of the proposed algorithm.
An application of the frequency estimation method is developed for the noise filtering stage.
A non-linear phase model is built to locally flatten the phase allowing the averaging of a higher
number of samples without significant distortion. Simulations show that this alternative method
achieves a better performance than two other reported methods when the interferogram
coherence is moderately high. However, the alternative method does not solve the problem of
phase discontinuities in the presence of topographically induced residues. === Applied Science, Faculty of === Electrical and Computer Engineering, Department of === Graduate
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