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Comparison of Global and Local Approach to Phase Unwrapping for Rugged Terrain

Ludmila Zakharova(1)

(1) IRE RAS, Vvedensky sq., 1, 141190, Fryazino, Russian Federation

Abstract

The rugged topography of the scene is one of factors that cause trouble at the phase unwrapping stage of interferometric processing. All the phase unwrapping techniques may be divided on to classes: global and local ones with consequent specific distortions of unwrapped phase. In the given paper three phase unwrapping methods are under examination: least squares global method (D.C. Guillia and L.A. Romero, 1994), branch cut local method (R.M. Goldstein et al., 1988), and frequency analysis local method (A.I. Zakharov and P.V. Tugarinov, 2000). Some modifications of these methods are applied in order to improve the quality of solutions. Comparative analysis of unwrapped interferometric phase images was implemented in three aspects. Firstly, we estimate the statistical properties of the differences in solutions in spatial domain. Secondly, we analyze in spatial domain the types of distortions produced by the phase unwrapping methods under discussion. Thirdly, we analyze spectral properties of the solutions in spatial frequency domain in order to make conclusion about type of distortions and smoothing properties of methods. The experimental data we used were ERS-1/2 tandem data over Baikal Lake coast (Siberia) available under AO3-429 project. The topography of the scene is very diverse: it includes flat valleys, hills with moderate slopes, and steep mountain ridges. The interferometric coherence varies over the scene from perfect on unforested valleys to zero at the shadowing and layover (under-sampled) areas. Using different phase unwrapping algorithms we got the possibility to estimate the results of their performance for the regions of different interferogram quality, to show type and level of the unwrapped phase distortions and to work out recommendations on the selection of the approach with respect to the type of the surface cover.

 

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Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry