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Coherence Decomposition Analysis

Teng Wang(1,2), Daniele Perissin(2), Mingsheng Liao(1), Lijun Lu(1) and Fabio Rocca(2)

(1) Wuhan University, P.O. Box C310, 129# Luoyu Road, 430079 Wuhan, China
(2) Politecnico di Milano, Via Giuseppe Ponzio, 34/5, 20133 Milan, Italy


Coherence information from SAR interferometry is very useful in many applications, such as image classification, target detection, etc. The coherence magnitude can be estimated over a window by spatial averages. It is well know that the value of coherence contains different kinds of information, which are mainly caused by spatial and temporal de-correlation. Take advantage of geometry relationship between two acquisitions and bandwidth of the SAR system, one can get the value of spatial de-correlation. After removing the spatial part, temporal de-correlation can be obtained to indicate the physical changes between acquisition times in the illustrated terrain.

However, in the areas with steep terrain, the spatial de-correlation is not simply caused by the difference in the incidence angles between the two acquisitions, the local slope of every pixel also affect the coherence values. If this part of de-correlation is not considered, the temporal de-correlation from coherence decomposition will not give accuracy information of physical changes of the terrain.

In order to overcome this problem, we divide the factors of spatial de-correlation into 2 parts: 1, the wavenumber shift caused by incidence angles difference; 2, volume de-correlation, including the vegetables thickness and terrain variation in a resolution cell. The SRTM DEM is used to obtain the local slope of the SAR image firstly. Then, pre-filtering procedures are performed in azimuth and range direction to remove the non-overlap part of the spectrums. And, a coherence model is applied on different pairs of ERS images in mountainous areas with different temporal baselines to decompose the coherence. Finally, the coherence decomposition results are analyzed.


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