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Baseline combination for InSAR DEM atimetric resolution enhancement

Dominique Derauw(1) and Anne Orban(1)

(1) Centre Spatial de Liege, Avenue du Pre Aily, 4031 Angleur, Belgium


Combination of several interferograms of a same area, each having its own ambiguity of altitude, allows producing a combined interferogram with either a better signal to noise ratio or a lower ambiguity of altitude, unreachable from a single interferometric pair. Baseline combination by averaging can only be applied on unwrapped phases. Therefore, each interferogram must be unwrapped prior to combination. We thus implemented a three step phase unwrapping procedure allowing to take fully advantage of an interferometric data set containing several InSAR pairs of a given site. In the first step, the best interferogram of the set is unwrapped classically to generate a first phase approximation. The second step consists in flattening all the other interferograms and to unwrap a filtered version of them. The third step consists in adding both components with the residual phase issued from the difference between the flattened interferogram and the filtered version of itself. Phase averaging allows to lower substantially the phase standard deviation and thus to increase the altitude accuracy. InSAR baseline combination by summation allows reaching peculiar equivalent baselines while raising signal to noise ratio in the resulting interferogram. Despite this drawback such combination revealed to be highly useful in atmospheric artifacts identification and localization. Choosing adequately the interferograms to combine allow to generate interferograms with very short baseline in which the topographic phase component can be neglected, revealing artifacts before going further in a then useless processing. Baseline combination process was developed in the frame of a DUP project. An example of baseline combination usefulness is given using five Tandem pairs of the area of Brussels, Belgium.


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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