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A New Method for Baseline Calibration in SAR Interferometry

Mario Costantini(1) and G Schiavon(2)

(1) Telespazio S.p.A, Via Tiburtina, 965, 00156 Rome, Italy
(2) University Tor Vergata, Via del politecnico,1, 00133 Rome, Italy

Abstract

Synthetic aperture radar (SAR) interferometry is based on the concept of observing the same scene with two slightly different radar trajectories. It results that each point of the scene is seen from two different positions along the two radar trajectories, and the differences between those points constitute the interferometric baseline. For quantitative SAR interferometry and differential interferometry applications, e.g. building digital elevation models (DEMs) or monitoring terrain displacement, baseline must be known with a higher accuracy than generally achievable from satellite or airplane trajectories or attitude measurements. Therefore, the nominal baseline is usually calibrated (i.e. corrected) by using a priori information, like ground control points. Traditional techniques for baseline calibration minimize the deviation between the measured unwrapped interferometric phase and reference values of it obtained from ground control points through a phase model depending on some baseline parameters. This approach requires the knowledge of unwrapped phase values. In this work a new method for baseline calibration is proposed, based on the idea of minimizing the deviation between the complex interferogram and a model of it, thus not requiring to unwrap the phase. The main advantage is that baseline calibration is not affected by possible phase unwrapping errors. In addition, if necessary for the successive processing, phase unwrapping is facilitated by a better phase flattening possible after baseline calibration. The function to be minimized in the proposed approach is not convex, which requires a global minimization strategy, in order to avoid to fall on local minima. This makes the method more complex and computationally demanding than the traditional technique. Tests performed both on simulated and real images confirm the validity of the proposed approach and show that requested computational time is comparable with that of other processing steps of SAR interferometry, and therefore completely acceptable in that context

 

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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