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Effects of baselines on InSAR coherence: applications to earthquake damage detection

Marco Chini(1), Nazzareno Pierdicca(2), Luca Pulvirenti(2), Christian Bignami(3) and Salvatore Stramondo(3)

(1) Univ. “Alma Mater Studiorum” of Bologna, Viale C. Berti Pichat 8, 40127 - Bologna, Italy
(2) “Sapienza” Univ. of Rome, Via Eudossiana 18, 00184 - Rome, Italy
(3) Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143 - Rome, Italy

Abstract

Remote sensing techniques have revealed a suitable monitoring tool to provide data useful for disaster studies. They allow the quick detection of damages and building collapses due to earthquakes, especially in remote areas or where the infrastructures are not well developed to ensure the necessary communication exchanges. The exploitation of InSAR complex coherence sensitive to changes in the spatial arrangements of the scatterers has been proved useful to detect urban damages due to an earthquake. The interaction of the SAR signal with the urban structures has been studied in papers available in the literature. These highlight that the radar return from urban settlements is determined mainly by the double bounce mechanism. However, diffraction effects from the structure edges, as well as trihedral reflections also, contribute to the radar echo. Further developments are needed in the field of the analysis of SAR images in urban areas to completely define the characteristics of the electromagnetic response of buildings and the influence of urban settlements characteristics on the backscattered signal. In particular, a better evaluation of the influence of scatterers (i.e. buildings) dimension and their distribution in the resolution cell is needed to understand and explain the role of the SAR acquisition geometry on InSAR phase coherence changes. InSAR phase coherence and intensity correlation of multilook images collected before and after the earthquake have been used in previous works to detect changes in built-up area. The decrease in complex coherence has been found very much dependent on the spatial and temporal baselines of the interferometric pair, which are not constant between the pre- and co-seismic pairs. In these paper a series of SAR images of Rome have been used to analyze these characteristics, in order to evaluate the potential and the limitation of InSAR techniques to detect urban changes for different values of baselines, both spatial and temporal. The effect of the baselines has been evaluated experimentally from the available ERS1/ERS2 images dataset. The drop-off of the InSAR phase coherence with the spatial baseline has been shown dependent on different urban texture which has been deduced by optical images. Am empirical model to correct for the effect of baseline an estimator of the urban damage level is proposed.

 

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