NATIONAL AND KAPODISTRIAN UNIVERSITY OF ATHENSNATIONAL AND KAPODISTRIAN UNIVERSITY OF ATHENS
LABORATORY OF REMOTE SENSING

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RADAR INTERFEROMETRY

Differential interferometry (InSAR) is a technique that can be used for the detection of crustal deformation using suitable pairs of SAR images.

Current activites

Conventional InSAR
Conventional InSAR can deliver spectacular measurements of the large-scale ground deformations associated with main earthquake events, volcano deformation, landaslides etc (Massonnet and Rabaute 1993, Zebker et al., 1994, Wright et al., 2001), provided the temporal separation and horizontal baseline between the two SAR scenes used are kept within appropriate limits. Many examples exist and such results on their own offer unique input to strain models and support the understanding of fault mechanisms and volcanic deformation modelling and have even been successfully used for the verification of insurance claims. Though usually applicable to the main co-seismic event, and so is perhaps a 'response' technique, the deformation information can provide valuable understanding of fault mechanisms and thus input to forecast models in the mitigation phase. However, conventional InSAR is not considered a tool for the measurement of the millimetre-scale motions associated with interseismic activity; the displacement resolution of the technique becomes degraded by temporal decorrelation and/or atmospheric heterogeneity resulting in phase ambiguites of similar orders of magnitude as the ground displacements anticipated.

PS InSAR
Permanent Scatterer InSAR technique (Ferretti et al., 1999) involves the processing of more than 30 interferograms over the same place to identify a network of temporally-stable, highly reflective ground features – permanent scatterers. The phase history of each scatterer is then extracted to provide interpolated maps of average annual ground motions, or more importantly, the motion history, up to 9 years (length of SAR data archive), of each individual scatterer, thus providing a 'virtual' GPS network with 'instant' history. Due to the relatively high density of scatterers that occur in built environments (a few hundred per square kilometre) and the large number of atmosphere samples (SAR scenes) used, the heterogeneity of the atmosphere can be accurately modelled so that measurements of sub-millimetre accuracy can be calculated. A limitation of PSInSAR is the lack of control over precise scatterer location, but with the densities obtained in built environments this is not considered an issue for the mapping of interseismic ground motions.

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