Application of PSI technique to landslide investigations in the Caramanico area (Italy): lessons learnt
Janusz Wasowski(1) , Fabio Bovenga(2)
, Raffaele Nutricato(2)
, and Alberto Refice(3)
CNR-IRPI, Bari ,
Via Amendola 122 I,
(2) Dip. Interateneo di Fisica - Bari, Via Amendola, 173, 70126, Bari, Italy
(3) CNR-ISSIA, Bari, Via Amendola 122/d, 70126, Bari, Italy
Landslides and unstable slopes very often occur in settings that are unfavourable for the application of standard multi-temporal DInSAR PSI techniques. This is the case of the Caramanico area, located in a narrow Apennine valley bordered by high mountains, characterised by a relatively high precipitation and rich vegetation, as well as by complex microclimate. Under such conditions the influence of atmospheric heterogeneities (changes in tropospheric water vapour concentrations) on the DInSAR results may be particularly significant. Furthermore, the high-relief, steep and irregular topography may introduce errors in the interferometric pre-processing, making the joint estimation of displacements and DEM errors more difficult.
Indeed, the preliminary application of standard multi-temporal DInSAR PSI techniques to the Caramanico area posed considerable problems linked to the low density of PS . The application of a refined PSI approach , together with an alternative, classification-based PS candidate detection method , allowed to obtain PS maps with more stable targets and higher average inter-image coherence, and thus a lower probability of detecting false displacements.
Although the harsh conditions encountered in Caramanico confer some uncertainty to the exact significance of the SAR target displacement results, the spatial distribution of moving PS is not random. The reliability of the SAR interferometry results is supported by the fact that spatially limited groups of PS, exibiting the same LOS deformation behaviour can be clearly recognised. Furthermore, the locations of the groups of moving PS appear consistent with the areal distribution of recent and past landslide activity in Caramanico. The PS groups also tend to coincide with places including distressed buildings and retaining structures.
In general, however, some variability in the local ground surface displacement patterns is to be expected in man-modified, geologically and geomorphologically complex hillslope settings like that of the Caramanico area. The variability may be related not only to landslide processes but also to other more or less local ground deformation phenomena such as subsidence (whether natural or man-made), settlement of engineering structures, volumetric changes of clay-rich materials. It follows that in situ data and monitoring controls will usually be needed to discriminate the exact cause of ground surface deformations detected on the basis of PS analysis.
The ERS images were provided by the European Space Agency under ENVISAT AO-313 project. This work was supported in part by the European Community (Contract No. EVGI 2001-00055 - Project LEWIS) and by the Italian Space Agency (ASI) projects (Contracts No. I/R/27/00 and I/R/073/01).
 J. Wasowski, F. Bovenga, R. Nutricato, A. Refice, “Test of applicability of Permanent Scatterers technique to landslide investigations in peri-urban areas”, Proceedings of FRINGE’03 ESA-ESRIN Workshop, Frascati (Roma), Dicembre 2003. (http://earth.esa.int/fringe03/)
 F. Bovenga, A. Refice, R. Nutricato, L. Guerriero, M.T. Chiaradia, “SPINUA: a flexible processing chain for ERS / ENVISAT long term interferometry”, Proceedings of ESA-ENVISAT Symposium 2004, 6-10 September, 2004, Saltzburg, Austria.
 A. Refice, F. Bovenga, R. Nutricato, M.T. Chiaradia, J. Wasowski, “Land-cover classification-based Persistent Scatterers identification for peri-urban applications”, Proc. IGARSS’05, Seoul, Korea, 25-29 July 2005.