FINDINGS OF PERSISTENT SCATTERER INTERFEROMETRY (PSI) FOR VILNIUS AREA, LITHUANIA

Ground surface deformations can be related to natural and anthropogenic activities. The availability of ground movement data from regular satellite observations, combined with the knowledge of local geology and geomorphology, can help to improve our understanding of subsidence and soil geotechnical settlement phenomena, as well as to distinguish them from structural deterioration of buildings, which in urban environments represent the most common type of radar targets (PS). In Lithuania ground surface deformations are usually related to landslides, karstic, suffusion processes and anthropogenic activities (particularly in urban areas), which can trigger destruction of buildings, communication lifelines and soil consolidation. This paper is intended to illustrate considerable interpretative difficulties concerning the Persistent Scatterers Interferometry (PSI) results from synthetic aperture radar (SAR) data acquired over the Vilnius area (Lithuania) in the framework of TERRAFIRMA project. Protection of groundwater from pollution in the face of both man's intervention and geologically-driven movements is a high priority for the City Authorities. The distribution of numerous PS shows evidence of the spatial variability of the ground conditions throughout the old town and adjacent area of Vilnius. PS detected in the centre of Vilnius are characterized by velocities mainly ranging between -1.5 to + 1.5 mm/year during about 8.5 years of observation. These figures are within the measurement precision error and imply a general stability of the city centre. Nevertheless, the review of the PS dataset has enabled to identify several sites within the Vilnius area characterized by spatially consistent concentrations of the downward moving PS. The localities as well as the site of the PS reference point were checked during the field reconnaissance and the implications of PS results are discussed in this paper.