Measuring subsidence in the centre of Lisbon with persistent scatterers interferometry (PSI), CGPS and leveling surveys

Abstract

Land subsidence was detected for the first time in the city of Lisbon in 2004 (and confirmed in 2006), in the scope of GMES-Terrafirma project, through the analysis of ERS and ENVISAT ASAR interferometry time-series [1] [3]. The region affected is partially bounded by mapped geological faults, and extends over an area of ~4 Km2. Here we extend the PSI monitoring of this area until the end of 2010, using 67 ENVISAT ASAR and ERS Single Look Complex images, acquired from two separate orbits (ascending and descending geometries). The processing is done with the SARscape Persistent Scatterers module. We compare our results with previous PSI maps produced by the GMES Terrafirma service, and with ground-truth data, namely (1) levelling surveys crossing the subsidence region, and (2) CGPS time-series. We further investigate two possible causes for the ground deformation observed: surface deposits compaction due to increased urbanization, or compaction of deep low permeability clay layers due to groundwater withdrawal.