Assessing short- and long-time displacements in the Venice coastland by synthetic aperture radar interferometric point target analysis

The Venice Lagoon in Italy is a unique environment vulnerable to loss in surface elevation relative to the mean sea level. We present detailed synthetic aperture radar (SAR) interferometric analyses on persistent point targets for the historical center of Venice, the tourist area of Sottomarina, and the Zennare farmland close to the southern lagoon edge. The selected areas are characterized by different degrees of development and our analyses show the remarkable capability of SAR Interferometric Point Target Analysis (IPTA) to map land displacement rates in densely urbanized zones and to detect movement information on isolated structures with a mm/year accuracy. A detailed analysis of the time series from 1992 to 2000 provided by IPTA shows that the vertical component of the measured displacements are the superposition of a short timescale, generally seasonal, movement on the order of 1 cm that is likely related to the fluctuation of environmental variables (temperature, piezometric head in the aquifer system underlying the lagoon, sea/lagoon water level) and a long-term ground deformation associated with building construction, the geomorphology of the area, and the human development of natural resources. If Venice is confirmed to be generally stable, significant long-term subsidence on the order of 4 mm/year is detected at the Sottomarina coastland. The highest displacement rates, of up to 8-10 mm/year, are recorded in the farmland bounding the lagoon margin where the movements are found to be highly site-specific.