1,721,058 research outputs found
Comment on "Recent subsidence of the Venice Lagoon from continuous GPS and interferometric synthetic aperture radar" by Y. Bock, S. Wdowinski, A. Ferretti, F. Novali, and A. Fumagalli
No full textRelative sea level rise, i.e., the combination of land subsidence and the eustatic rise of the sea level, is a major problem for the safety of Venice since the 1970s [e.g., Gambolati et al., 1974; Carbognin et al., 1977]. The most recent paper on the subject has been published by Bock et al. [2012]. In this Comment we (1) dispute the originality of the combined GPS and InSAR method presented by Bock et al. [2012] who missed some previous publication on the subject; (2) contest their statement of possible “bias” in our previous analyses which used similar methodologies; (3) question the “precision of 0.1–0.2 mm/yr with respect to a global reference frame” declared by the authors; and, (4) discuss on the meaning of “stability” versus “subsidence” for a coastal city like Venice settled above ~1500-m
thick Quaternary unit with 20–30 m of Holocene poorly consolidated lagoon deposits
TerraSAR-X reveals the impact of the mobile barrier works on Venice coastland stability
No full textLand subsidence and eustacy concurred to make the relative sea level in Venice (Italy) 23 cm higher over the last century. In order to protect the city and its lagoon environment from increased flooding, a series of mobile barriers are under construction at the three inlets of Lido, Malamocco, and Chioggia connecting the Adriatic Sea to the inner water body. Since 2003 work has been proceeding with the reinforcement and extension of the existing jetties and the construction of breakwaters, harbors, and a small island within the Lido inlet. We detected significant local settlements of a few centimeters between March 2008 and January 2009 at the three inlets induced by the construction works through an interferometric analysis of 30 satellite radar images acquired by the new German TerraSAR-X mission. On a more regional scale we observe that the city of Venice and the other major urban settlements on the lagoon littorals are not impacted by subsidence during this period. The very high spatial resolution of 3 m and the short repeat-time interval of 11 days of
TerraSAR-X enable the investigation of displacements with an unprecedented observed level of details, opening new perspectives to geodynamic's research and civil engineering sectors for the monitoring of large infrastructures with potential vulnerability to terrain motion
Integrating geotechnical and interferometric SAR measurements for secondary compressibility characterization of coastal soils
No full textPersistent Scatterer Interferometry (PSI) provides a new perspective to monitor the movements of coastal structures due to long-term consolidation using satellite-borne remote sensors. The method has the advantages of detecting the displacements at a very high spatial (from 1 to a few meters) and temporal (from 10 to 30 days) resolution. Cost-effective monitoring of complex and large (some kilometre long) structures can be done over long-time (up to 10 years) intervals, and at large-scales (tens times tens km2) of investigation. Here, these measurements are integrated with geotechnical, site-specific, measurements to characterize in a unique framework the long-term compressibility of coastal soils over large areas. The approach is tested on the 60-km long coastland of the Venice Lagoon, Italy. An accurate quantification of the movements of coastal infrastructures at the Venice coastland is carried out by PSI using ENVISAT ASAR and TerraSAR-X images acquired from April 2003 to December 2009 and from March 2008 to January 2009, respectively. Several nearshore and offshore structures were constructed over the decades to protect Venice and its coastal environment from sea storms and high tides. Long jetties were built at the lagoon inlets since the end of the 18th century, significantly reinforced between 1994 and 1997, and finally reshaped since 2003 in the framework of the MOSE construction (i.e., the project of mobile barriers for the temporarily closure of the lagoon to the sea). The measured displacements range from a few mm/yr for the structures older than 10 years to 50-70 mm/yr for those realized a few years ago. The PSI measurements are combined with the outcome of a detailed geomechanical characterization of the lagoon subsoil obtained by a field-scale experiment started at the end of 2002 and monitored to 2008. The use of the stress-strain properties derived from the trial embankment and the actual lithostratigraphy below the coastal structures, which is available from several piezocone profiles and boreholes, allows for the computation of secondary compression (consolidation) rates that match very well the PSI-derived movements. The results provide important information on the potential of using PSI to characterizing geotechnical properties (magnitude and distribution) of coastal deposits, as well as to estimate the expected time-dependent geomechanical response of coastal structures or other large constructions
Evidence of the present relative land stability of Venice, Italy, from land, sea, and space observations
No full textThe 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
Monitoring Land Subsidence in the Euganean Geothermal Basin with Differential SAR Interferometry
No full textLand subsidence monitoring with differential SAR interferometry
No full textThe potential of differential SAR interferometry for land subsidence monitoring is reported on. The principle of the technique and the approach to be used on a specific case are first presented. Then significant results using SAR data from the ERS satellites for various sites in Germany, Mexico, and Italy, representing fast (m/year) to slow (mm/year) deformation velocities, are discussed. The SAR interferometric displacement maps are validated with available leveling data. The accuracy of the subsidence maps produced, the huge SAR data archive starting in 1991, the expected continued availability of SAR data, and the maturity of the required processing techniques lead to the conclusion that differential SAR interferometry is suitable for operational monitoring of land subsidence
On the application of SAR interferometry to geomorphological studies: Estimation of landform attributes and mass movements
No full textThis paper presents two examples of application of Synthetic Aperture Radar (SAR) interferometry (InSAR) to typical geomorphological problems. The principles of InSAR are introduced, taking care to clarify the limits and the potential of this technique for geomorphological studies. The application of InSAR to the quantification of landform attributes such as the slope and to the estimation of landform variations is investigated. Two case studies are presented. A first case study focuses on the problem of measuring landform attributes by interferometric SAR data. The interferometric result is compared with the corresponding one obtained by a Digital Elevation Model (DEM). In the second case study, the use of InSAR for the estimation of landform variations caused by a landslide is detailed. © 2004 Elsevier B.V. All rights reserved
Quantitative evidence that compaction of Holocene sediments drives the present land subsidence of the Po Delta, Italy
No full textDeltas are highly dynamic coastal systems that over the last few decades have generally experienced a substantial area loss caused by trapping of river sediments in upland drainage basins as well as land subsidence due to natural and anthropogenic causes. A major example is the Po Delta in the Mediterranean in northeastern Italy. This area has experienced as much as 3 m of land subsidence from the 1930s to the 1970s primarily because of the extraction of gas‐bearing waters. However, present subsidence rates are largely unknown and the ground settlement is supposedly controlled by natural long‐term deep processes. We have combined radar Interferometric Point Target Analysis (IPTA) with previous geomorphological investigations on aerial/satellite images and seismic surveys, and geochronological data from core samples and geomechanical in situ tests, to assess the current sinking of the delta and to understand the processes controlling the vertical movement. The high density of the measurable point targets (more than 15,000) allows characterization of the spatial variation in the vertical land motions (VLM), ranging from −1 to −15 mm/yr. We find that subsidence rates are significantly correlated with the age of highly compressible Holocene deposits that compose the shallowest 30–40 m of the sedimentary sequence. A typical log‐type consolidation equation applicable at the scale of the entire delta has been obtained. We conclude that the consolidation of late Holocene sediments is the major cause of the present land subsidence in the Po River delta. This finding has significant impact on the understanding of many other modern deltas that were formed in the lower Holocene epoch
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