High-Resolution Interferometric Observations/Measurements over the Rio-Antirio Cable-Stayed Bridge (Greece)
Parcharidis, Issaak¹; Benekos, George¹; Foumelis, Michael²; Stramondo, Salvatore^3
1Harokopio University of Athens, GREECE; ²ESA-ESRIN, ITALY; ³INGV, ITALY

During the last decade the detection, mapping and monitoring of ground deformation at centimeter to millimeter resolution with space-borne SAR interferometry reached some maturity and the technique has become a very useful remote sensing tool. The general trend of the aerospace industry towards increasing spatial resolution and repeat-cycle of space-borne SAR sensors enabled the monitoring of an individual construction over very fine scales.
By definition ground motion is the surface expression of different physical events like subsidence, earthquakes, landslides etc. In many cases the deformation is of anthropogenic cause relate to water and oil pumping, slopes undercut by roads, mining etc. Construction and operation of engineering structures and generally of big projects in urban or in rural areas can be seriously affected by ground conditions leading to casualties and financial losses. Prevention and management of these risks are of great importance. In reality, usually structures are not affected by maximum ground displacement, but by the differential displacement that they suffer. Uniform displacement of a region may not be even noticeable. Similarly, uniform displacement of a structure does not damage the structure. It is the differential displacement that affects the structure: For rigid structures, if their tilt is considerable, it can result in overturning or in buildings can make the building uninhabitable. For concrete structure founded in separate footings, when differential settlement among footings is large, large forces will be applied at the concrete skeleton of the structure and the structure may collapse.
The Rio-Antirio bridge, located in western Greece, is the longest multi-span cable-stayed bridge of the world with 2,252 m of suspended deck and two viaducts of 392 m on Rio and another of 239 m on Antirio side. The broader area presents a combination of geohazards such as deep soil strata of weak alluviums, strong seismic activity, tectonic movements etc, which make the area of great ground deformation susceptibility and the bridge an element at risk.
The present work, carried out in the frame of ESA's Terrafirma GMES project, concerns PSI analysis over Rio-Antirio cable-stayed bridge in order to estimate potential deformation occurring along the structure using X-band interferometric SAR observations. A dataset of 34 TerraSAR-X Stripmap scenes covering the period of 2010-2012 were utilized. The interferometric processing was performed using GAMMA's Interferometric Point Target Analysis (IPTA) software packages. For the Rio-Antirio bridge due to its characteristics (suspended deck), coherent targets could only be detected on the four pylons as well as along both viaducts. The obtained interferometric results consist of the estimation of scattering heights, linear deformation rates, atmospheric phase screen, temporal coherence and non-linear deformation histories for each geocoded point target. Independent PSI processing's considering different local reference points at both sides of the bridge were performed to investigate possible dependency on the results. This is crucial since different behavior in terms of long-term geologic-tectonic motion is reported for the region.
TerraSAR -X PSI measurements provide information on the relative deformation pattern of the structure itself. The high resolution SAR observations provide valuable information about the stability through a number of targets detected from viaducts and pylons structures.