Continuous Risk Assessment of Structures and Plants in Areas of Ground Deformation Susceptibility by Space-based SAR/ASAR Interferometry

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1 CCN4 Project Continuous Risk Assessment of Structures and Plants in Areas of Ground Deformation Susceptibility by Space-based SAR/ASAR Interferometry Issaak Parcharidis*, Michael Foumelis and Penelope Kourkouli Harokopio University of Athens Dep. of Geography ESRIN, Terrafirma phase 5th User Workshop 25-26/03/2009

2 Harokopio University of Athens/Faculty of Geography Scientific Coordinator: Dr. Issaak Parcharidis Subcontractors: University of Athens/Dep. of Geophysics and Geothermics Metrica S.A. GAMMA Remote Sensing (Switzerland) ESRIN, Terrafirma phase 5th User Workshop 25-26/03/2009

3 As pilot application the new bridge Rio-Antirio (Western Greece), an important infrastructure and its environment, was selected for monitoring and assessment. ESRIN, Terrafirma phase 5th User Workshop 25-26/03/2009

4 The main objectives of the project are : (i) mapping of past deformation (spanning over more than 15 years of archive data) (ii) Continuous monitoring, according to the revisit period of the satellite, attempting to create a regular updating of displacement maps (iii) producing deformation history charts for predefined prioritized point targets on the bridge as well as for the surrounding area showing not only the rate of deformation but also its temporal variation (iv) assessment of an operational use of the proposed technique and methodology and (v) estimation of the operating cost and comparison with ground techniques. ESRIN, Terrafirma phase 5th User Workshop 25-26/03/2009

5 The Rio-Antirio bridge is located at the intersection of two major roads: the Patras - Athens - Thessaloniki motorway which links the three most important cities of Greece and forms part of the European motorway network The bridge facilitates communication between Greece and Italy (and thus Western Europe) through the harbors of Patras and Igoumenitsa. The effects of the bridge change the revenue and work conditions of the adjacent areas and the conditions of social exclusion The Bridge plays a large role in the development, as an axis linking Greece to Europe, the Mediterranean and the Middle East ESRIN, Terrafirma phase 5th User Workshop 25-26/03/2009

6 The Rio Antirio Bridge is the longest multi-span cable stayed bridge of the World with its 2,252 meters deck Its foundations lay on a seabed that reaches 65 meters of depth. This is a world record for a bridge as well as their diameter of 90 meters making of them the world s largest bridge foundations. The Bridge has been awarded 9 International Awards by the international scientific community ESRIN, Terrafirma phase 5th User Workshop 25-26/03/2009

7 The Rio-Antirio bridge is built to withstand a collision of : tons tanker, wind speed of 250 km per hour and over 7 Richter scale earthquake Absorbing up to 2 meters displacement between any of its piers, the bridge is one of the safest places to be, should a major earthquake happen in the Patras area. ESRIN, Terrafirma phase 5th User Workshop 25-26/03/2009

8 The area of the Rio-Antirio strait presents a combination of hazards like : absence of stiff seabed strong seismic activity tectonic movements which make the area of great ground deformation susceptibility and the bridge an element in risk. ESRIN, Terrafirma phase 5th User Workshop 25-26/03/2009

9 ESRIN, Terrafirma phase 5th User Workshop 25-26/03/2009 The seabed profile presents steep slopes on each side and a long horizontal plateau about 60 meters below sea level. No bedrock has been encountered during investigations down to a depth of 100 meters below seabed. Based on a geological study, it is believed that the thickness of sediments made of thick layers of clay mixed in some areas with fine sand and silt is greater than 500 meters.

10 Seismicity during 2008 ESRIN, Terrafirma phase 5 th User Workshop 25-26/03/2009

11 Geological map of the area ESRIN, Terrafirma phase 5 th User Workshop 25-26/03/2009

12 Ground motion is the surface expression of different physical events like subsidence, earthquakes, landslides etc. In many cases the deformation is of anthropogenic cause related 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 ESRIN, Terrafirma phase 5 th User Workshop 25-26/03/2009

13 The proposal aims at testing a regular and continuous deformation monitoring over the structure itself and the surrounding area using advanced interferometric techniques and thus assessing the stability of the structure. ESRIN, Terrafirma phase 5 th User Workshop 25-26/03/2009

14 Monitoring and related processing are distinguished in two phases : (i) from 1992 to 2000 (pre-construction period) and (ii) From 2003 until the end of 2009 (end of bridge construction and regular operation). The last phase includes a first processing and then updating of processing every three acquisitions of repeated passes over the area. ESRIN, Terrafirma phase 5 th User Workshop 25-26/03/2009

15 The advanced interferometric method of examining interferometric phases from stable point-like reflectors is the most suitable for this application and specifically the IPTA algorithm of GAMMA Remote Sensing. First phase: 42 ERS SAR.SLC scenes Second phase: 28 ENVISAT ASAR.SLC scenes ESRIN, Terrafirma phase 5 th User Workshop 25-26/03/2009

16 A PSI analysis: The case of the Rio-Antirio bridge (1 st phase) A major processing difficulty of the specific case study was the inability to unwrap the entire scene using a single reference point. The presence of water body between the Rio and Antirio areas (distance >2 km) meant no targets were available in order to propagate the unwrapping procedure from one side of the land to the other. Therefore, a decision was taken so that two separate IPTA processing were performed using different reference points in the vicinity of Rio and Antirio areas respectively. ESRIN, Terrafirma phase 5 th User Workshop 25-26/03/2009

17 PS interferometric result of the Rio area

18 Typical displacement histories ( ) for specific point targets in Rio area. Displacement history of point 43329: A line of sight displacement of about 3cm (away from the sensor) is observed. Displacement history of point 45613: A line of sight displacement of about 1.5 cm (away from the sensor) is observed. An undulation pattern is apparent specifically during the period ESRIN, Terrafirma phase 3 User Workshop 25-26/03/2009

19 PS Interferometric result for the Antirio area

20 Typical displacement histories ( ) for specific point targets in Antirio area. Displacement history of point 36558: No displacement is observed. All values lie along zero value, meaning that this point remains stable during the whole considered period. Displacement history of point 36904: A line of sight displacement of about 1.5 cm (away from the sensor) is observed.

21 Point targets plotted over a Quickbird image in Google Earth environment with the related rate of deformation for each one in the Rio area and in a distance almost 200 m from seafront.

22 Point targets plotted over the geological map of Rio

23

24 Local GPS network covering spatially both sides

25 10 cm along the LOS 8/6/08 ML=6.5R Kato Achaia Interferometric pair / Bp=137 m Antirio 1.5 cm Rio 4 cm LOS Patra 5 cm epicentre

26 Start of 2 nd phase ENVISAT ASAR Average intensity image Task: deformation history charts for predefined prioritized point targets on the bridge

27 ASAR Interferometric Stacking Antirio Results consistent with ERS interferometric results Rio - 2 mm + 2 mm -4.2 mm - -3 mm/y +

28 IPTA Processing Candidate Points

29 2 nd Unrwapping st Unwrapping

30 The four pylons theoretically constitute excellent scatterers The deck is fully suspended and so it is difficult to detect scatterers on this. Potential scatterers of good quality on the bridge are found in an altitude range between 50 m and 120 m the bridge area in our DEM is defined as a zero altitude area redefine the sea-pixels as 1 cm of altitude A new processing is going on by creating a mask over the area where the bridge is located and giving an altitude value for the specific pixels of 50 m. On the two approach viaducts (for Rio and Antirio), a high number of scatterers of good quality are found.

31 Issaak please the final report! Issaak : Manager of the Bridge Project I need as much as more targets on the bridge!!!! (Mr. Papanikolas : Managing Director of the Bridge)

32 Thank you!