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NEW PRODUCTS AND INNOVATIONS Mapping ground movement from space May 2012
TunnelTalk reporting
Satellite technology is the new tool in the arsenal of facilities employed to detect millimetric surface deformation associated with tunnel and underground space excavation and construction.
Satellite monitoring

Satellite monitoring

Altamira Information, a specialist satellite earth observational company, has developed and makes available the InSAR SPN technique that is able to detect ground movements on the earth's surface with millimetric precision. This is achieved by using radar satellite images that detect and measure the movement of reflectors on the surface with every successive pass of the satellite over the same area.
Millimetric changes in the position of reflectors set at multiple locations on the orbital sweep of the satellite effectively identifies ground movement hot spots that are then displayed on colour-coded maps.
Fig 1. Principles of InSAR technology

Fig 1. Principles of InSAR technology

"The range of movement that can be measured using this technique depends on the satellite and the number of images used for the period of the study," explained Maria de Farago, Remote Sensing Geologist with Altamira Information. "This remote sensing technology is particularly effective in studying cities, as buildings and infrastructure serve as almost perfect reflectors to the radar signal."
An extensive archive of radar images already exists and includes data from 1992 onwards. These archives make it possible to perform historical studies of ground deformation over long periods of time and, due to the dimensions of the radar images, across very large areas.
Given that the smallest radar image is 40 x 40km wide, and with high radar signal reflectivity of an area, as is the case particularly in urban areas, InSAR technology can provide ground deformation data for wide areas with a precision of +/- 3mm per measurement and to a density of measurement points from 1,000 to 25,000 points/km2.
Studies of historical data from the archive will reveal areas already affected by movements before work begins on a new tunnelling project.
Historical data of an area before work starts on a high-speed railway project tunnel

Historical data of an area before work starts on a high-speed railway project tunnel

During the tunnelling project, the satellite monitoring technology can be programmed to provide updates of the deformation measurements of the reflection points on the ground.
Altamira Information has implemented the technology on various projects around the world to monitor metro line construction in several cities including Madrid, Barcelona (Fig 3), Bilbao, London (on the Jubilee Line Extension of the 1990s), Santiago de Chile and Warsaw, among others. InSAR SPN results show areas of subsidence coinciding in time and space with the construction period and location of tunnel and underground station excavations for these projects.
Fig 3. Surface movement monitoring above an underground car park and the metro line in Barcelona

Fig 3. Surface movement monitoring above an underground car park and the metro line in Barcelona

In some cases, the results have shown movements on buildings and structures starting during tunnel construction, as well as movement accelerating in areas affected by ground movements created by previous construction projects.
The application of satellite technology in the field of tunnelling and underground space excavation holds significant potential in the process of monitoring and reacting to surface settlement and ground movement. The launch of new radar satellites will improve time spatial and temporal resolution, which will result in improvements to the detection, measuring capabilities and evolution analysis of movements detected using radar satellites.
Altamira Information is to have an exhibition stand at the ITA World Tunnel Congress (WTC) in Bangkok in May 2012 and will also present a technical paper, entitled Urban tunnelling and the advantages of using InSAR SPN satellite technology to detect and monitor surface deformation. Both will provide further information about the technology and the services offered by the company.
References
WTC exhibitors preview and stand locator - TunnelTalk, April 2012
WTC2012 Bangkok Preview - TunnelTalk, April 2012
WTC2012

           

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