Vertical movements caused by applied loads from buildings and infrastructure built on soft and compressible clays occur continuously, but with varying rate. Landslides in soft clay normally occur suddenly and there is no reliable system in place to indicate an increase in risk. It is hard to detect any movements prior to the actual landslide. These movements of the ground, whether they are attributed to natural processes or to human activity, are often sufficient to cause damage to buildings and infrastructure.
In 2008, Metria and the Swedish Geotechnical Institute (SGI) carried out a project to compare the vertical land movement measurements obtained using satellite radar images to those using traditional methods (RyS Dnr 171/07). The focus was subsidence of buildings and other man-made structures. A main conclusion of the project is that the resolution of the radar images (12.5m pixels from the ERS-1/2 satellites, which were further degraded pixels during the analysis) hindered the specification of objects that were measured. The main idea of this project is to build upon those results by utilizing very high resolution, TerraSAR-X images, which are available in resolutions of one to five meters, as the input into the differential interferometry analysis.
As demonstrated in the previous study, DInSAR/PInSAR can be used to detect vertical movements, although the accuracy needs to be enhanced. Using satellite images covers a wider area than the traditional methods, e.g. precision levelling and GPS, and provides additional information of the magnitude and distribution of the movements in an area. Even in areas where very precise movement measurements, as precision levelling, are needed the satellite images provide information on in which areas the precision levelling is most needed. It is also possible to ascertain eventual ongoing settlements in an area before e.g. an excavation.
The objective of the project is to investigate whether interferometry using very high resolution satellite radar images, can improve the previous results and provide detailed enough subsidence measurements in an urban area, to serve as the basis for a commercial service.
The approach will be to use the DInSAR method for detecting land movement over the urban area of Gothenburg in Sweden. To enable a comparison of results from TerraSAR-X and the ERS 1/2 satellites used in the previous project, the same area as in the previous project will be used. Results from this analysis will be compared with the reference data from subsidence measurements. In addition, height change measurements will be processed geo-statistically. The results and experiences obtained from the project will be discussed with the authority function of the SGI and demonstrated for the municipality with discussions focusing on ways of implementation. The project is a co-operation between the SGI and Metria together with the municipality of Gothenburg.
Swedish Geotechnical Institute (SGI):
Hjördis Löfroth, +46 13 20 18 54, firstname.lastname@example.org
Michael Ledwith, +46 8 57 99 72 98, email@example.com