Satellite measurements provide safer E18-construction

Accurate data from InSAR satellite measurements will be used to monitor the construction of the E18 motorway just west of Oslo. Movements and ground displacements will be registered with millimetre precision before, during and after the construction work. This marks the first time that the Norwegian Public Roads Administration (SVV) is using InSAR measurements to monitor displacements on a major road project in Norway.

– With this innovative method we will acquire detailed knowledge about movements of the ground due to construction of the E18. Displacements or ground movement may cause damage to nearby houses and infrastructure. If such movements are detected at an early stage it will reduce the risk of costly mitigation. This will provide greater safety for the public, and in the long term, we hope to save substantial amounts, says Grete Tvedt, project manager at SVV.

The traditional method of monitoring settlements is to measure the displacements of survey markers at some discrete points. InSAR data comes as an important supplement to this method and will provide a more comprehensive overview of the development of settlements.

NGI has recently signed a contract with the consulting company Aas-Jakobsen AS to provide InSAR data for SVV during the E18-development. The satellite-derived results will be used by Aas-Jakobsen AS, which along with Geovita AS, will interpret the information and evaluate possible damages due to settlements from the construction work.

Example results from InSAR measurements with web-based presentation, from Oslo S area, on a Project for Bane Nor.

– We have for quite some time cooperated with Airbus, which owns the commercial TerraSAR-X satellite. Since NGI has already been involved with other types of ground surveys along the planned E18-route, it was advantageous to buy InSAR-data for this area, says Regula Frauenfelder, project manager at NGI, and responsible for Remote Sensing and GIS at NGI.

– The remarkable feature of the data is the very high resolution. Each pixel in the satellite image represents 1 x 1 m. One building or house may, for example, have up to 10 measurement points, and in total there are tens of thousands of points where we can monitor eventual movements in the ground.

By comparing the InSAR data from before the road construction with measurements in the future, we can monitor how the construction activities affect the ground conditions and behaviour. If movements or displacements occur, the monitoring data will help determine if they are a result of man-made or natural causes.

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FACTS - What is InSAR?

Interferometric SAR (InSAR) is used to measure and quantify terrain movements, for example landslides or avalanches, subsidence or other ground displacements. In 1999, it was for the first time demonstrated how radar satellites could be used to detect movements in the ground, all the way down to the millimetre level accuracy. InSAR is a technique that uses differences in the radar signal between images taken at different times to identify changes.