Today, this established method is a precise and cost-effective tool for quantifying ground movements without the need for advanced geotechnical measurement equipment of expensive field investigations.
InSAR uses the difference in radar signals between data acquisitions to detect movements over time. Displacement in both ground and built-up structures can be measured, allowing for applications such as soil settlement, ground subsidence, or infrastructure monitoring, related to mining or the onshore oil and gas industries. The technique can also be utilized for risk or environmental assessments in addition to local and regional geohazards studies. Unlike other remote sensing devices, SAR sensors are independent of weather and illumination. Use of InSAR allows for the identification of hotspots, which in turns allows for more informed design of further in-situ measurements.
InSAR at NGI
InSAR-related activities at NGI have focussed on ground settlements in built-up areas and on dams, regional subsidence analyses, and landslide detection. This last example particularly related to development projects.
Use of InSAR for subsidence and settlement monitoring
InSAR is often used to investigate and monitor mining areas, dams, and other man-made structures. NGI has used InSAR to investigate subsidence due to groundwater extraction in Vietnam, settlement of the Svartvatn dam in southern Norway, settlement issues at Bjørvika, Oslo and evaluation of possible surface settlements along the Follobane railway tunnel going south from Oslo.
Deformation analysis of the Svartevatn dam, based on the InSAR technique, shows a settlement rate of approximately 3 mm/year at the centre of the dam. Satellite scans were taken by the ERS satellite between 1992 and 2000. (Satellite data: Copyright © European Space Agency)
Example results from InSAR measurements with web-based presentation, from Oslo S area, on a Project for Bane Nor.
Use of InSAR in Landslides
InSAR techniques are useful tools for estimating the size of movement of a landslide, especially when the slide area is very large. GPS and other measurement techniques can measure this as well, but only at a limited number of discrete points and are very expensive in comparison. Radar images give a good overview of areas in motion, and can provide measurements over many years, provided that images are available. By using images from a sensor with a short wavelength and by using 25 or more scenes, one can obtain a long and precise time series of the region's movement in two dimensions.
Deformation analysis of a slow-moving landslide in Nainital, India monitored using InSAR. Satellite imagery from Envisat. (Satellite data: Copyright © European Space Agency)
Other Applications of InSAR
InSAR can be used to measure volcanic, seismic, and tectonic deformation, as well as classify ground cover, detect changes, and measure glacier movement..
Current R&D at NGI
- Settlement and subsidence in urban and rural areas, both within and outside of Norway
- Settlements of dams and large structures
- Detection of landslides and terrain deformations, and monitoring and measurement of movements
- Processing and analysis of TSX Staring Spotlight data
- Assess potential to use InSAR in industrial areas for monitoring tailings and tailing dams
InSAR Related Services
- Mapping and monitoring of settlement and subsidence
- Mapping and monitoring of terrain deformation (e.g., landslides) worldwide
- Very-high resolution and detailed analyses to supplement Norwegian national-scale overview mapping by NGU
Software and Equipment in use at NGI
- Gamma Remote Sensing AG (Gamma software, GPRI)
- sarmap SA (SARscape)
- ERS, ENVISAT, ALOS, Radarsat-2, TerraSAR-X