InSAR uses the difference in radar signals between data acquisitions to detect movements over time. Displacement in both ground surfaces and built structures can be measured, allowing for applications such as building settlement, ground subsidence, or infrastructure monitoring, 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 turn allows for more informed design of further in-situ measurements.

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 is particularly related to development projects.

InSAR-related services

  • Settlement and subsidence in urban and rural areas
  • Settlements of dams and other large structures
  • Settlement monitoring of offshore structures
  • Consulting and detailed analyses to interpret and supplement national and international ground motion services

InSAR-related R&D

  • Monitoring of industrial areas, including mine tailings facilities and CO2 injection sites
  • Detection of landslides and terrain deformations, and monitoring and measurement of movements

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.

InSAR Mean Velocity 590

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)

INSAR Oslo S 583 381

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

  

Other applications of InSAR

InSAR can also be used to measure volcanic, seismic, and tectonic deformation, as well as classify ground cover, detect changes, and measure glacier movement. InSAR techniques are also useful for estimating the size of movement of a landslide, especially when the slide area is very large.

GNSS and ground measurement techniques are limited to a number of discrete points and are expensive to install and maintain. Satellite radar images provide a good overview of areas in motion, and can provide measurements over many years, provided that images are available.

By using images from a satellite sensor with a suitable wavelength and by using a stack of scenes, one can obtain a long and precise time series of the region's movement in two dimensions.

InSAR Skred 590

Deformation analysis of a slow-moving landslide in Nainital, India monitored using InSAR. Satellite imagery  from Envisat. (Satellite data: Copyright © European Space Agency)