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Radar Interferometry and offset tracking
SAR satellites orbit around the Earth and take radar images at different times. When comparing images from different acquisitions, it becomes possible to detect distance change between the sensor and the ground surface, along the radar line-of-sight (LOS). The so-called Synthetic Aperture Radar Interferometry (InSAR) technique allows for measurement of ground surface displacements at millimetric-centimetric accuracy and is especially valuable to detect, map and monitor deep-seated landslides and superficial creeping landforms (Figure 1).
NORCE InSAR processing chain constitutes the backbone of the operational InSAR Norway ground motion mapping service (http://insar.ngu.no/), especially used by geologists to identify moving objects and evaluate the hazard they represent. In addition, we have several research projects exploiting InSAR for studying the kinematics of unstable mountain slopes and permafrost landforms in mainland Norway and Svalbard.
The loss of interferometric signal stability can limit the use of InSAR in areas characterized by very rapid movement. In these cases, another technique, called SAR offset tracking can be applied. The method is especially valuable for documenting objects with a velocity of several meters per year (e.g. glacial flow, destabilized rock glaciers).
Radar sensors can also be mounted on airborne or ground-based platforms to reach better spatial/temporal resolutions and have complementary acquisition geometries. NORCE owns a terrestrial radar, the Gamma Portable Radar Interferometer (GPRI). A GPRI allows for continuous monitoring at a second/minute resolution valuable for studying diurnal velocity variations in respect to external drivers, such as temperature and precipitation. The same system can be used on snow-covered surfaces and has the potential to detect millimeter snow deformation hours to days before snow avalanche release.
Figure 1. Synthetic Aperture Radar Interferometry (InSAR) for measuring ground surface displacements of gradually sliding/deforming rock slopes (landslides and creeping permafrost landforms).
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