Measurements of deformation
InSAR as a method uses radar signals from satellites to measure changes in height in the surface. Advanced processing algorithms makes it possible to measure millimetre scale movements in the surface. The method works best on surfaces with little or sparse vegetation, because the radar signals are reflected by solid surfaces, such as rocks. Regions with optimal surface may provide full covering measurements.
No InSAR measurements can be obtained when the surface is covered by snow. To get measurements during winter also, NGU and NVE install reflectors in certain unstable rock slopes. The reflectors provide frequent measurements all year round at the locations they are installed.
In addition to InSAR, measurements of deformation in unstable rock slopes are done using a precise GPS method. GPS can be applied in all accessible places and provides the full three-dimensional vector of movement. The measurements are done either on permanent GPS installations that measure throughout the year or by episodic measurements of bolts mounted in rock. The episodic measurements are typically done every one or two years together with mapping fieldwork.
The combination of InSAR and GPS with structural mapping and other measurements in the field provides the geologists with detailed knowledge about where and how the deformation occurs.