Frequently asked questions
What is InSAR?
Interferometric Synthetic Aperture-Radar (InSAR), also known as radar interferometry, is a technique that allows us to detect and tract ground motion. Using the most recent radar data and advanced algorithms, we can determine the millimeter-scale movements in, for example, urban areas with subsidence or unstabel rock slopes in the terrain.
How does InSAR work?
A radar satellite emits pulses of radar energy, which move like waves towards Earth's surface. When such a pulse of radar energy is scatters across the Earth’s surface, a signal reflects back to the radar satellite.
When such a pulse of radar energy is reflected back to the satellite, two types of information about the wave are recorded: amplitude and phase. The amplitude strength is influenced by factors such as the surface material, the slope of the surface and surface moisture content, and to a lesser extent, atmospheric conditions.
By combining (or interfering) measurements from the same area at two different times one can determine, with a very high level of accuracy, whether or not movement has occurred during that time. We can create a time series of ground surface movements by combining numerous measurements.
How is InSAR used in Norway?
NGU uses InSAR to help detect and monitor landslides and urban subsidence. This method is particularly useful in areas that are difficult to reach, like unstable rock slopes. Assuming optimal conditions, we can attain detailed images of fractures in a rock mass, without setting foot outside the office. InSAR can work very well in urban settings when there are buildings and road surfaces to reflect signals.
Can you acquire InSAR images anywhere?
To acquire data, we must identify a stable, reflective object on the surface that can serve to reflect radar signals. An example of such a surface is a roof or exposed rock. Ground covered with a lot of vegetation does not give good reflections. InSAR works best in urban areas and bare terrain. Snow can affect the signal due to its water content. Thus, we only use data from periods with relatively little snow cover (June-October).
How often can you acquire data?
The Sentivel-1 satellites acquire images over Norway every six days.
Who owns InSAR data?
The sentinel-1 satellites are part of the European Union’s Copernicus space program that operates with an open data policy. The raw data is freely available to anyone, but special software is required to get the ground movement.
What does NGU do with InSAR data?
NGU has used InSAR to map and monitor movement in unstable rock slopes and steep terrain for many years. In 2016, NGU received support from the Norwegian space agency and NVE to establish a national center for ground movement. The center’s aim is to make deformation maps easily available to everyone. InSAR processing at NGU is done using software developed by the research institute Norut, in Tromsø.
How can I use InSAR data?
Simply go into the map service and zoom to an area of interest and view the processed InSAR data. You can display the time series of a point, by clicking on it.