When the ground in the Rhenish lignite mining district sags

Dhe open-cast lignite mines in the Rheinische Revier between Cologne and Aachen are among the largest in the world. Although they are not the deepest open mining areas, they are one of the largest areas. The Hambach opencast mine extends over an area of ​​more than 43 square kilometers. This includes areas in which the lignite is mined, but also large areas in which the overburden, i.e. the removed soil, as well as the geological layers overlying the coal seams are accumulated for later recultivation.

In some of the open-cast mines, the ground subsidence is considerable. In addition, the slopes along the pits become unstable over time and can slide, which is dangerous for people and buildings. In order to identify the risks early and to be able to take measures in good time, the mining areas must be continuously monitored. A German-Chinese research group has now developed a new method with which both the vertical ground movements in an open-cast mine and the stability of the flanks of the pits can be recorded from space with earth observation satellites.

Germany is a stable country - at least from a geological point of view.  Researchers at the ground movement service of the Federal Institute for Geosciences and Natural Resources (BGR) in Hanover have now created a map of the uplift and subsidence of the soil in Germany over the past four years based on measurements from the European pair of radar satellites Sentinel-1.  The very largest area appears in green on this map, which means that no vertical ground movement could be measured.  But the map also shows some very small bruises in which the ground has lifted up to five millimeters a year.  Soil subsidence (in red and yellow) occurs mainly in North Rhine-Westphalia.  They are a direct consequence of mining, for example in the Ruhr area, where until recently hard coal was mined underground.  There subsidence rates of five millimeters per year were measured.  The largest red area on the map is in the far west of the country in the Rhenish lignite area between Cologne and Aachen.


Germany is a stable country – at least from a geological point of view. Researchers at the ground movement service of the Federal Institute for Geosciences and Natural Resources (BGR) in Hanover have now created a map of the uplift and subsidence of the soil in Germany over the past four years on the basis of measurements from the European pair of radar satellites Sentinel-1. The very largest area appears in green on this map, which means that no vertical ground movement could be measured. But the map also shows some very small bruises in which the ground has lifted up to five millimeters a year. Soil subsidence (in red and yellow) occurs mainly in North Rhine-Westphalia. They are a direct consequence of mining, for example in the Ruhr area, where until recently hard coal was mined underground. There subsidence rates of five millimeters per year were measured. The largest red area on the map is in the far west of the country in the Rhenish lignite area between Cologne and Aachen.

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Image: BGR

Radar satellites keep an eye on ground movements

In order to be able to measure the ground movements associated with mining in the Rhenish Revier, the researchers led by Mahdi Motagh from the Geo Research Center in Potsdam used the data from, among other things, the German radar satellite „Terrasar-X“ and the satellite duo „Sentinel 1A und 1B“ of the European Copernicus program. The three scouts circle the earth at altitudes between 500 and 700 kilometers. They continuously send out radar beams and register the portion that is reflected from the earth’s surface.

For many years now, scientists have been using such radar measurements to measure ground movements that occur in active volcanoes or as a result of earthquakes or are caused by pumping out large amounts of groundwater. The radar signals that the satellites have measured in two successive orbits from exactly the same area of ​​the earth’s surface are superimposed.

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