Earth Observer Sentinel-1: Satellites with radar vision

You don't need a satellite image to see that things are changing here, but the radar images of the Copernicus mission Sentinel-1 provide more clarity. Often degradation of the Earth's surface is due to changes that take place largely underground — for example, due to groundwater extraction, the natural compaction of sediments, urbanization or, as in this case, mining.

This map shows how the land surface in the Rhineland mining basin in Germany has shifted several millimeters each year between 2014 and 2019. The degradation shown in red is clearly attributable to open-cast lignite mining and the simultaneous reduction of the groundwater table. The blue spots in the adjacent area are probably related to the rise in groundwater after mining ceased.

The fact that Sentinel-1 has mapped tiny shifts in the land surface throughout Germany is new. However, the mission has been serving science for quite some time: Sentinel-1A was launched in 2014, and Sentinel-1B followed in 2016. Since then they've been collecting data that is accessible to everyone and is used for environmental, climate impact research, transport, economic and security purposes.

This image was taken using data from 2014 to 2016. It shows surface degradation caused by salt mining around Veendam near Groningen in the northeast of the Netherlands. Green dots indicate where the land is stable. Orange and red represent sinkages in the Earth's surface.

Such ground changes don't just occur in the salt mining areas of the Netherlands, but also in black coal mining areas like here in Witten, near the Ruhr River in Germany. Landslides, shaking and sinkholes can occur when underground mines collapse. This can cause dangerous damage to buildings, both in urban and rural areas.

Images taken from space can be useful for authorities to improve urban planning or even to detect problematic erosion before it's visible to the naked eye. Here you can see the depressions along the Markermeer, a lake in central Netherlands. Eroded areas are shown in red, while the green areas show where the ground is stable.

Osmundneset, located on the east side of the Norwegian Hyenfjord, is a large unstable rocky slope. The dark red dots indicate erosion of as much as two centimeters per year between 2015 and 2018. The green dots show areas that have experienced minimal change. Researchers want to understand the geological conditions and risks in order to set up a 24/7 early warning system, if necessary.

The Sentinel-1 satellites have shown that the Millennium Tower in downtown San Francisco sinks a few centimeters each year. The study of the city helps scientists to improve the monitoring of urban ground movements, also with regard to erosion and degradation hot spots in Europe.

Other parts of San Francisco have also been mapped, such as the buildings along the earthquake prone Hayward Fault Zone, which runs along the right. On the left, the degradation (yellow/orange) of the newly reclaimed land in San Rafael Bay can be seen. On the lower right a slope is visible, which likely occurred due to the recovery of the water table after four years of drought.

Data from the Sentinel-1 satellites collected between December 26, 2014 and October 28, 2016, show that parts of Oslo's railroad station are sinking by 10-15 millimeters per year. This corresponds to a vertical drop of 12-18 millimeters per year. The fact that the Opera House — the white building on the fjord south of the depression area — has not moved is also clearly visible.

It's not only the Sentinel-1 pair that belongs to the Earth observation program — satellites up to "6" are now in orbit. The newest member of the family was launched on November 21. Researchers want to use "Sentinel 6 Michael Freilich" to take a closer look at the oceans from space, for example to measure and map the rise in sea level.