TanDEM-X and TerraSAR-X – imaging Etna while flying in formation

The image shows Mount Etna on the east coast of Sicily. On the left of the image, in the foothills of the volcano, the city of Catania is visible as a collection of white points. This three-dimensional view of the volcano was generated from data recorded by TanDEM-X and TerraSAR-X. This was acquired using bistatic radar, where one of the satellites transmits a radar signal to Earth and the two satellites receive the reflection of this signal simultaneously. In this way, a highly accurate three-dimensional terrain model is created on a 12-metre grid. A similar recording technique was used in the Shuttle Radar Topography Mission (SRTM) in February 2000. However, in this case only 60 percent of Earth's surface was imaged, and at a coarser grid spacing of 30 to 90 metres

This is partly down to the greater accuracy of the elevations measured by TanDEM-X and TerraSAR-X; as they flew over at an altitude of over 500 kilometres, the two radar satellites were able to detect detail on Etna that SRTM could not resolve. The other reason is that the volcano and its environs have changed over the course of the years; for example, to the south (left in the image) a lava flow from 2001 can be seen. The modern images use a finer measurement grid and enable geodynamic processes to be monitored. To create the three-dimensional elevation model of the entire land surface of Earth, the two satellites will fly over and image every area multiple times

Changes to Icelandic volcano Eyjafjalla are also visible in the two satellites' new elevation model. As they flew overhead, TanDEM-X and TerraSAR-X got sight of the volcano – whose ash cloud caused flight bans across Europe in spring 2010 – and took precise measurements of the rugged landscape of rock and ice. The colours indicate the height of the terrain; the peaks of the volcanoes are shown in white, while the lowlands where the melt water flows in spring are shown in green. The volcano’s crater, which was exposed from beneath the ice by its activity, is easily recognisable. To the right, another volcano, Katla, is ‘slumbering’ beneath a massive ice cap. The indentations visible in the ice indicate that this volcano is also active and that its ice cap is melting and collapsing as a result. Areas such as Iceland are being mapped in elevation for the first time by the radar satellites flying in formation, as the elevation model created by SRTM only reached 60 degrees latitude.

The adjustable flight formation and bistatic technique used by the two radar satellites make it possible for the data acquired to be analysed for a wide range of research on Earth. For example, bodies of water can be imaged without a problem for the first time. This involves the satellites synchronously generating an image of the area. In an initial successful test, DLR researchers observed the islands of Franz Josef Land in the Arctic Ocean. As if frozen in time, even the wave pattern of the sea can be recognised in the elevation model of the island group. Oceanography or climate researchers can also use such images to precisely analyse ocean currents, for example. In this image the highest areas are coloured white – the colour scheme thus roughly corresponds to the formation of ice on the islands.