TanDEM-X and WorldDEM

What it is

TanDEM-X is a German radar satellite launched on 21 June 2010 from Baikonur to fly alongside its near twin TerraSAR-X, in orbit since 2007. Together they form the first bistatic radar interferometer in space. The mission is a public private partnership between DLR and Airbus, which built the satellites and markets the commercial product, WorldDEM.

How it works

Each satellite sends and receives radar pulses. Because the two fly in close formation, only a few hundred metres apart, they see every patch of ground from slightly different angles at the same instant. The tiny difference between the two echoes reveals height. Taking both views simultaneously avoids the errors that creep in when one satellite revisits a site days later, after trees have moved or the atmosphere has changed. Radar also sees through cloud and works at night.

Why it stands out

Between 2011 and 2015 the pair covered the entire land surface several times. DLR processed about 3 petabytes of data into roughly 19,000 tiles, and production of the global elevation model finished in September 2016. The grid spacing is 12 metres with relative vertical accuracy better than 2 metres; versions at 30 and 90 metres also exist. The satellites were designed for five years and are still working after more than fifteen. Operations run from the German Space Operations Center in Oberpfaffenhofen.

Where you meet it

Elevation data underpins flood modelling, aviation obstacle charts, pipeline and road planning, mobile network planning and military mapping. Scientists use repeat measurements to track ice sheets, forests and permafrost.

A lower resolution 90 metre version has been released for scientific use, which is why TanDEM-X heights now turn up in research on glaciers, rivers and coastlines far from Germany. The mission is controlled from Oberpfaffenhofen near Munich, with commands sent through the Weilheim ground station.

Sources

• DLR: TanDEM-X
• State Space Agency of Ukraine: TanDEM-X marks 15 years