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Tandem satellites

October 20, 2010

Four months after the second of the two satellites was launched, a satellite tandem is in position and has begun its mission of taking high-resolution photographs of the Earth's surface.

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Image of Mt. Etna, as produced by the satellites
Italy's Mt. Etna was the first location to be imagedImage: DLR

The German Aerospace Center (DLR) announced Tuesday that its two satellites currently flying in tight formation around the Earth have acquired their first detailed image of the Earth's surface. The new image details Mt. Etna, on the eastern coast of Sicily, in Italy's southern island province.

The satellites, TanDEM-X and TerraSAR-X launched in June 2010 and June 2007, respectively, are currently flying just 350 meters (1,100 feet) apart on a mission to photograph the surface of the planet in unprecedented detail.

Artist's rendition of how the satellites survey the Earth's surface
The satellite measure the same points from two anglesImage: picture-alliance/dpa

Using a process called bistatic radar, the satellites send microwave pulses from their approximate 500-kilometer orbits to Earth and measure how long it takes for pulses to bounce back from the Earth. Then the satellites' on-board computers determine the height of the ground surveyed. German space authorities said the level of accuracy this method produces is unprecedented.

"Processing the bistatic pairs of data is a big challenge," Thomas Fritz, a DLR processing engineer, said in a statement. "Everything must match up exactly in order to reach this level of precision. All sorts of data can affect the algorithms, from synchronization signals to millimeter-accurate orbital calculations."

Prior to this new German project, the best digital elevation survey came from the US Shuttle Radar Topography Mission (SRTM) completed in 2000, however it only imaged 60 percent of the Earth's surface and was not nearly as accurate as the new survey.

Survey will take years to finish

Illustration of the satellites' orbits around the Earth
The satellites fly in a formation similar to a double-helixImage: DLR

DLR officials have said previously that the project will take four years to complete the survey and to process its corresponding data. They expect the final amount of data collected to reach around 15 terabytes, or approximately 60 computer hard drives.

The raw data will be processed by three ground stations in Sweden, Canada and Antarctica and then will be sent for final processing to the German Remote Exploration Data Center (DFD) in Oberpfaffenhofen, just outside of Munich, in southern Germany.

The new three-dimensional map will be made available to planetary scientists and to the private sector, with potential applications in mobile phone network construction, flight plan creation and urban planning.

Author: Cyrus Farivar

Editor: Sean Sinico

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