June 21, 2010

Germany Launches 3D Imaging Satellite

The German TanDEM-X satellite has launched into orbit on a mission to acquire the most precise 3D map of the Earth's surface.

The radar spacecraft will fly into formation with an identical platform called TerraSAR-X launched in 2007.

The pair will both measure the variation in height across the globe to an accuracy of better than six feet.

Their digital elevation model will have a myriad of uses, such as helping military jets fly low to showing relief workers where an earthquake's damage is worst.

"Our aim is to generate a model at a resolution and a quality that doesn't exist today," explained Dr Vark Helfritz, from satellite image processing company Infoterra GmbH.

"This will be a truly seamless global product - not a patchwork of datasets that have been fitted together," he told BBC News.

TanDEM-X was carried into space atop a converted intercontinental ballistic missile from the Baikonur Cosmodrome in Kazakhstan.

The new satellite was put into a polar orbit about 319 miles above the planet.

TanDEM-X's path will fly a tight helix around its more established sibling.

"It is the first time that two satellites have been put in such close formation," said Brigadier General Thomas Reiter, the former astronaut and now executive board member at the German Aerospace Centre (DLR).

"Their orbits bring them together with a minimum distance of about 200m. This will be very challenging for mission controllers, as you can imagine."

The two satellites work by constantly bouncing microwave pulses off the surface of the planet.  The instruments can determine differences in height by timing how long the signal takes to make the return trip.

The compact orbital dance will give the pair "stereo vision," by enabling them to operate in interferometric mode in which one spacecraft acts as a transmitter/receiver and the other as a second receiver.

The U.S. Shuttle Radar Topography mission (SRTM) provided the best-known publicly available data-set prior to the German venture.

"SRTM has a resolution of 30m, but the publicly available resolution is 90m," Helfritz.

"With TerraSAR, we were able to produce a digital elevation model (DEM) around the 10m mark; and with TanDEM we are going down to two meters. You have to stress the homogeneity - airborne lidar can achieve much higher resolutions but these models are only regional."

The TanDEM-X level of detail of the Earth's entire land surface will require three years to complete.

Radar observations already have extensive military, civil, and scientific applications.

The improved dataset coming from the TanDEM mission should help deepen the range of radar applications.

The pair of satellites are operated on the basis of public-private partnership.  The German space agency owns the hardware and Infoterra GbmH has exclusive rights to commercialize the data.

The next step in development being pursued by the partnership is a high resolution, wide-swathe technology that could allow extremely detailed, large-scale images of the surface to be acquired in a single pass.

"We could decide to take a 100km swathe with a resolution of one meter," Brig Gen Reiter told BBC.

"That means two things, however. First, we can take a swathe and get all the products we need straight away; but second, the disadvantage is that we get incredible amounts of data and the challenge will be to get this data downlinked. The current downlink stations are reaching their limits."

This coming bottleneck issue is one of the reasons why Germany has chosen to lead the European Data Relay System (EDRS), a European Space Agency project that would see Earth observation data bounced off geostationary satellites using laser technology.


Image Caption: Flying in formation, TanDEM-X and TerraSAR-X will generate a precise global elevation model. Credit: DLR


On the Net: