German TanDEM-X satellite seeks 3D view of Earth
June 21, 2010
The TanDEM-X satellite has blasted into orbit on a mission to acquire the most precise 3D map of the Earth’s surface.
The German radar spacecraft will fly in formation with an identical platform called TerraSAR-X launched in 2007.
Together, the pair will measure the variation in height across the globe to an accuracy of better than two metres.
Their digital elevation model will have myriad uses, from helping military jets fly ultra 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 does 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 Dnepr rocket left its silo at 0214 GMT. A signal confirming TanDEM-X had separated successfully from the vehicle was picked up 29 minutes later at an Antarctic tracking station.
A digital elevation model has a host of applications
The new satellite was put into a polar orbit that is ever so slightly inclined to the one occupied by TerraSAR-X, some 514km above the planet.
The path of TanDEM-X across the sky means it will fly an extremely tight helix around its more established sibling.
The Dnepr emerges from its Baikonur silo to climb to orbit
“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 pair’s radars work by constantly bouncing microwave pulses off the surface of the planet. By timing how long the signal takes to make the return trip, the instruments can determine differences in height.
The compact orbital dance will give the pair “stereo vision”, by enabling them to operate an interferometric mode in which one spacecraft acts as a transmitter/receiver and the other as a second receiver.
Perhaps the best-known, publicly available, near-global, space-borne data-set prior to the German venture came from the US Shuttle Radar Topography Mission (SRTM) of 2000. A decade on, TanDEM-X should provide a big leap forward in capability.
“SRTM has a resolution of 30m, but the publicly available resolution is 90m,” Dr 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 metres. You have to stress the homogeneity - airborne lidar can achieve much higher resolutions but these models are only regional.”
To achieve the TanDEM-X level of detail on all 150 million sq km of the Earth’s land surface will require three years of operation.
Radar observations already have extensive military, civil, and scientific applications.
Good examples recently include the Eyjafjallajoekull eruption in Iceland and the Gulf of Mexico oil spill.
In the former, TerraSAR-X’s microwave vision was able to look through the ash plume to enable scientists to assess the developing status of the glacier volcano; and in the latter, the satellite has been able to follow the progression of the oil slick day or night from the way radar signals are reflected off the polluted water. This is possible because spreading oil has a tendency to flatten the sea surface and this effect is detectable from space.
TerraSAR-X looks through the Eyjafjallajoekull Volcano’s ash plume to see three craters. Such views are only possible with radar satellites
The improved dataset coming from the TanDEM mission should deepen and extend the range of radar applications.
Mobile phone operators will use the elevation model to work out the best places to position their masts; the aviation sector can use the information to plan safer flight paths; city planners need the data to assess flood risks in urban areas; maritime officials can even use the information to track pirates and vessels that fishing illegally.
The presence of oil in the water works to flatten the surface
The TerrSAR-X/TanDEM-X venture is operated on the basis of a public-private partnership. The German space agency owns the hardware; EADS Astrium builds it; and Infoterra GbmH has exclusive rights to commercialise the data.
Continuity is key to developing the radar applications market and already plans are in place to fly follow-on spacecraft.
The next step in development being pursued by the partnership is a high resolution, wide-swathe technology which would 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 metre,” Brig Gen Reiter said.
“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.
With a lot of processing, TerraSAR data can deliver a very detailed view
Source: bbc.co.uk/
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