TanDEM-X Mission Running Like Clockwork
Sophisticated Mission Planning Proven
Early 2012, the TanDEM-X mission completed an important milestone with the first complete coverage of the Earth’s landmass. This is an impressive achievement in this highly complex mission considering that the 150m sq.km. oflandmass had to be seamlessly covered.
This achievement proves that the highly sophisticated acquisition plan devised by the experts at DLR and Astrium over countless hours of computing, simulations and discussions is working. And not only that: the programming specialists were also able to fully secure the continued smooth acquisition and delivery of TerraSAR-X data to customers and scientists around the world. This meant assuring the uninterrupted acquisition of time-series data, integrating short-term requests in case of unexpected events as well as executing large-scale regional monitoring and mapping projects on schedule together with all other routine data orders. The programming experts at DLR have truly mastered a mammoth task juggling all these different requirements.
Precision and Quality
From a technical point of view, the mission is already a huge a success. TerraSAR-X and TanDEM-X reliably record imagery in bi-static mode, which means that both instruments work simultaneously in a fully synchronised way. This requires precise coordination of data from and between both satellites, as a millimetre of variation can mean an elevation error of up to one metre. For example, differences in the cable lengths on the two radar instruments, as well as the distance between the two satellites, need to be calibrated very precisely.
“The precision of the DEMs already achieved by the first coverage impresses even us. In some areas with “easy” terrain characteristics, like for example the vast majority of Australia's landmass, just this one overflight has already delivered the quality levels defined by the final product specifications. For more demanding terrain we can now be fully confident that the second (and partially third) coverage will deliver a global, uniform DEM with unprecedented quality.”
During this first acquisition campaign the experts at Astrium and DLR also gained valuable insight into the representation of different vegetation zones (e.g. rain forest, wetlands, etc.) in the stereo images. The different surface characteristics of these zones and thus the specific character of the returned radar signals can now be examined and analysed by radar specialists and will provide an enhanced understanding of synthetic aperture radar.
Comparing the Shuttle Radar Topography Mission (SRTM) elevation model from 2000 and the data acquired by TanDEM-X over
the opencast lignite mine at Hambach, near the German town of Jülich, the improved accuracy is impressively demonstrated.
In addition, the changes over the past 10 years can be seen—mining activity has progressed considerably. © DLR
Fully on schedule for the global DEM in 2014
The TanDEM-X mission concept is to complete the global uniform DEM in the shortest possible timeframe and have the full dataset available within just 3 years. To achieve this ambitious goal, the acquisition plan is optimised for time-efficient coverage of the Earth’s entire landmass. As a result, acquisitions are not recorded region by region but rather in the style of a jigsaw puzzle. Seemingly random acquisitions are made in different locations across the globe and as the jigsaw is completed, the overall picture emerges once all the pieces are assembled. This acquisition planning also means that the DEM will not be available on a regional basis but the global dataset will be completed in one go and made available to commercial and scientific users.
Following the first coverage, the two satellites are already continuing with the second coverage, which again will require approximately one year for completion. Selected more complex terrain areas will then be covered with a third acquisition campaign to ensure the consistently high quality and accuracy of the final product.
Upon completion of the complex data-processing task, the global TanDEM-X DEM will be available from 2014 onwards. And given the mission’s success so far, TanDEM-X is on course to meet this challenging goal.
TanDEM-X Mission Running Like Clockwork
Did you know?
Acquiring data in bi-static mode means that one satellite transmits radar pulses and both satellites record the backscattered signal. This means that one satellite is only “listening” to the ‘echo’ signals that come back from the ground, so one of the two satellites can save battery power and keep its radar instrument cool. In the case of TerraSAR-X and TanDEM-X, this is working so well that the mission is in very good shape regarding on-board resources (power and fuel) and DLR experts predict that the TanDEM-X mission can be extended by up to four years.