The new three-dimensional map of Earth has been completed. Mountain peaks and valley floors across the globe can now be seen with an accuracy of just one metre. The global elevation model was created as part of the TanDEM-X satellite mission; it offers unprecedented accuracy compared with other global datasets and is based on a uniform database. The approximately 150 million square kilometres of land surface were scanned from space by radar sensors. “TanDEM-X has opened up a whole new chapter in the field of remote sensing. The use of radar technology based on two satellites orbiting in close formation is still unique and was key to the high-precision remapping of Earth. In this way, DLR has demonstrated its pioneering role and satisfied the prerequisites for the next major development step in satellite-based Earth observation – the Tandem-L radar mission,” says Pascale Ehrenfreund, Chair of the Executive Board of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR).
(The first TanDEM-X mosaic of Iceland. Credit: DLR)
The quality of the global elevation model has surpassed all expectations. Exceeding the required 10-metre accuracy, the topographic map has an elevation accuracy of a single metre. This is a result of excellent system calibration. The distance between the two satellites in formation flight, for example, is determined with millimetre precision. The global coverage achieved by TanDEM-X is also unparalleled – all land surfaces were scanned multiple times and the data was then processed to create elevation models. In this process, DLR’s remote sensing specialists created a digital world map consisting of more than 450,000 individual models with pixel by pixel height detail – creating a special kind of three-dimensional mosaic.
TerraSAR-X and TanDEM-X have long exceeded their specified service lives and continue operating faultlessly and in such an efficient way that they still have enough propellant for several more years. Completion of the 3D world map does not signify the end of the mission. Due to the special nature of the formation flight, further scientific experiments are scheduled. Moreira points out: “Earth as a system is highly dynamic, which is also reflected in its topography. Through frequent updates, we could capture such dynamic processes systematically in the future. This is the primary goal of the Tandem-L mission that we have proposed.” (Image 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 – the mining activity has progressed considerably.)
New Synthetic Aperture Radar (SAR) methods will enable diverse data for exploration of the global ecosystem to be provided within short periods of time. The Tandem-L successor mission could provide a current elevation image of Earth’s entire landmass every eight days and thereby capture dynamic processes in a timely manner. This would also make it possible to contribute to the review of international climate and environmental agreements. New radar methods and innovative missions such as Tandem-L are set to contribute to gaining a better understanding of dynamic processes in order to protect and preserve Earth Completion of the TanDEM-X global elevation model has now paved the way for the next dimension of radar remote sensing.
About the mission
TanDEM-X is being implemented on behalf of DLR using funds from the Federal Ministry for Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie). It is a Public Private Partnership (PPP) project operated in conjunction with Airbus Defence and Space. DLR is responsible for providing TanDEM-X data to the scientific community, mission planning and implementation, radar operation and calibration, control of the two satellites, and generation of the digital elevation model. To this end, DLR has developed the necessary ground-based facilities. The DLR Microwaves and Radar Institute, the DLR Earth Observation Center and the DLR Space Operations Facility in Oberpfaffenhofen are participating in the development and operation of the ground segment of TerraSAR-X and TanDEM-X. Scientific coordination is the responsibility of the DLR Microwaves and Radar Institute. Airbus Defence and Space built the satellites and is sharing the development and operating costs. The company is also responsible for the commercial marketing of the TanDEM-X data.