TanDEM-X - the Earth in three dimensions
Satellite twins TerraSAR-X and TanDEM-XThe satellite twins TerraSAR-X and TanDEM-X fly in close formation – sometimes separated by only a few hundred metres – and thus acquire data for digital elevation models.
The objective of the TanDEM-X mission (TerraSAR-X add-on for Digital Elevation Measurement) is to produce a highly accurate, three-dimensional image of our Earth with uniform quality and unprecedented accuracy. For large parts of the earth, only rough, non-uniform or incomplete elevation models from different data sources and survey methods existed before the mission began. The previous maps therefore often have breaks, for example at national borders, or they are difficult to compare because they were created with different measurement methods and time-staggered measurement campaigns. TanDEM-X closes these gaps and provides a homogeneous elevation model as an indispensable basis for many commercial applications and scientific questions.
For this purpose, two almost identical satellites orbit the earth at an altitude of around 500 kilometres and scan the surface with radar equipment. The first of the two satellites, TerraSAR-X, has been operating successfully in space since 2007. Since 2010, it has been followed by the almost identical satellite TanDEM-X. Both fly only a few hundred metres apart in close formation, thus enabling the simultaneous imaging of the terrain from different angles. From this, precise elevation information is derived in a 12-metre grid and with a vertical accuracy of better than two metres.
The TanDEM-X Mission
TanDEM-X and TerraSAR-X form the first configurable SAR interferometer (SAR = Synthetic Aperture Radar) in space. The TanDEM-X satellite is a replica of TerraSAR-X with minor extensions. It has an additional cold gas propulsion system and can therefore fine-tune its orbit for formation flight with TerraSAR-X. TanDEM-X also receives attitude and position data from its twin satellite. Since SAR systems actively "illuminate" the earth's surface with its radar signals, measurements can be carried out around the clock, independent of daylight. In addition, SAR systems are largely independent of weather conditions, as the radar signals are able to penetrate clouds. Compared to optical sensors, images of the earth's surface can therefore be taken at any time. This contributes significantly to the reliability of the entire system, a feature that is increasingly demanded by many users.
In the period from 2011 to 2015, both satellites have surveyed the entire land surface of the Earth, i.e. 150 million square kilometres, several times completely in order to ensure the main objective of the mission, the creation of the global Digital Elevation Model (DEM). The global TanDEM-X terrain model has a grid size of 12 meters × 12 meters and has a high vertical accuracy, which is mostly better than 2 meters. Furthermore, it is homogeneous throughout and thus forms the basis for a globally uniform map material.
The production of the global terrain model from the acquired data set of both satellites was completed in September 2016. About 3 petabytes (equivalent to 3000 terabytes) of data were processed into the final digital 3D map product, which is now available in the form of 19,000 tiles. Each tile represents an area of 1° × 1° (longitude × latitude), corresponding to about 100 km × 100 km near the equator. The global TanDEM-X terrain model is also available in different product variants with a grid size of 12 m, 30 m and 90 m.
The three-year acquisition phase for the global elevation model was followed by an acquisition phase to explicitly serve scientific needs such as forest mapping, snow and ice detection, observation of volcanoes, urban areas, ocean currents and the demonstration of new radar techniques to develop new applications.
If the earth's surface is analysed with the accuracy of TanDEM-X, it can be clearly seen that this is an extremely dynamic system. Not only altitude changes in glaciers, permafrost areas and forests, but also agricultural activities and changes in infrastructure leave clear traces in the digital terrain model. Therefore, since September 2017 a further complete survey of the Earth's landmass has been carried out in order to obtain another independent and unique data set. The resulting product, called "Change DEM", will make it possible to track topographic changes worldwide.
A German key project
Following in the footsteps of European radar satellites ERS-1, ERS-2, Envisat and TerraSAR-X, as well as the joint US-German-Italian Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew on the Space Shuttle and the US Shuttle Radar Topography Mission, TanDEM-X seeks to support scientific and commercial applications of radar-based Earth observation. Demonstrating Germany's expertise in satellite-based radar technology, the mission is the result of a long-term focus in Germany's national space programme.
TanDEM-X was launched on behalf of DLR as a public-private partnership (PPP) project with Airbus Defence and Space (formerly Astrium) with funding from the German Federal Ministry of Economics and Energy (BMWi).
DLR is responsible for the scientific use of the TanDEM-X data, the planning and execution of the mission, the control of the two satellites and the generation of the digital elevation model.
Airbus Defence and Space built the satellite and contributes to the development and utilisation costs. As with TerraSAR-X, the "Geo-Intelligence" programme line is responsible for the commercial marketing of the TanDEM-X data. Since 2016, the project has been continued under a continuation agreement with Airbus.
|TanDEM-X quick facts|
|Launch:||21 June 2010, 04:14:03 CEST|
|Launch site:||Baikonur (Kazakhstan)|
|Orbit altitude:||514 kilometres|
|Orbit inclination:||97.4 degrees|
|Satellite mass:||1330 kilograms|
|Satellite dimensions:||Height: 5 metres|
Diameter: 2.4 metres
|Power consumption:||730 watts (average)|
|Mission operation:||German Space Operations Center, Oberpfaffenhofen|
|Satellite command:||Weilheim ground station|
|Data reception:||Ground stations:|
- Inuvik, Canada
- O'Higgins, Antarctic
- Kiruna, Sweden
|Satellite lifetime:||5.5 years (6.5 years for consumables)|
|Radar centre frequency:||9.65 gigahertz (X-band)|
The mission involves the DLR Microwaves and Radar Institute, the DLR Remote Sensing Technology Institute and the DLR German Remote Sensing Data Centre, who jointly form the "SAR Centre of Excellence". The institutes complement each other by covering all relevant fields from sensor technology and mission design to high-precision operational processing and value-added end-user products. Together with DLR's German Space Operations Centre, they are also responsible for setting up the ground segment respectively the infrastructure for operating the satellites and processing the data. The DLR Microwaves and Radar Institute in Oberpfaffenhofen is responsible for scientific coordination.
Earth Observation - Discovering, surveying and understanding our planet.Life today is much more about knowledge than it was a generation ago. Global change, a sustainable development of our habitats, an efficient use of resources, securing our mobility and our competitive position in the world of
Tidal glaciers in Greenland – TanDEM-X elevation models show strongest decline in 80 yearsThe Kangerlussuaq Glacier is the largest glacier on the southeast coast of Greenland and flows into the fjord of the same name. The glacier front, which in the past was protected by an ice mélange – a mixture of sea ice and calved icebergs – is retreating at an increasing rate.
TanDEM-X reveals glaciers in detailA precise understanding of glacier evolution requires knowledge of a glacier's exact mass. This is important in South America, in the tropical regions between Bolivia and Venezuela, where meltwater from glaciers provides drinking water during the dry season.
Global TanDEM-X forest map is available.Forests are Earth's lungs; they help to reduce greenhouse gas concentrations in the atmosphere and thus counteract global warming, while also providing protection and resources for humans, animals and plants – and they are being lost at an alarming rate. As the view from space reveals, forests cover about one third of Earth’s landmass today. More than half of the world’s forests, which have fallen victim to deforestation since the middle of the 20th century in particular, have already been lost.
Waves on the ice – Canadian 'ice road' trucks in TanDEM-X's 'radar eye'Ice road truckers in Canada – symbolically 'at the end of the world' – with their massive trucks travelling over the frozen lakes in the Canadian northwest, are well known around the world thanks to numerous TV programmes. The ice roads are open for only a few weeks per year.
Big Data from Space – seeking solutions for the flood of data from spaceEarth observation satellites provide important data that allows the rapid detection of changes to the environment and climate, for example, or measurements of the movement or shrinking of glaciers. Up-to-date maps can be provided to the emergency services in the event of disasters such as flooding or earthquakes.
Glacier retreat in Antarctica – innovative radar technologies enable improved predictionsThwaites Glacier, one of the most fragile glaciers in western Antarctica, is melting inexorably into the Amundsen Sea at an ever-increasing rate. Until now, it has been responsible for approximately four percent of the global rise in sea level and will cause the oceans to rise by over 65 centimetres in future as its remaining ice melts.
Global 3D elevation model from the TanDEM-X mission now freely availableThe 90-metre TanDEM-X Digital Elevation Model has been released for scientific use and is now available as a global dataset. By providing this data, the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) follows the EU data policy under the Copernicus Earth observation programme, which encourages free and open access to satellite data.
PAZ Earth observation satellite successfully launchedThe Spanish Earth observation satellite PAZ was successfully launched on 22 February 2018 at 15:17 CET from Vandenberg Air Force Base in California, United States, on board a Falcon 9 rocket. Interestingly, PAZ is being positioned on the same orbit as the German TerraSAR-X and TanDEM-X radar satellites.
The future of radar – scientific benefits and potential of TerraSAR-X and TanDEM-XThe German satellite duo TerraSAR-X and TanDEM-X have consistently delivered one-of-a-kind Earth observation data since 2007 and 2010, hence shaping the international research landscape. Now, scientific users from across the globe have gathered for the TerraSAR-X and TanDEM-X Science Meeting at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) in Oberpfaffenhofen, where they will discuss the results obtained from the data and define requirements for future remote sensing technology.
New 3D world map – TanDEM-X global elevation model completedThe 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.
Elke HeinemannGerman Aerospace Center (DLR)Public Affairs and CommunicationsTelephone: +49 2203 601-2867
Fax: +49 2203 601-3249
Dr.-Ing. Stefan BuckreußMission Manager TerraSAR-X / TanDEM-XGerman Aerospace Center (DLR)Microwaves and Radar InstituteTelephone: +49 8153 28-2344
Fax: +49 8153 28-1449Münchener Straße 20Contact