资源环境科技发展态势分析平台

Fifteen years – who would have thought it? The German radar satellite TerraSAR-X, which was launched from the Baikonur Cosmodrome in Kazakhstan at 08:14 local time on 15 June 2007, was originally designed to last five and a half years – until the end of 2012. It has been delivering data of outstanding quality ever since, regardless of weather conditions, cloud cover and daylight levels. The scientific mission for TerraSAR-X and the satellite itself are operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR).

As it turns 15, TerraSAR-X can look back on 83,050 orbits of Earth, having travelled approximately 3.59 billion kilometres – a vast distance. If the satellite were travelling away from Earth in a straight line, it would have crossed the orbit of Uranus by late 2018 and would now be roughly midway between the orbits of Uranus and Neptune. At the grand old age of 15, TerraSAR-X is still in perfect shape.

Thanks to its robust design, combined with the highest measurement accuracy and stability, the satellite is still providing radar images that far surpass the original requirements for the mission. The high-resolution data and continuous view provided by TerraSAR-X enables researchers from all over the world to document and better understand the changes taking place on Earth, while facilitating the early detection of irreversible damage and pinpointing where intervention is needed. Such data provides an essential foundation for developing measures at a political and social level.

A data repository and research subject

Over its lifetime, TerraSAR-X has acquired more than 400,000 radar images, collecting 1.34 petabytes of data in the process. This is equivalent to 1,340,000 gigabytes or the streaming of around 270,000 high-definition feature films, which would take around 60 years to run through. The satellite’s legacy is becoming more comprehensive, more valuable and more widely used every day. More than 1100 leading researchers from 64 countries are now drawing upon and processing its data as part of 1875 ongoing research projects. Not only does the range of applications encompass the full spectrum of geosciences, including geology, glaciology, oceanography, meteorology and hydrology, but the radar data are also essential for environmental research, land use mapping, vegetation monitoring, and urban and infrastructure planning. Cartography, navigation, logistics, crisis management and defence and security also rely on TerraSAR-X data.

The satellite itself is the subject of research and development as well, particularly in the field of radar technology. With its flexible design, the radar system enables experiments to be conducted using new imaging modes such as a 'super wide angle' and 'super zoom', similar to a camera being fitted with different lenses. Officially referred to as 'WideScanSAR' and 'Staring Spotlight Mode', these were introduced during the course of the mission and then made available to users. The satellite continues to conduct radar experiments to test new techniques that might be used on future radar missions.

A third dimension with TanDEM-X

Since 21 June 2010, TerraSAR-X has been accompanied by the TanDEM-X satellite, which is almost identical in design. TanDEM-X and TerraSAR-X form the first reconfigurable Synthetic Aperture Radar (SAR) interferometer in space, recording precise height information for creating digital elevation models. This means that TerraSAR-X is now being used for two missions – the original TerraSAR-X mission and the TanDEM-X mission for three-dimensional mapping of Earth’s surface.

Despite its unprecedented longevity, the day will eventually come when TerraSAR-X is no longer able to fulfil its tasks. Resources such as propellant and battery capacity are steadily being depleted. However, if there are no major incidents, TerraSAR-X could remain in operation until the end of the 2020s.

Environmental observation in future – Tandem-L

With the TerraSAR-X and TanDEM-X satellite missions, DLR has set new standards in radar remote sensing. Its experts are already working on the next generation of radar satellites for climate research and environmental monitoring, in the form of Tandem-L, a highly innovative radar satellite mission. This could see Germany provide a system for the objective recording of the environment and the observation of environmental changes all over the world. The goal is to provide critical information to tackle highly relevant issues. For example, the latest report by the Intergovernmental Panel on Climate Change (IPCC) calls for the development of climate protection measures and the review of measures taken on a global scale, as a matter of urgency.

With Tandem-L, it would be possible to record a large number of dynamic processes in the biosphere, geosphere, cryosphere and hydrosphere with unprecedented quality and resolution. The new satellite constellation could provide up-to-date 3D imaging of Earth's entire landmass on a weekly basis and measure seven essential climate variables simultaneously. In doing so, Tandem-L would make a significant contribution towards a better understanding of processes that are now seen as drivers of local and global climate change.