TerraSAR-X marks two successful years in orbit
Friedrichshafen. - TerraSAR-X, the German radar satellite, has completed two successful years of service since its launch on 15 June 2007. In contrast to optical systems, its radar technology has allowed the generation of images even in cloudy or night time conditions, thus ensuring that the satellite has operated non-stop. TerraSAR-X is Germany’s first radar satellite and, at the same time, the first national remote sensing satellite which has been implemented in a Public-Private Partnership (PPP) between the German Aerospace Centre (DLR) and Astrium in Friedrichshafen. DLR is responsible for planning and implementing the mission, controlling the satellite and the radar instrument, as well as for the scientific exploitation of the data from the new TanDEM-X satellite, which is due to be launched later this year.
Shortly after TerraSAR-X’s launch from the Russian Space Centre in Baikonur, DLR were able to present the first images from the satellite in just four days. Subsequently, commissioning of the satellite and the radar instrument were completed as planned, with the satellite becoming fully operational in early 2008. Since then, the mission has been characterised by a smooth operation and production process, generating a variety of unique imaging products, which have been used for both scientific and commercial purposes.
The launch of the TanDEM-X radar satellite, which is almost identical in construction, is scheduled for October 2009. Orbiting in a close formation with TerraSAR-X, at distances of between a few kilometres to just 200 metres, the two satellites will be able to capture data of unprecedented accuracy. This will ultimately lead to a global digital elevation model of all land masses on the Earth’s surface.
Successful two-year results with excellent geolocation accuracy
Since the launch of the TerraSAR-X satellite, the Mission Control Centre of DLR has successfully planned, commanded and executed approximately 35,000 radar images of the Earth’s surface and processed them into about 50,000 high-quality products for scientific and commercial users. The existing results impressively demonstrate the high quality of the TerraSAR-X products which, in many areas, even exceed the requirements. What has been of particularly impressive is the outstanding geolocation accuracy of better than 0.5 metres. This allows fully automatic, pixel-accurate superposition of two images of a scene acquired at different times. Further features are the high radiometric accuracy and the excellent radar instrument stability.
Various scientific and commercial applications due to radar technology
TerraSAR-X products can be used for numerous scientific and commercial applications. The main focus is on land applications, such as agriculture and forestry, land use/vegetation, observation of rural areas and cartography. Ice research and maritime applications have also benefited from the radar data. Three examples for the variety of applications are shown in the following.
Fast help from space in the case of natural disasters
Following natural disasters, TerraSAR-X data has been repeatedly used by international authorities for on-site crisis management support. This includes the mapping of flood areas and damage assessment after earthquakes. In early November 2007, heavy rainfall lasting for weeks led to devastating floods in the Mexican states of Tabasco and Chiapas, displacing about one million people and approximately half of Tabasco’s overall population. About 80% of the state of Tabasco’s surface, i.e. an overall area of approximately 25,000 square kilometres, was temporarily flooded. The DLR centre for satellite-based crisis Information (ZKI) supported the Mexican civil protection authority (CENAPRED) with satellite image maps of the floods. Capable of operating in cloudy conditions or at night time, TerraSAR-X is able to deliver high resolution imagery with a resolution of up to one metre.
Early detection of changes and climate influences in the Antarctica
With the help of the TerraSAR-X satellite, scientists have observed the loss of a huge ice bridge on the Antarctic Wilkins Ice Shelf. There, the first icebergs broke away on 20 April 2009 and the TerraSAR-X images show this development. These icebergs are breaking away at the failure zones which have gradually formed over the past 15 years. The high resolution of the TerraSAR-X satellite images enables the observation of deformations in the Wilkins Ice Shelf, down to a range of approximately 100 metres. This information enables the glaciologists to describe distortion more precisely with the help of models. Newly formed cracks are very narrow during their initial stages and are therefore not visible on images taken at a lower resolution, such as those supplied by the older generation of satellites. To reconstruct the chronological sequence of events, the kind of high-resolution images supplied by TerraSAR-X are necessary.
Weather-independent and cross-border traffic information via satellite - for traffic forecasting and better route suggestions
DLR has begun several months of tests into the feasibility of obtaining traffic information via satellite. TerraSAR-X is going to monitor selected motorway sections in Germany, Austria, Switzerland and California. The aim of this project is to develop a procedure for large-scale traffic data capture, independent of ground systems, which will permit the relay of data to various traffic information providers. In contrast to measurement procedures currently used, which are mostly stationary procedures, information gleaned by satellite can yield up-to-the-minute information, even from roads without sensors, whatever the weather, regardless of borders. The technology is not limited to discovering areas of high traffic density. It can also be used to calculate the average speed of motorway traffic, so that the exact journey time between junctions can be established. With the help of such information, traffic information service providers will be able to make better route suggestions – even in fog, heavy rain and darkness – thanks to the latest radar technology. However, the recognition of vehicle number plates is not possible with this technology.
The two add-on payloads also in successful operation
The secondary payloads of TerraSAR-X, i.e. the TESAT-built Laser Communication Terminal (LCT) and the Tracking, Occultation and Ranging (TOR) experiment provided by the geo-research centre (GFZ) are working perfectly. The LCT is a DLR financed technology demonstrator used for in-orbit verification of rapid optical data transfer in space. With the help of LCT, a reproducible data exchange between the two low-flying satellites, i.e. TerraSAR-X and NFIRE, could be obtained for the first time at a transmission rate of 5.5 gigabits per second.
Unique success story of the German radar satellite TerraSAR-X
Based on the experience gained in the first two years of operation, the TerraSAR-X mission can be considered to be an outstanding success story receiving recognition and appreciation from the US space agency NASA and other national space organisations, as well as the European Space Agency (ESA). For the coming years of operation, many more exciting results can be expected which will provide further scientific and commercial highlights.
Second TanDEM-X radar satellite scheduled for launch in October – providing third-dimension data
TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement), the second almost identical German radar satellite, has already been completed and is being extensively tested in Munich at Astrium and IABG. Its launch from the Russian Baikonur Space Centre is scheduled for October. By orbiting in close formation, the two satellites are to capture data of unprecedented accuracy for a global digital elevation model of all land masses of the Earth’s surface.
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