Le Bourget 2007 – This June, the German Earth observation satellite TerraSAR-X will be launched from the Russian cosmodrome in Baikonur. Orbiting the Earth at an altitude of approximately 514 kilometres, the satellite will use a radar beam to scan the planet’s surface – regardless of weather conditions, cloud cover or daylight – and deliver fast and reliable data for a wide range of applications, producing a completely new range of options for commercial, public and scientific users. TerraSAR-X is the first national remote sensing satellite to be realised within the scope of a Public Private Partnership (PPP): Astrium developed and built the spacecraft under contract to the German Aerospace Center DLR, and also made a significant capital contribution of its own. The data and products will be marketed by Infoterra, a subsidiary of Astrium. TerraSAR-X is expected to have a working life of five years; its successor, TerraSAR-X2, is already in the planning stages. Also on the agenda is the construction of a partner satellite called TanDEM-X, which will orbit the Earth alongside TerraSAR-X. The pair will create a digital elevation model of the entire planet with a degree of resolution never before attained.
Commercial exploitation requires high-quality data
The demand for premium-quality images of our planet has risen considerably in recent times. While the pursuit of scientific knowledge was the key factor motivating early Earth observation activities, commercial interests are now increasingly coming to the fore.
This progression from purely scientific endeavours towards commercial and public applications has led to calls that the responsibility for gathering Earth observation data be transferred to private enterprise. This is expected to result in the development of a sustainable business segment that will benefit all participants. But the success of commercial exploitation will be contingent upon the availability of very high quality data that are rich in detail and can be delivered promptly and reliably.
The green light for TerraSAR-X came with the signing of a cooperation agreement on 25 March 2002, in which DLR awarded the €102 million contract for development, construction and launch to EADS Astrium. The space company added €28 million of its own resources and also financed development and marketing of the geo-information products. DLR has since established the ground segment for data reception and satellite command, and will also process, archive and distribute the data. Astrium built and tested the satellite, while its subsidiary Infoterra has already obtained pre-launch sales and marketing partners for data products and negotiated the first contracts with future customers.
Active radar with zoom
After being launched on a Russian-Ukrainian Dnepr 1 rocket (formerly an SS 18 ICBM), TerraSAR-X will orbit the Earth about once every 95 minutes at an altitude of about 514 kilometres. Because of the Earth’s continued rotation during the course of each orbit, the radar will be able to scan every point on the surface of the planet within a period of no more than four days, with 95 per cent of these cycles occurring within just two days.
TerraSAR-X will scan the Earth using a technology called Synthetic Aperture Radar (SAR). Radar holds several decisive advantages over imaging in the visible light range: a radar beam creates its own source of illumination that always remains precisely defined. This is not the case with optical satellite photos, in which the position of the sun can exert considerable influence on a landscape’s appearance. Radar also works day and night, and can scan through clouds. “This is especially important for areas near the equator, where it is quite frequently cloudy,” explains Wolfgang Pitz, TerraSAR-X Project Manager at Astrium in Friedrichshafen.
A further distinguishing feature is the variant of radar technology employed by the satellite, called active radar. Active in this case means that the beam can be angled within a slewing range of 20 to 60 degrees. This is not achieved through mechanical movement of the antenna or of the entire spacecraft, but rather by selectively superimposing multiple individual radar beams. This method expands the area that can be imaged by the instrument. “Whereas we can record a maximum of two images during an overflight from Munich to Berlin using a passive radar, it is now possible to take up to 20,” says Pitz.
Also contributing to the wide diversity of potential applications is the ability to choose three different levels of resolution and image size. This ‘zoom’ function allows details to be observed at a resolution of 16 metres with an image swath of 100 km in ScanSAR mode, with a resolution of 3 metres (30 km swath) in StripMap mode, and even as high as 1-metre resolution (5 x 10 km swath) in Spotlight mode.
Engineers and technicians at Astrium were only able to achieve such an extremely high degree of image resolution by using so-called X-band radar. The radio signals emitted by the TerraSAR-X radar are transmitted at a frequency of 9.65 gigahertz, which corresponds to a wavelength of around three centimetres. In contrast, many previous satellites operated in the C- or L-band, with larger wavelengths of 5.7 and 24 centimetres respectively – and thus delivered images with lower resolutions.
However, X-band technology is much more demanding in terms of the properties of materials used and the processing accuracy. Astrium can draw on years of experience in this area, know-how that was put to the test during previous scientific projects such as the SIR-C/X-SAR mission in 1994 and the Shuttle Radar Topography Mission (SRTM) in 2000. “X-band technology has always been a German speciality,” comments Pitz. “In this field, we are at the leading edge worldwide.”
The aforementioned features also explain the derivation of the satellite’s name: Earth (Terra) observation with Synthetic Aperture Radar (SAR) in the X-band (X).
A wide variety of applications
The wealth of information contained in radar data can be processed to suit the specific needs of any potential user. TerraSAR-X will benefit not only the commercial sector but also government agencies and scientific establishments. Infoterra GmbH, a wholly owned subsidiary of Astrium, will be responsible for marketing the commercial data. As a representative of the German federal government, DLR will retain ownership of the data and coordinate their scientific use.
Future users will be able to choose between two options – Direct Access Partner (DAP) and Direct Access Customer (DAC) – and will sign a contract with Infoterra that allows them to receive the data at their own ground station. Other commercial users will purchase processed data from Infoterra via a secure Internet portal or by phone. Scientists will be able to obtain data records from DLR free of charge for selected research projects.
TerraSAR-X opens up a broad range of applications. The system’s ability to operate regardless of cloud cover, for instance, makes it possible to rapidly generate an up-to-date map of large areas, in particular extensive forest and mountain regions. Many countries are also interested in quantifying forested resources and forest biomass. TerraSAR-X data could also be used as a German contribution to the Global Monitoring for Environment and Security (GMES) initiative, a European action plan that combines data from terrestrial, maritime and space-based measuring systems.
One of the application fields for TerraSAR-X data is reconnaissance. Intelligence services, reconnaissance aircraft and relief organisations can benefit from systems that not only offer very high resolution but also provide timely data acquisition. These organisations typically rely on data gathered by optical sensors, which in some cases may mean waiting a long time. Data acquisition in near real-time, as is possible with TerraSAR-X, offers these customers unprecedented opportunities to use satellite data in time-critical situations.
Government organisations will also benefit from TerraSAR-X data. Land survey offices, for example, will be able to catalogue structural and other changes in their communities on a regular basis, or rapidly and cost-effectively take stock of wind-damaged areas in the aftermath of a hurricane. Accurate, up-to-date maps make it easier to coordinate humanitarian aid projects and subsequent reconstruction efforts following natural disasters in every corner of the world. And radar maps can also be used for strategic reconnaissance and troop deployment in conflict zones. “We will gain considerable experience in our first year of operation, undoubtedly coming across applications along the way that we haven’t even thought of yet,” says Jörg Herrmann, Managing Director of Infoterra GmbH. New commercial applications are likely to evolve from the scientific projects under the aegis of DLR.
A further TerraSAR-X speciality, the Dual Receive Antenna Mode, will foster the development of completely new applications. In this mode, two independent antenna elements work like a pair of eyes, making it possible to discern movement on the ground. This capability will be used to attempt to measure the speed of cars on motorways. One long-term goal of this sort of technology could be a multi-satellite system for monitoring and controlling traffic flow.
The future has already begun: TerraSAR-X2 and TanDEM-X
The declared goal of the TerraSAR-X project is sustainability. Its underlying purpose is not to conduct a one-time survey of the Earth, but rather to monitor it continuously. The orbiting radar is intended to become a regular, operational system, just as weather satellites have been for some time now. With a view to this objective, the course has already been set for its successor. TerraSAR-X2, which is to be financed from the profits realised by Infoterra from TerraSAR-X images, is scheduled for launch in 2012.
But development continues unabated, and there are still many applications for TerraSAR-X technology. Astrium is therefore preparing to implement the TanDEM-X project (TerraSAR-X add-on for Digital Elevation Measurement) on behalf of DLR. This consists of an additional satellite, similar in construction to TerraSAR-X, that will fly alongside TerraSAR-X at a distance of between 500 metres and two kilometres. Applying the same principle that endows humans with depth perception, the addition of TanDEM-X as a second ‘eye’ could record a three-dimensional elevation model of the entire Earth. This would even make it possible to follow movement patterns such as ocean currents. TanDEM-X will also be financed under the PPP model, and could be launched in March 2009.
About Astrium:
Astrium, a wholly-owned subsidiary of EADS, specialises in civil and military space systems. In 2006, the company recorded sales of €3.2 billion and employed a staff of around 11,000 in France, Germany, the UK, Spain and the Netherlands.
Its core business is divided into three areas: the Astrium Space Transportation Business Unit for launch vehicles and space infrastructures; the Astrium Satellites Business Unit for satellites and ground segments; and the wholly-owned subsidiary Astrium Services for development and delivery of satellite-based services.
EADS is a worldwide leader in aerospace, defence, and related services. In 2006, the company achieved a total turnover of around €39.4 billion, employing a staff of over 116,000.
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TerraSAR-X at a glance
Length: 4.88m
Diameter: 2.4m
Launch weight: 1230 kg
Payload weight: approx. 400 kg
Radar frequency: 9.65 GHz
Power consumption: 800 watts (average)
Resolution: 1m, 3m, 16m (depending on image size)
Launch vehicle: Dnepr 1 (formerly SS-18)
Launch site: Baikonur, Kazakhstan
Orbital altitude: 514 km
Inclination: 97.4° (sun synchronous)
Life span: at least five years
TerraSAR-X is the first German satellite to be realised within the scope of a public-private partnership (PPP) between DLR and Astrium: Europe’s leading satellite specialist, Astrium, is sharing the costs of the development, construction and deployment of the satellite. The scientific use of the TerraSAR-X data is the responsibility of DLR, whilst Infoterra GmbH, a subsidiary of Astrium, will be responsible for the commercial marketing of the satellite data. With its active antenna, the satellite will record new high-quality X-band radar images of the entire planet whilst circling Earth in a polar orbit at an altitude of 514 kilometres. Able to work independently of weather conditions, cloud cover or daylight, TerraSAR-X will be able to provide radar images with a resolution as high as one metre.
