TerraSAR-X

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TerraSAR-X
Type: Earth observation satellite
Country: GermanyGermany Germany
Operator: German Aerospace CenterDLR DLR
COSPAR-ID : 2007-026A
Mission dates
Dimensions: 1230 kg
Size: Height 5 m, diameter 2.4 m
Begin: June 15, 2007
Starting place: Baikonur
Launcher: Dnepr
Status: active
Orbit data
Rotation time : 94.9 min
Track height: 514 km
Orbit inclination : 97.4 °
Apogee height :  530 km
Perigee height :  512 km

TerraSAR-X (“Terra”: Latin for the earth, SAR: Synthetic Aperture Radar , “X” for the X frequency band [microwaves, 8-12.4 GHz]) is a German earth observation satellite that operates under a public-private -Partnership (PPP) between DLR and Airbus Defense and Space was realized. Airbus Defense and Space GmbH holds the exclusive commercial rights of use. TerraSAR-X was launched on June 15, 2007 and began operations in January 2008.

With its active phase-controlled antenna (wavelength 31 mm, frequency 9.65 GHz), TerraSAR-X acquires new, high-resolution radar data while it circles the entire earth in an almost polar orbit at an altitude of 514 km. The orbit is chosen so that the satellite flies in a sun-synchronous dusk-dawn orbit. This means that the satellite flies along the earth's day-night boundary and always faces the same side of the sun. This serves in particular for an optimal energy supply by the solar cells. TerraSAR-X can reliably record radar data with a resolution of up to 1 m regardless of weather conditions and lighting conditions and has a service life of at least 5 years.

Features of TerraSAR-X

  • Geometric resolution of up to 1 m
  • Good radiometric accuracy (high signal-to-noise ratio)
  • Mapping of any point on earth within max. 2.5 days (by changing the perspective)
  • High flexibility (quick switching between recording modes and polarizations)

TerraSAR-X acquisition modes

TerraSAR-X acquires radar data in the following three main recording modes:

High Resolution SpotLight
Up to 1 m resolution, scene size 10 km (width) × 5 km (length)
StripMap
Up to 3 m resolution, scene size 30 km (width) × 50 km (length *)
ScanSAR
Up to 18 m resolution, scene size 100 km (width) × 150 km (length *)

(* StripMap & ScanSAR: the length of the recording can be extended up to 1650 km. The recording strip is delivered in the above-mentioned scene sizes.)

In addition, the unique design of the TerraSAR-X-SAR antenna enables a large number of polarimetric combinations: single or dual polarization and even fully polarimetric data sets are possible.

Depending on the desired application, one of four different product types (processing levels) can be selected

  • Single-Look Slant Range Complex (SSC)
  • Multi Look Ground Range Detected (MGD)
  • Geocoded Ellipsoid Corrected (GEC)
  • Enhanced Ellipsoid Corrected (EEC)

Advantages of radar technology

RADAR stands for Radio Detection and Ranging and traditionally includes:

  • Distance measurement (EDM) by measuring the transit time of reflected signals,
  • Direction measurement via the alignment of the antenna, and more recently
  • also other analyzes such as SAR, polarization, interferometry etc.

Compared to optical camera systems, satellites with radar technology are still relatively new. The resolution (sharpness of detail) is generally lower, but radar has other advantages: Radar is independent of lighting and weather conditions, so that images can be acquired at any time of the day or night and regardless of cloudiness. This contributes significantly to the reliability of the system, a property that is required for many applications and users.

Early radar satellite techniques were e.g. B. Altimetry (height measurement above the sea), Seasat (NASA, started in 1978), determination of waves / wind or ground data. Nowadays, for example, we can measure the speed of other satellites and the slow deformation of volcanoes with an accuracy of mm / s ( GRACE ). The military has used radar since the late 1930s and radar satellites since at least 1978.

Innovations at TerraSAR-X

TerraSAR-X has some technical and scientific innovations. One of these innovations is a kind of zoom, with which the resolution can be changed in inverse proportion to the scanning area in a ratio of 1:10. Either a larger area with low resolution or a smaller area with high resolution can thus be recorded.

Furthermore, the antenna beam can be aligned within an angular range via the antenna electronics and thus the viewing angle can be changed (see phased array antenna ). Earlier radar satellites could only emit the antenna beam in one direction.

Another innovation that was successfully tested on both the German TerraSAR-X and the US NFIRE satellite is the Laser Communication Terminal (LCT), which was developed by Tesat-Spacecom in cooperation with DLR. These two Tesat LCTs in Low Earth Orbit (LEO) were used for a joint campaign by the US Department of Defense and the German Defense Ministry. After performing numerous LEO inter-satellite connections in various configurations, the LCTs transmitted hundreds of terabytes of 5.6 Gbit each way in varying ranges up to 5500 km away. LCT in-orbit operations and link management with Optical Ground Stations (OGS) have been successfully tested in complex scenarios with various S / C ground control networks.

Scan and train

Thanks to the swiveling radar - together with other refinements (precession of the earth flattening) - any place on earth can be observed within one to three days. For a certain point on earth, TerraSAR-X has a cycle of 11 days in order to reach exactly this point again with the same recording geometry. However, the same point with a different recording geometry (e.g. different angle of incidence or viewing direction) can be recorded again more quickly. The time is reduced towards the poles; Northern Europe, for example, typically has a cycle of three to four days until the selected point is reached again.

Ground segment

The mechanisms and controls for TerraSAR-X that operate on the ground were developed by DLR in Oberpfaffenhofen. It consists of the Mission Operating Equipment, the Payload Ground Segment and the Instrument Operation and Calibration Segment. At the base of the ground segment are the German Space Control Center (GSOC), the German Remote Sensing Data Center (DFD) as well as the Institute for Remote Sensing Methodology (MF) and the Institute for High Frequency Technology and Radar Systems (HR), all of which are part of the DLR. Furthermore, there is the service segment of Infoterra GmbH, which is responsible for the distribution of TerraSAR-X data for commercial customers and manufactures and also sells higher quality products and services based on TerraSAR-X data.

Applications

Applications of the high-resolution TerraSAR-X radar images are:

  • Topographic mapping: 2D and 3D, at scales up to 1: 25,000, map updates
  • Movements of the earth's surface: Based on time series recorded by TerraSAR-X over the same area, movements of the earth's surface caused by mining, oil / gas production, civil engineering work or excavations can be visualized.
  • Change analyzes: for the monitoring of large construction projects, infrastructure networks as well as the monitoring and documentation of changes and developments
  • Land cover and land use mapping: accurate and up-to-date land cover / land use data, including areas that are difficult to monitor with other technologies due to permanent cloud cover.
  • Defense and security applications : Areas of application in this area include the support of effective operational planning, a quick assessment of the effects of natural disasters and crisis situations, or improved monitoring of borders through border controls by revealing routes (changes) and moving objects
  • Rapid crisis deployment planning: TerraSAR-X is a reliable source of information in the event of natural disasters or crisis situations (e.g. earthquakes, floods, military conflicts, etc.), as any point on earth can be reached within one to three days. Providing reliable information for disaster management and deployment planning enables damage to populated areas and transport infrastructure to be assessed, priority areas to be determined and rescue operations to be coordinated efficiently.
  • Environmental protection applications , e.g. B. Monitoring of forest areas, flood risk management, geographic information on water quality.
  • Other applications currently being examined: traffic monitoring, maritime applications, study of vegetation and its change.

Scientific use of the TerraSAR-X data

The scientific use of the TerraSAR-X data is coordinated by DLR's TerraSAR-X Science Service System. The new high-quality data sets recorded by TerraSAR-X form the basis for a wealth of new research projects, for example in the areas of ecology, geology, hydrology and oceanography. The investigation of the smallest movements of the earth's surface (plate tectonics, volcanism, earthquakes) are further scientific areas of application.

In the film Palmyra - Discovery from Space (2013) of the ZDF series Terra X , it is illustrated how the satellite was started and used for the archaeological exploration of the legendary desert city of Palmyra , and among other things helped to discover previously unknown parts of the city.

Commercial use of the TerraSAR-X data

In order to guarantee the economic success of the mission, Astrium GmbH founded the wholly-owned subsidiary Infoterra GmbH in 2001, which takes over the commercial marketing of TerraSAR-X data and the geographic information products and services based on it. Infoterra GmbH was transferred to Airbus Defense and Space GmbH in 2017.

controversy

The opposition parties Bündnis 90 / Die Grünen and Die Linke criticize the fact that although the data released for non-commercial use belongs to the Ministry of Economic Affairs as the ministry in charge of DLR, the Ministry of Defense wants to buy the data again from EADS Astrium for 475 million euros.

Extension by TanDEM-X

TanDEM-X (TerraSAR-X add-on for digital elevation measurements) is a second, almost identical radar satellite that has been flying parallel to TerraSAR-X since October 2010 at a distance of only 200 meters. This unique tandem satellite constellation provides the data basis for the global digital elevation model WorldDEM , which is unique in its combination of quality, accuracy and coverage.

Other SAR satellites

Examples

Web links

Commons : TerraSAR-X  - collection of images, videos and audio files

Individual evidence

  1. ^ W. Pitz and D. Miller, The TerraSAR-X satellite . IEEE Trans. Geosci. Remote Sens., Vol. 48, No. 2, pp. 615-622, Feb. 2010.
  2. ↑ R. Werninghaus and S. Buck Reuss, The TerraSAR-X mission and system design . IEEE Trans. Geosci. Remote Sens., Vol. 48, No. 2, pp. 606-614, Feb. 2010.
  3. ^ John R. Jensen: Remote Sensing of the Environment: An Earth Resource Perspective. Pearson, Upper Saddle River 2007, ISBN 978-0-131889507 .
  4. ↑ Laser Products | Tesat Spacecom. Retrieved January 12, 2018 .
  5. ↑ Terrasar-X exceeds all expectations. Press release from manufacturer EADS Astrium from 2007.
  6. ↑ GeoBerichte 14, State Office for Mining, Energy and Geology in Lower Saxony: Schrage, Thomas; Jacob, Philipp, June 2009, Land use and soil sealing in Lower Saxony.
  7. ^ GIM International: Balz, Timo; Scheuchl, Bernd; Li, Deren, October 2008, The Sichuan Earthquake (1) - Satellite Imagery for Rapid Response.
  8. ^ GIM International: Shao, Yun; Scheuchl, Bernd, November 2008, The Sichuan Earthquake (2) - Spaceborne SAR in Earthquake Response.
  9. ↑ GIM International: Koudogbo, Fifamè; Müller, Marc; Scheuchl, Bernd, December 2008, The Sichuan Earthquake (3) - Satellite-based Global Flood Response.
  10. ↑ TerraSAR-X Science Service System
  11. ^ ZDF: Palmyra - Discovery from Space , 2011.
  12. ↑ Markus Becker: Satellite images for the Bundeswehr: The mysterious 475 million euro deal. In: Spiegel Online. April 27, 2015, accessed on April 27, 2015 : “The deal has been causing astonishment for months - because the Ministry of Economic Affairs already has the data. The federal government financed three quarters of the "Terrasar-X / Tandem-X" project: 313 million came from tax revenues, 90 million from the project partner Airbus Defense & Space. "
  13. ^ GIM International: Weber, Marco; Koudogbo, Fifamè, January 2009, TerraSAR-X 1 m Spaceborne Radar- Use, Features, Products and TanDEM-X.