TerraSAR-X, is an imaging radarEarth observation satellite, a joint venture being carried out under a public-private-partnership between the German Aerospace Center (DLR) and EADS Astrium. The exclusive commercial exploitation rights are held by the geo-information service provider Astrium. TerraSAR-X was launched on 15 June 2007 and has been in operational service since January 2008. With its twin satellite TanDEM-X, launched 21 June 2010, TerraSAR-X acquires the data basis for the WorldDEM, the worldwide and homogeneous DEM available from 2014.
Using a phased arraysynthetic aperture radar (SAR) antenna (X-band wavelength 31mm, frequency 9.65 GHz[2]), TerraSAR-X provides radar images of the entire planet from an Earth polar orbit of 514km altitude. This is selected so that the satellite follows a Sun-synchronous orbit. This specific orbit means that the satellite moves along the Day-Night boundary of the Earth and allows it to present the same face to the Sun: thus, providing the best solar incidence angles to its solar cells for power. TerraSAR-X is designed to carry out its task for five years, independent of weather conditions and illumination, and provides radar images with a resolution of up to 1m.
TerraSAR-X acquires radar data in the following three main imaging modes:
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 16 m resolution, scene size 100 km (width) × 150 km (length);[3]
Wikimedia Commons has media related to TerraSAR-X.
In addition, the design of TerraSAR-X's SAR antenna allows a variety of polarimetric combinations: single or dual polarization, or full polarimetric data takes.
Depending on the desired application, one of four different processing levels is selected:
TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurements) is a second, similar spacecraft launched on 21 June 2010 from Baikonur Cosmodrome in Kazakhstan. Since October 2010, TerraSAR-X and TanDEM-X have orbited in close formation at distances of a few hundred metres and record data synchronously.[4]
This twin satellite constellation will allow the generation of WorldDEM, the global digital elevation models (DEMs). With higher accuracy, coverage and quality – WorldDEM is a consistent DEM of the Earth's land surface is envisaged to be acquired and generated within three years after launch. Available from 2014, WorldDEM is to feature a vertical accuracy of 2m (relative) and 10m (absolute), within a horizontal raster of approximately 12x12 square meters, slightly varying depending on the geographic latitude.[5]
Radar stands for Radio Detection and Ranging and contains traditionally:
Range finding (EDM) by means of the time a reflected signal needs to return;
Direction measurement over the adjustment of the antenna, and;
Different analysis such as SAR, polarization and Interferometry.
Satellite radar systems came into operation over fifteen years after the adoption of optical camera systems. The resolution is lower than optical imaging, but radar can gather information at any time of the day or night and independent of cloud cover.
Early radar satellite techniques were e.g. the Altimetrie (leveling over the sea), NASA's SEASAT (launched in 1978), regulation of waves/wind or soil data. The military has used radar since the late 1930s and radar satellites at least since 1978.[6]
TerraSAR X introduced some technical-industrial novelties. One of these innovations is a kind of zoom shot, with the resolution and scanning field vice versa changeable in a 1:10 relationship, either a larger area to grasp or a small area with the highest possible resolution.
Furthermore, the antenna can be aligned by electronics within an angle range so that the point of view is adjustable. Earlier radar satellites could radiate the antenna only in one direction.
With the adjustable angle radar sensor – along with other course refinements (precession by the earth flattening) – any place on earth can be observed preferentially within 1 to 3 days.
For a specific point on the Earth's equator, TerraSAR X has a revisit cycle of 11 days. The revisit time decreases towards the poles, e.g. Northern Europe has a revisit time of typically 3–4 days.
The ground operating mechanism and controls for the TerraSAR X is developed by the DLR in Oberpfaffenhofen.
It consists of Mission Operating Equipment, the Payloadground segment and the Instrument Operation and Calibration Segment. At the base of the ground segment lies the German Space Operation Center (GSOC), the German Remote Sensing Datum Center (DFD) as well as Institutes for Methodology of Remote Sensing (MF) and the Institute for High-Frequency Engineering and Radar Systems (HR) which are all part of the DLR.
Applications of the high-resolution TerraSAR-X radar imagery include:
Topographic Mapping: 2D and 3D, in scales down to 1:25,000, map updates
Surface Movement: Based on time series acquired by TerraSAR-X over the same area surface displacements caused by subsurface mining, oil-/gas extraction, infrastructure construction, excavations, or underground engineering can be visualised.[7]
Change Detection: for the monitoring of large-scale construction projects, infrastructure networks, monitoring and documentation of changes and developments
Land Cover and Land Use Mapping: accurate and up-to-date land cover / land use informations, also from places, where it is difficult to get informations with using other technologies because of permanent cloud cover
Defence and Security Applications: Applications include effective mission planning, the quick assessment of natural or manmade disasters or border control through detection of paths (changes), fences and moving objects
Rapid Emergency Response: due to its rapid revisit time TerraSAR-X is a reliable source of information in case of natural or man-made disasters (e.g. earthquakes, floods, military conflicts etc.) providing reliable information for disaster management and response allowing the recognition and assessment of damages to populated areas and traffic infrastructure, the identification of focus areas, and an efficient coordination of rescue actions.[8][9]
Environmental applications: e.g. forest monitoring, flood monitoring,[10] water quality applications
Further applications currently under evaluation: Traffic Monitoring, Maritime applications, vegetation monitoring
The scientific use of the TerraSAR-X data will be coordinated through the TerraSAR-X Science Service System by the DLR.[11] The new-quality data records, as provided by TerraSAR-X, will offer a vast amount of new research incentives, for instance in ecology, geology, hydrology and oceanography. The smallest movements of the Earth's surface (plate tectonics, volcanism, earthquake) are further scientific fields of application.
To ensure the commercial success of the mission, EADS Astrium founded its 100% subsidiary Infoterra in 2001; the company being responsible for establishing a commercial market for TerraSAR-X data as well as TerraSAR-X-based geo-information products and services.
The radar remote sensing satellites TanDEM X and Terra SAR X photographed while flying in close formation (photo by Marco Langbroek, Leiden, the Netherlands). Movement is from lower right to upper left in this 10-second exposure.
^GIM International: Weber, Marco; Koudogbo, Fifamè, January 2009, TerraSAR-X 1m Spaceborne Radar – Use, Features, Products and TanDEM-X.
^(Jensen, J. R. 2007. Remote Sensing of the Environment: An Earth Resource Perspective)
^GeoBerichte 14, Landesamt für Bergbau, Energie und Geologie in Niedersachsen:Schrage, Thomas;Jacob, Philipp, June 2009, Flächenverbrauch und Bodenversigelung in Niedersachsen.
^GIM International: Balz, Timo; Scheuchl, Bernd;Li, Deren, October 2008, The Sichuan Earthquake(1)-Satellite Imagery for Rapid Response.
^GIM International: Shao, Yun; Scheuchl, Bernd, November 2008, The Sichuan Earthquake (2)- Spaceborne SAR in Earthquake Response.
^GIM International: Koudogbo, Fifamè; Müller, Marc; Scheuchl, Bernd, December 2008, The Sichuan Earthquake (3)- Satellite-based Global Flood Response.
Launches are separated by dots ( • ), payloads by commas ( , ), multiple names for the same satellite by slashes ( / ). Crewed flights are underlined. Launch failures are marked with the † sign. Payloads deployed from other spacecraft are (enclosed in parentheses).
