TerraSAR-X

Radar image

With its phased array synthetic aperture radar (SAR) antenna (X-band wavelength 31 mm, frequency 9.6 GHz), TerraSAR-X acquires new high-quality radar images of the entire planet whilst circling Earth in a polar orbit at 514 km altitude. The orbit is selected such that the satellite flies in a sun-synchronous dusk-dawn orbit, which means that it moves along the day-night boundary of the Earth and always presents the same face to the sun, ensuring an optimum energy supply via the solar cells. TerraSAR-X is designed to carry out its task for five years, independent of weather conditions and illumination, and reliably provides radar images with a resolution of up to 1m.

Features of TerraSAR-X:

• resolution of up to 1 m,
• excellent radiometric accuracy,
• geometric accuracy unrivalled by any other commercial spaceborne sensor,
• quick site access time of 2.5 days max. (2 days at 95% probability) to any point on Earth,
• unique agility (rapid switches between imaging modes and polarisations)

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);[2]

Wikimedia Commons has media related to TerraSAR-X.

In addition, the unique design of TerraSAR-X's SAR antenna allows a variety of polarimetric combinations: single or dual polarization and even full polarimetric data takes, 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)

TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurements) is a second, very similar spacecraft launched successfully on 21 June 2010 from Baikonur Cosmodrome in Kazakhstan. Since October 2010, TerraSAR-X and TanDEM-X fly in a close formation at distances of only a few hundred metres and record data synchronously.[3] This unique twin satellite constellation will allow the generation of WorldDEM, the global digital elevation models (DEMs). With an unprecedented 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.[4]

Radar stood originally 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 recently;
• also different analysis such as SAR, polarization, Interferometry etc.

Satellite radar entered use more than fifteen years after optical camera systems did. The resolution (detail sharpness) is in principle lower, but radar can gather information at any time of the day or night and independent of cloud cover. This contributes significantly to the reliability of the system, a much-desired property.

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.[5]

TerraSAR X will exhibit 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 1–3 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 Payload Ground 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 timeseries 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.[6]
• 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. earth quakes, 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.[7][8]
• Environmental applications: e.g. forest monitoring, flood monitoring,[9] 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.[10] 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.

In order 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.

• OPS 3762: The very first SAR radar in space, 1964
• Seasat: The SAR radar in space in 1978
• SAR Lupe: Germany's military radar satellites
• SAR technology(Synthetic Aperture Radar)
• Earth observation technology
• Earth observation satellite
• Digital elevation model

Radars on the Space Shuttle:

• SIR-A (Shuttle Imaging Radar) aboard STS-2 in 1981
• SIR-B aboard STS-41-G in 1984
• SRL-1 (Shuttle Radar Laboratory): SIR-C (Spaceborne Imaging Radar) and X-SAR (X-Band Synthetic Aperture Radar) on STS-59 in 1994
• SRL-2: SIR-C/X-SAR on STS-68 in 1994
• SRTM (Shuttle Radar Topography Mission) on STS-99 in 2000

(the TerraSAR-X authors were involved in SRL and SRTM missions)

Wikimedia Commons has media related to TerraSAR-X.

• Astrium Geo
• TerraSAR-X at DLR website.
• TerraSAR-X for risk management.
• TanDEM-X at DLR website.
• TanDEM-X Science Home at DLR website
• Terrasar-x at Astrium website