The project to "map the Earth in 3D" is now entering its final preparation stage as the German Earth observation satellite TanDEM-X is readied for launch at the Baikonur Cosmodrome in Kazakhstan. On 21 June, at approximately 04:14:02 CEST, the satellite is due to be launched in to orbit at an altitude of 514 kilometres using a Dnepr launch vehicle.

Having moved into the combined operations phase, the launch service provider Kosmotras has assumed responsibility for the satellite hardware from Europe's leading space company Astrium. TanDEM-X is now being integrated into the space head module.

Surveying the Earth in formation flight
The TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement) mission demonstrates once again the world-beating German expertise in satellite-based radar technology: the primary mission objective is to record all the Earth's landmasses in 3D, or to be more precise, create a global digital elevation model with unprecedented accuracy.

The latest-generation Earth observation satellite will considerably extend scientific and commercial applications in this field.

Located just a few hundred metres apart, the two German satellites TanDEM-X and the virtually identical TerraSAR-X, which was launched in 2007, will form the first SAR interferometer in space. TanDEM-X is designed for a service life of at least five years and has a planned, overlapping deployment time with TerraSAR-X of at least three years.

Over this period, the satellite duo will survey the Earth's entire land surface - 150 million square kilometres - in formation flight. Elevation information with an absolute precision of better than two metres is achieved for a 12 metre grid.

The specific advantage of satellite-based remote sensing over an aircraft-based solution is that it provides a global, homogeneous terrain model without any discontinuities at country borders or inconsistencies that might arise from different measurement techniques. The use of radar plays a decisive role in this respect since it can be operated independently of weather and lighting conditions.

A wide range of applications
Digital elevation models are fundamental for a wide range of applications: geoscientific disciplines such as hydrology, geology and oceanography call for precise up-to-date information about the properties of the Earth's surface.

Applications range from more efficient mining of the Earth's natural resources to optimised crisis deployment planning in disaster areas and for security missions. Digital maps are also a prerequisite for reliable navigation: their accuracy needs to keep pace with the increasing demands placed on global positioning.

The digital terrain model of the Earth will provide Germany with a unique data product in the near future, which can be used in initiatives and programmes such as ZKI (Centre for Satellite Based Crisis Information of the German Aerospace Centre (DLR)), GMES (Global Monitoring for Environment and Security) and GEOSS (Global Earth Observation System of Systems), as well as in security-related co-operation agreements.

Last but not least, commercial customers around the globe are already impatiently awaiting the TanDEM-X elevation model. As soon as the global TanDEM-X elevation model is available in 2013, remote sensing and geoinformation experts from the private sector, government agencies and defence/security establishments will be able to benefit from it in their day-to-day work.

Data processing at DLR in Oberpfaffenhofen - enrichment by Infoterra
A network of three TanDEM-X ground stations (Kiruna/Sweden, Inuvik/Canada and O'Higgins/Antarctica) is required to handle the immense quantities of raw data being transferred.

The data pass through three main processing stages. First the data segments transmitted by TanDEM-X to the receiver stations are checked, then the results are evaluated in the processing centre of the German Remote Sensing Data Centre (DFD) run by DLR in Oberpfaffenhofen, and the image data are processed into raw elevation models.

In a final step, the Mosaicing and Calibration Processor (MCP) generates the global digital elevation model from the raw elevation models. The related absolute orientation is corrected continent by continent by comparing blocks. The global elevation model dataset will run to 15 terabytes and be available some four years after the launch.

Infoterra GmbH will be solely responsible for customising the elevation model to the needs of commercial users as well as the related global marketing. As part of the data enrichment, Infoterra will process the raw data supplied by the satellite system in accordance with particular customer requirements.

This normally involves removing any remaining spikes (peaks or outliers caused by noise) and offsets (can occur due to radar shadow particularly in mountainous terrain) in the data, and editing the representation of expanses of water (ensuring a uniform water level and the right gradient of river courses).