WorldDEM: A Seamless Global Digital Elevation Model from TanDEM-X and TerraSAR-X

The launch of TanDEM-X on June 21, 2010 marked the beginning of a transformative phase in global elevation mapping. Working in tandem with TerraSAR-X, the satellite forms part of a precision radar interferometry mission designed to create a consistent, high-accuracy digital elevation model (DEM) for the entire terrestrial surface of the Earth.

Flying in a tightly controlled helix formation—sometimes separated by only a few hundred meters—the two satellites operate as a bi-static radar interferometer. This coordinated configuration enables simultaneous data acquisition, providing the foundation for what has become known as WorldDEM, a seamless global height model intended to replace legacy elevation datasets such as Shuttle Radar Topography Mission (SRTM).

A Global Elevation Model with Unprecedented Precision

The objective of the TanDEM-X mission is to generate WorldDEM with uniform quality from pole to pole. The resulting dataset is characterized by:

• Relative vertical accuracy of approximately 2 meters and absolute vertical accuracy of about 10 meters
• A spatial resolution of 12 meters by 12 meters
• Worldwide homogeneity
• Consistency achieved through a coordinated global acquisition window of roughly 2.5 years, with opportunities for additional targeted data collection
• Elimination of reliance on external ground control due to the exceptional geometric precision of the German radar instruments

Unlike optical systems, radar acquisition is independent of daylight and cloud cover, ensuring consistent data capture regardless of atmospheric conditions. The global campaign strategy eliminates discontinuities at political borders and avoids inconsistencies associated with regional measurement campaigns conducted at different times or with varying methodologies. The result is a continuous, standardized elevation framework suitable for global applications.

Mission Milestones and Operational Progress

Following its launch from Baikonur Cosmodrome in Kazakhstan, TanDEM-X delivered its first imagery within three days. Within a month—earlier than anticipated—scientists at German Aerospace Center processed initial digital elevation models derived from data captured by the TerraSAR-X/TanDEM-X formation, even before the satellites reached their final operational configuration.

On October 19, 2010, the mission achieved a landmark: the first DEM produced using a free-flying bi-static SAR satellite pair. The quality and accuracy of these early results validated the technical approach. Full operational status was declared on December 14, 2010.

By early 2012, the mission had completed its first comprehensive coverage of Earth’s landmass—an extraordinary accomplishment given the approximately 150 million square kilometers requiring seamless mapping. This achievement reflected the precision of the acquisition plan developed by DLR and Astrium engineers. Importantly, TerraSAR-X continued to fulfill its commercial and scientific obligations during this period, supporting time-series acquisitions, rapid response imaging and large-scale regional monitoring projects.

After the initial coverage, a second global acquisition campaign commenced, followed by targeted third-pass collections over complex terrain to ensure uniform data quality and accuracy across challenging landscapes.

Production, Refinement and Commercial Distribution

Infoterra GmbH, part of Astrium GEO-Information Services, holds exclusive commercial rights to WorldDEM. The company is responsible for tailoring the elevation model to meet civilian and defense requirements worldwide. Refinement processes include water surface editing and transformation into digital terrain models representing bare-earth conditions.

This refinement work is coordinated with the Bundeswehr Geoinformation Office (BGIO) and the National Geospatial-Intelligence Agency (NGA). Collaboration focuses on establishing standardized procedures for terrain editing and quality control.

To support these processes, specialized software tools are under development and tested using radargrammetric DEMs derived from multiple TerraSAR-X acquisitions. One derivative product, Elevation10, already demonstrates performance exceeding that of SRTM DTED Level 2. Additionally, DLR processes single-baseline interferometric data north of 60 degrees latitude to create reference datasets (IDEM), which can be offered commercially in an unedited Level-3 format.

International Collaboration: The WorldDEM Alliance

An initiative led by Infoterra/Astrium in cooperation with BGIO and NGA seeks to establish a multinational WorldDEM Alliance. The concept envisions participating nations sharing both editing responsibilities and associated costs. This collaborative framework aims to maintain consistent quality standards across all contributors while enabling flexible hosting and work-sharing arrangements for the final dataset.

Applications Across Civil and Defense Domains

High-precision elevation data underpin virtually all advanced geospatial products. WorldDEM’s uniformity and resolution enhance thematic mapping, terrain analysis, infrastructure planning and environmental monitoring. The dataset supports surface deformation studies, change detection analysis and urban expansion monitoring, since the radar data collected for DEM generation can also inform temporal assessments.

For both civil and military Earth observation operators, the availability of a standardized elevation reference simplifies orthorectification workflows anywhere on the globe. National mapping agencies can update topographic products with improved height accuracy, while planners benefit from a consistent foundation for cross-border operations.

The absence of seam lines or regional inconsistencies facilitates international cooperation and joint mission planning. In emergency scenarios—natural disasters, environmental crises or humanitarian operations—rapid access to a reliable and globally consistent DEM enhances situational awareness and enables more effective coordination on the ground.

WorldDEM represents more than a technical upgrade over SRTM. Through the combined capabilities of TanDEM-X and TerraSAR-X, Germany has delivered a globally uniform, high-accuracy digital elevation framework that supports the next generation of geospatial analysis, defense planning and Earth observation science.