TECHNOLOGY FOR CHANGE

Twin Satellites to Produce Most Complete Hi-Res 3D Map of Earth's Surface

Salvatore Salamone | Date: 06-25-10 | Comments

A new German effort to produce a high-resolution 3D elevation map of the entire Earth�s surface is now underway.

A new German effort to produce a high-resolution 3D elevation map of the entire Earth�s surface is now underway. Once completed, this digital elevation model (DEM) of the Earth has many practical applications.

The effort to create the DEM will use twin radar imaging satellites, flying close together (within about a few hundred yards apart at times).

The first satellite, called the TerraSAR-X, was placed in orbit in 2007. The second satellite, called TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement), joined its twin this week on June 21.

Together, the satellites, which orbit at an altitude of about 320 miles (514 km), will constitute the first configurable synthetic aperture radar (SAR) interferometer in space. Using the SAR interferometry technique, an area on the Earth�s surface will be imaged from two different viewing positions, giving different perspectives. This is similar to the way humans use their two eyes to get an accurate, 3D image, according the researchers.

Flying in formation, TanDEM-X and TerraSAR-X will generate a precise global elevation model (Source: DLR).

The twin satellites will survey the entire land surface area of the Earth several times over. This process will be completed within three years. �This will be the first time we will ever have had a globally standardized 3D digital elevation model of Earth,� says Dr. Alberto Moreira, Science Director of the TanDEM-X mission and Director of the DLR Microwaves and Radar Institute.

The program is expected to produce a DEM with a vertical resolution of about six-and-a half feet (specifically, two meters) and a spatial resolution of about 40 feet by 40 feet (more precisely, 12 meters by 12 meters).

To put these numbers into perspective, the best previous large-scale Earth DEM effort was the U.S. Space Shuttle Radar Topography Mission (SRTM) conducted 10 years ago in 2000. According to the BBC, that effort yielded information with a vertical resolution that varied from about 32 feet to 52 feet instead of the six-and-a-half feet with this new project. The 2000 effort also had less granular surface spatial resolution.

The TanDEM-X group has created a graphic to depict the improvement that they expect with the improved resolution. As can be seen in the graphic below, the higher resolution offered by TanDEM-X yields much finer details about surface elements.

For vast swathes of Earth, at present only rough, inconsistent, or incomplete elevation models are available from different data sources and measurement techniques. TanDEM-X will close these gaps and will provide precise elevation data (Source: DLR).

Researchers point out that finer-resolution 3D mappings using other techniques exist. For example, airborne LIDAR measurements can be finer and more granular. However, such measurements have only been made over limited geographical regions.

Uses Aplenty for the Data

The German Aerospace Center (Deutsches Zentrum f�r Luft- und Raumfahrt, known as DLR) manages TanDEM-X and is responsible for mission operations and for generating the scientific data. The entire program is being run as a public-private partnership between the DLR Astrium GmbH, with DLR funding coming from the German Ministry of Economics and Technology. Infoterra GmbH, a subsidiary of Astrium, is responsible for the commercial marketing of the TanDEM-X data.

That data is expected to have uses in a wide range of applications. Cell phone system operators could use it to identify where to place transmission towers, commercial aviation groups could use the data to plan safer flights, city planners could use the data to assess flood risks in urban areas, and military fliers could use the information to fly missions closer to the ground.