WorldDEM™A New Dimension of Accuracy
The combination of accuracy, quality and coverage of WorldDEM™ constitutes a quantum leap in global digital elevation modelling. The unique accuracy of this dataset will surpass that of any global satellite-based elevation model available today. WorldDEM™ will thus replace the 10-year-old SRTM.
The following digital elevation models are derived from a first coverage acquired by TerraSAR-X and TanDEM-X in bi-static mode. The examples are therefore intermediate DEMs, which will be refined further with additional coverages. But this first coverage already provides a very promising glimpse of the quality of the final WorldDEM™ dataset, as in areas with “easy” terrain characteristics this first overflight delivered quality levels close to the final product specifications.
Following completion of the first coverage of the Earth’s entire landmass, the two satellites are continuing with the second full coverage, which will be completed in early 2013. To assure the consistently high quality and accuracy of the final dataset, selected more complex terrain areas will be covered with a third and fourth acquisition.
Adding a New Dimension of Accuracy
The above comparison of SRTM 90 (left) and WorldDEM™ (right) data of an area in Minnesota, USA, illustrates the substantial improvement in accuracy and quality of the new dataset. In the newly acquired data the terrain is depicted in much more detail and numerous features that were not distinguishable before are now clearly visible, such as buildings, roads and vegetation.
The WorldDEM™ will offer vertical accuracy of 2m (relative) / better than 10m (absolute) in a 12m x 12m raster. The dataset will afford overall homogeneity with no break lines at regional or national borders and no heterogeneities caused by varying measurement procedures or data collection campaigns staggered in time.
Revealing New Details
(Location: North Dakota, USA)
The image illustrates a comparison between two SAR acquisitions (left) and WorldDEM™ data (right). The representation of objects in SAR imagery can be affected by seasonal effects (such as soil moisture content or snow coverage), as these produce different radar backscatter characteristics. For this reason, a distinct difference can be observed in the SAR image mosaic: the left image was recorded in winter, when the ground was possibly covered by snow or ice, producing a different radar backscatter than in the right image that was most likely acquired in autumn. This difference is to a small extent also visible in the DEM, however, thanks to the multiple coverages processed into the final WorldDEM™ dataset, such seasonal effects will be eliminated.
Besides distinct terrain features such as elevation and river beds, more subtle features can be clearly distinguished, for example buildings and power pylons as well as elevated roads and highway interchanges.
A New Level of Quality
(Location: North Dakota, USA)
This image illustrates a comparison of WorldDEM™ data (right) with LiDAR-derived data (left). Even though LiDAR data evidently provide higher accuracy and clearly distinguishable terrain features, the spaceborne WorldDEM™ data surprise with an impressive level of detail, with houses, roads and vegetation in this urban area clearly discernable. The statistical comparison of height data between the two data sources as marked by the elevation measurement in the image additionally highlights the unique accuracy achieved by the TanDEM-X mission.