Global Topography Measurements with TanDEM-X

TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurements) is an innovative formation flying radar mission that opens a new era in spaceborne remote sensing. The primary objective of TanDEM-X is the generation of a global digital elevation model (DEM) with unprecedented accuracy and resolution (12 m horizontal and 2 m vertical resolution). This goal is achieved by extending the TerraSAR-X synthetic aperture radar (SAR) mission by a second, TerraSAR-X like satellite (TDX) flying in close formation with TerraSAR-X (TSX). Both satellites form together a large singlepass SAR interferometer with the opportunity for flexible baseline selection. This enables the acquisition of highly accurate cross-track interferograms without the inherent accuracy limitations imposed by repeat-pass interferometry due to temporal decorrelation and atmospheric disturbances. Besides the primary mission goal several secondary objectives employing new bistatic SAR techniques have been defined, which represent an additional asset and innovation of the TanDEM-X mission. TanDEM-X is implemented in the framework of a public-private partnership between the German Aerospace Center (DLR) and EADS Astrium GmbH. The TanDEM-X mission was successfully launched in June 2010 and started operational data acquisition in December 2010. This paper provides an overview of the TanDEM-X mission and summarizes its actual status and performance. Special emphasis is put on the methodology used to retrieve the DEM and the main challenges encountered. Several examples show that the accuracy meets or even exceeds the expectations and a direct comparison with existing global DEMs reveals the leap in quality that is achieved by the TanDEM-X topography measurements. Furthermore, the results from several scientific experiments will be presented that show the great potential of future formation flying interferometric SAR missions to serve new applications