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Abstract-TanDEM-X is an innovative single-pass radar interferometric mission, which is comprised of two formation flying satellites, with the primary goal of generating a global Digital Elevation Model (DEM) of unprecedented accuracy. Between December 2010 and early 2015 all land surfaces have been acquired at least twice, difficult terrain up to seven or eight times and as of September 2016 the final TanDEM-X DEM dataset is available for download. This paper provides a final quality assessment of the TanDEM-X global DEM products with respect to the DEM relative and absolute height accuracy and data coverage both at the global and geocell level.

ABSTRACT:TanDEM-X is an innovative synthetic aperture radar (SAR) mission with the main goal to generate a global and homogeneous digital elevation model (DEM) of the Earth's land masses. The final DEM product will reach a new dimension of detail with respect to resolution and quality. The absolute horizontal and vertical accuracy shall each be less than 10 m in a 90% confidence interval at a pixel spacing of 12 m. The relative vertical accuracy specification for the TanDEM-X mission foresees a 90% point-to-point error of 2 m (4 m) for areas with predominant terrain slopes smaller than 20% (greater than 20%) within a 1° longitude by 1° latitude cell. The global DEM is derived from interferometric SAR acquisitions performed by two radar satellites flying in close orbit formation. Interferometric performance parameters like the coherence between the two radar images have been monitored and evaluated throughout the mission. In a further step, over 500,000 single SAR scenes are interferometrically processed, calibrated, and mosaicked into a global DEM product which will be completely available in the second half of 2016. This paper presents an up-todate quality status of the single interferometric acquisitions as well as of 50% of the final DEM. The overall DEM quality of these first products promises accuracies well within the specification, especially in terms of absolute height accuracy.

TanDEM-X is a single-pass radar interferometric mission, which is comprised of two formation flying satellites, with the primary goal of generating a global Digital Elevation Model (DEM) of unprecedented accuracy. Between December 2010 and early 2015 all land surfaces have been acquired at least twice, difficult terrain up to seven or eight times and as of September 2016 the final TanDEM-X DEM dataset is available for download. This paper provides a final quality assessment of the TanDEM-X global DEM products with respect to the DEM relative and absolute height accuracy and data coverage both at the global and geocell level.

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The TanDEM-X mission, formed by the TanDEM-X satellite (TDX) in cooperation with its almost identical twin TerraSAR-X (TSX), has mainly been designed to acquire bistatic Synthetic Aperture Radar (SAR) images of the Earth. Initiated in 2010, the primary mission objectives were to generate a global Digital Elevation Model (DEM), to perform scientific measurements and to explore novel SAR techniques. Up to the present day all these objectives have been completed with outstanding results. In addition, the satellites maintained a stable image quality from the start throughout their entire lifetime. The ground segment, which was tailored to the capabilities of the space segment, as well as an excellent design and manufacturing of the satellites were the key elements to achieve such a performance. In addition, the elaborate calibration concept and a careful treatment of the on-board resources enabled full operability up to the present day and allowed additional mission objectives such as the generation of a Change-DEM layer as an update to the global DEM. The stable bus and SAR payload performance as revealed by long-term system monitoring provide the basis for further extension of the TanDEM-X mission for several more years. In the following paper these long-term system monitoring results are presented to provide an overview of the evolution of the radar system. The results and experience gained with more than a decade of TanDEM-X mission operation are a great value for both the scientific and commercial community and serve as a forerunner for the development of future SAR missions.

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