Johannes Böer

TanDEM-X: DEM acquisition in the third year era

TerraSAR-X add-on for digital elevation measurement (TanDEM-X) is a space-borne X-band SAR mission designed to derive a digital elevation model (DEM) of the Earth’s land surface with an unprecedented relative vertical accuracy of 2 m at a 12 m posting. To achieve this goal, the two satellites fly in close controlled formation with the opportunity to adjust flexible along- and across-track baselines. A combination of multiple acquisitions with different baseline lengths is required to allow stable phase unwrapping and to achieve the high height accuracy. This paper provides an overview of the TanDEM-X acquisition plan for the third year over Antarctica, mountainous areas and deserts. Critical aspects of the areas to be acquired are presented and the acquisition strategy is illustrated. Moreover, the formation flight and the baselines are compared to the ones of the previous years in terms of their impact on the height of ambiguity and on the performance with respect to the interferometric quality.

TerraSAR-X Instrument Operations Rooted in the System Engineering and Calibration Project

This paper presents the TerraSAR-X instrument operations embedded into the Instrument Operations and Calibration Segment. Special focus is on the data-take (DT) command generation. The command generation for standard DTs is discussed, and the nonnominal DT commanding is described for several examples which demonstrate the flexibility of both the TerraSAR-X instrument and the instrument operations system on-ground.

Determening the optimum compromise between SAR data compression and radiometric performance -An approach based on the analysis of TerraSAR -X data-

Data compression is crucial for modern synthetic aperture radar systems where high resolution or large coverage may result in huge amounts of raw data. Modern satellite systems, such as TerraSAR-X, give complete flexibility in choosing between various compression levels. This, however, results in additional effort to decide on the suitable compression level used, which may depend on the operation mode, polarization, scene backscatter, etc. The paper describes the approach used in the case of TerraSAR-X and shows the result of analyzing the data acquired during the commissioning phase. The methology is considered novel in the sense that it combines SAR measured data analysis with theoretical, i.e. model based simulations, results and later combines theory and measured data to extract optimum compression levels.

TerraSAR-X Instrument, SAR System Performance & Command Generation

The paper presents selected results from the TerraSAR-X Commissioning Phase from instrument performance, SAR system performance and command generation.

TanDEM-X acquisition status and calibration of the interferometric system

TanDEM-X is a spaceborne SAR mission with the goal to derive a global Digital Elevation Model (DEM) with unprecedented accuracy. This paper describes the way how the global DEM is acquired, explains the changes that have been applied during the first almost 1.5 years in orbit and shows the actual status of the global acquisitions. In the second part, the calibration of the bi-static interferometer is explained. The implications to correct the different effects coming from the baseline, the internal delays in the instrument and the phase measurements themselves enabling the derivation of the height are described and the actual results are presented.

THE TanDEM-X Mission: Overview and status

TanDEM-X opens a new era in space borne radar remote sensing. The first bistatic SAR mission, is formed by adding a second, almost identical spacecraft, to TerraSAR-X and flying the two satellites in a closely controlled formation with typical distances between 250 and 500 m. Primary mission objective is the generation of a consistent global digital elevation model with an unprecedented accuracy according to the HRTI-3 specifications. Beyond that, TanDEM-X provides a highly reconfigurable platform for the demonstration of new SAR techniques and applications. This paper gives an overview of the TanDEM-X mission concept, summarizes the capabilities of the system, illustrates the achievable performance, and provides some examples for new imaging modes and applications. The mission has been approved for full implementation by the German Space Agency with a planned launch in spring 2009.

TanDEM-X going for the DEM: Acquisition, performance, and further activities

TanDEM-X is an innovative spaceborne X-band SAR mission designed to derive a digital elevation model (DEM) of the Earths land surface with an unprecedented relative vertical accuracy of 2m at a 12m posting. The global DEM is derived from interferometric SAR acquisitions performed by two radar satellites flying in close orbit formation, with adjustable baselines in cross- and in along-track directions. This paper provides an overview of the present mission status in terms of acquisition strategy and a quality summary of the currently available parts of the TanDEM-X global DEM in terms of absolute and relative height accuracy.

Ten Years of TerraSAR-X Operations

The satellite of the TerraSAR-X mission, called TSX, was launched on 15 June 2007 and its identically constructed twin satellite TDX, which is required by the mission TanDEM-X, launched on 21 June 2010. Together they supply high-quality radar data in order to serve two mission goals: Scientific observation of Earth and the provisioning of remote sensing data for the commercial market (TerraSAR-X mission) and the generation of a global digital elevation model (DEM) of Earth’s surface (TanDEM-X mission). On the occasion of the 10th anniversary of the mission, the focus will be on the development of the TerraSAR-X system during this period, including the extension of the ground segment, the evolution of the product portfolio, dedicated mission campaigns, radar experiments, refinement of the satellite operations and orbit control, and the results of the performance monitoring. Despite numerous interventions in the overall system, we managed to incorporate new scientific and commercial requirements and to improve and enhance the overall system in order to fulfill the increasing demand for Earth observation data without noticeable interruptions to ongoing operations.