Elsevier

Acta Astronautica

Volume 89, August–September 2013, Pages 83-98
Acta Astronautica

TanDEM-X: A radar interferometer with two formation-flying satellites

https://doi.org/10.1016/j.actaastro.2013.03.008Get rights and content

Highlights

  • TanDEM-X is the first formation-flying radar interferometer in space.

  • TanDEM-X was successfully launched in June 2010 and is fully operational since December 2010.

  • Primary objective is the acquisition of a global digital elevation model with unprecedented accuracy.

  • Unique bistatic radar experiments demonstrate the potential for novel remote sensing products.

Abstract

TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurements) is an innovative formation-flying radar mission that opens a new era in spaceborne radar remote sensing. The primary objective is the acquisition of a global digital elevation model (DEM) with unprecedented accuracy (12 m horizontal resolution and 2 m relative height accuracy). 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 single-pass 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 goal of the mission, several secondary mission objectives based on along-track interferometry as well as new bistatic and multistatic SAR techniques have been defined, representing an important and innovative asset 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 satellite was successfully launched in June 2010 and the mission started its operational data acquisition in December 2010. This paper provides an overview of the TanDEM-X mission and summarizes its actual status and performance. Furthermore, results from several scientific radar experiments are presented that show the great potential of future formation-flying interferometric SAR missions to serve novel remote sensing applications.

Introduction

The primary objective of the TanDEM-X mission is the generation of a world-wide, consistent, timely, and high-precision digital elevation model (DEM) as the basis for a wide range of scientific research, as well as for commercial DEM production ([1], cf. Fig. 1). This goal is achieved by enhancing the TerraSAR-X synthetic aperture radar (SAR) mission [2] by a second radar satellite flying in close formation with TerraSAR-X [3]. Both satellites act together as a large single-pass SAR interferometer with the opportunity for flexible baseline selection. This enables the acquisition of highly accurate cross-track and along-track interferograms without the inherent accuracy limitations imposed by repeat-pass interferometry due to temporal decorrelation and atmospheric disturbances. Thanks to its unique capabilities, TanDEM-X is not only acquiring a global DEM with unprecedented accuracy, but it is also well suited to demonstrate novel bistatic and multistatic SAR techniques and Earth observation applications that form the basis for future formation-flying SAR missions. TanDEM-X has been implemented in the framework of a public–private partnership between the German Aerospace Center (DLR) and EADS Astrium GmbH, as for TerraSAR-X.

Section snippets

Mission concept

The TanDEM-X mission is an extension of the TerraSAR-X radar mission, co-flying a second satellite of nearly identical capability in a close formation. The TerraSAR-X satellite (TSX), as basis for TanDEM-X, was successfully launched into a sun-synchronous dusk-dawn orbit with 97.44° inclination on June 15, 2007. The nominal orbit height is 514.8 km and the orbit repeat cycle is 11 days. TSX is not only a high performance SAR system, but it has already built in all necessary features required for

Status summary

TanDEM-X was successfully launched into orbit on June 21, 2010. The initial separation between TDX and TSX was 15,700 km and after 1 month of drifting a formation in pursuit monostatic configuration with an along-track distance of 20 km was reached [17]. This formation was maintained for 3 months to calibrate the TanDEM-X radar instruments and to perform first bistatic and interferometric experiments employing large baselines (cf. Section 4). On October 14, both satellites were maneuvered into a

TanDEM-X experiments

TanDEM-X provides the remote sensing scientific community not only with a global DEM of unprecedented accuracy, but also with a unique reconfigurable SAR system to demonstrate novel bistatic and multistatic radar techniques for enhanced bio- and geophysical parameter retrieval. The following subsections summarize some of the advanced capabilities of TanDEM-X which can be operated in a multitude of modes and configurations [3]. Most of the provided results were already obtained during the

Conclusions

The TanDEM-X mission opens a new era in spaceborne radar remote sensing. A large single-pass SAR interferometer with adjustable baselines has been formed by adding a second, almost identical radar satellite to TerraSAR-X and flying both satellites in a closely controlled formation. This enables not only the acquisition of a global DEM with unprecedented accuracy, but also the demonstration of highly innovative bistatic and multistatic SAR techniques and applications. These experiments form the

Acknowledgment

We highly acknowledge the great effort and enthusiasm of all our colleagues at DLR and EADS Astrium who made this ambitious mission a reality. TanDEM-X is partly funded by the German Federal Ministry for Economics and Technology (50 EE 1035) and realized in a public–private partnership between German Aerospace Center (DLR) and Astrium GmbH.

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    This paper was presented during the 63rd IAC in Naples.

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