Tutorial HD-1: New SAR Missions and Concepts

Presented by: Manfred Zink and Gerhard Krieger
German Aerospace Center (DLR), Oberpfaffenhofen, Germany

Part 1 - The TerraSAR-X/TanDEM-X Missions:

After the successful participation in the Shuttle missions SIR-C/X-SAR and SRTM, the first national SAR mission TerraSAR-X opened a new era in the German Space Program. Launched in June 2007, TerraSAR-X is being operated in variety of imaging modes and providing high-quality radar data to the scientific community for a mission life time of at least five years. At the same time it is designed to satisfy the steadily growing demand of the private sector for remote sensing data in the commercial market. Early in the TerraSAR-X design phase, the proposal to add a second, almost identical spacecraft (TDX), to TerraSAR-X (TSX) and to fly the two satellites in a closely controlled tandem formation building a single-pass SAR-interferometer with adjustable baselines in across- and in along-track directions was born.

Three years after TSX, TDX was launched in June 2010 and since December 2010 the two satellites are orbiting at typical cross-track baselines of 150 - 400 m acquiring data for a global Digital Elevation Model (DEM) with 2 m relative height accuracy at a 12 m posting. Beyond that primary mission objective, TanDEM-X provides a configurable SAR interferometry test bed for demonstrating new SAR techniques and applications. TerraSAR-X and TanDEM-X are being implemented in a public-private partnership between the German Aerospace Centre (DLR) and EADS Astrium GmbH. This tutorial will present the mission concepts, give insight into details of the technical implementation and summarise the actual mission status and the results achieved.

Part 2 - New Missions and Concepts:

Synthetic Aperture Radar (SAR) is a well-established remote sensing technique that can provide high resolution radar images from space independent of weather and sunlight illumination. This makes SAR an ideal sensor for a continuous monitoring of the Earth surface and its intricate dynamics. The large scale mapping capabilities of current SAR systems are, however, rather limited and it takes typically several months until large contiguous regions can be acquired with high resolution. To overcome these limitations and to acquire novel geoinformation products, a new generation of SAR systems will be required.

This tutorial provides a comprehensive overview of new radar techniques and technologies that are well suited to boost the performance of future SAR missions by at least one order of magnitude. One key technology is digital beamforming which employs multiple antenna apertures in combination with individual receiving channels to overcome several inherent limitations of current SAR sensors. The information acquired by multiple apertures can be used to (1) suppress spatially ambiguous signal returns from the ground, (2) increase the receiving gain without a reduction of the imaged area, (3) suppress spatially localized interferences, and (4) gain additional information about the dynamic behaviour of the scatterers and their surroundings. The tutorial will introduce and discuss several digital beamforming techniques that have been suggested over the last years to increase both the instantaneous coverage area and the spatial resolution of future SAR systems. In this context, we will also review some advanced Multiple-Input Multiple-Output (MIMO) SAR modes and show how they may further improve the imaging capabilities.

Another opportunity to acquire novel information products arises from advanced bistatic and multistatic SAR systems. As a complement to TanDEM-X, various additional bi- and multistatic configurations will be introduced and their potential be assessed with regard to different remote sensing applications like frequent monitoring, silent operation, wide-swath SAR imaging, scene classification, single-pass cross-track and along-track interferometry as well as resolution enhancement. Essential steps in the system and mission design will be explained together with a discussion of major challenges such as phase and time synchronisation, bi- and multistatic SAR processing, safe formation flying as well as relative position sensing. The focus of the tutorial will be on new spaceborne SAR systems and missions, but some examples from airborne campaigns will also be provided for illustration.


Manfred Zink:

Manfred Zink received the Dipl.-Ing. degree in physics from the Technical University of Graz, Graz, Austria, in 1987, and the Dr.-Ing. degree from the University of Stuttgart, Stuttgart, Germany, in 1993. In 1988, he was with the Microwave and Radar Institute, German Aerospace Center (DLR). He has pioneered the calibration techniques for both air- and spaceborne SAR sensors and was responsible for building up the Oberpfaffenhofen calibration site. He was the Lead X-SAR Calibration Engineer for both SIR-C/X-SAR missions in 1994 and for the SRTM mission in 2000. In August 2000, he was with the European Space Agency (ESA) and took over the responsibility for the calibration/validation of the ASAR onboard the ENVISAT satellite. After successful in-orbit commissioning of the ASAR, he was appointed as the Principal System Engineer for Phase B of ESA's TerraSAR-L Program.

In 2005 Dr. Zink returned to the Microwaves and Radar Institute. Since the mission approval in 2006 he has been managing the TanDEM-X Ground Segment development. Building on almost twenty years of experience on SAR systems he became the driving force for the implementation of this unique mission and the solution of numerous challenging system engineering issues. At the European SAR (EUSAR) conference in 2008 he received the best paper award for his presentation of the TanDEM-X mission concept. Dr. Zink is currently heading the Satellite SAR Systems Department at the Microwaves and Radar Institute.

Gerhard Krieger:

Gerhard Krieger received the Dipl.-Ing. (M.S.) and Dr.-Ing. (Ph.D.) degrees (with honors) in electrical and communication engineering from the Technical University of Munich, Germany, in 1992 and 1999, respectively.

From 1992 to 1999, he was with the Ludwig-Maximilians University, Munich, where he conducted multidisciplinary research on neuronal modeling and nonlinear information processing in biological and technical vision systems. In 1999, he joined the Microwaves and Radar Institute (HR) of the German Aerospace Center (DLR), Oberpfaffenhofen, Germany, where he developed signal and image processing algorithms for a novel forward looking radar system employing digital beamforming on receive. From 2001 to 2007 he led the New SAR Missions Group which pioneered the development of advanced bistatic and multistatic radar systems as exemplified by the forthcoming TanDEM-X mission as well as innovative multi-channel SAR techniques and algorithms for high-resolution wide-swath SAR imaging. Since 2008, he has been Head of the Radar Concepts Department of the Microwaves and Radar Institute, DLR, Oberpfaffenhofen, Germany.

Dr. Krieger received several national and international awards, including the W.R.G. Baker Prize Paper Award from the IEEE board of directors and the IEEE Transactions Prize Paper Award of the Geoscience and Remote Sensing Society. He is author of more than 40 peer reviewed journal papers, 4 invited book chapters, about 250 conference papers, and 5 patents. His current research interests focus on the development of multi-channel radar techniques and algorithms for innovative MIMO SAR systems, the demonstration of novel interferometric and tomographic Earth observation applications, and the conceptual design of advanced bi- and multistatic radar missions.