In the last 5 years, the Institute has actively participated and also initiated several SAR missions and research programs that are decisive for its long-term strategy. Important examples are TerraSAR-X, TanDEM-X, F-SAR (new airborne SAR) and SAR-Lupe.
It is also working on future remote sensing and reconnaissance systems, such as Sentinel-1 (Copernicus program of EU/ESA), TerraSAR-NG (follow-on to TerraSAR-X), HRWS (next generation X-band SAR with high-resolution wide-swath imaging), Tandem-L (L-band mission proposal) BIOMASS (ESA Earth Explorer mission), VABENE (DLR project for traffic monitoring with radar) and the SAR-Lupe follow-on program. These projects are accompanied by research programs that ensure the Institute keeps a step ahead in the development of new research fields. Examples of such research programs are bistatic and multistatic SAR systems, digital beamforming, inverse SAR, polarimetric SAR interferometry and tomography, calibration, signatures, propagation, antennas, as well as radiometry and imaging techniques for security.
On June 15, 2007, Germany's first operational radar satellite TerraSAR-X was launched into orbit. The mission is implemented in a public-private partnership (PPP) between DLR and EADS Astrium GmbH. The TerraSAR-X satellite has been developed by EADS Astrium GmbH; four DLR Institutes in Oberpfaffenhofen have developed the ground segment and are operating the mission.
|Within four months TerraSAR-X took multiple acquisitions over Mexico City. The combination of these images shows subsidences in parts of the city of up to10 cm due to removal of ground water.
TerraSAR-X supplies high-quality radar data for a mission life-time of at least five years (current expectation is more than six years). In this context, TerraSAR-X serves two main goals: 1) To provide the scientific community with multi-mode X-band SAR data, and 2) to establish a commercial Earth observation market, i.e. to develop a sustainable EO business, so that follow-on radar satellite systems can be completely financed by industry from the revenues.
TerraSAR-X is an advanced X-band radar satellite with a phased array antenna consisting of 384 transmit and receive modules. The antenna is fixed mounted to the spacecraft body and spans an overall aperture size of 4.8 x 0.7 m. The center frequency of the radar instrument is 9.65 GHz with a selectable system bandwidth of up to 300 MHz. Variable antenna beams and multiple operation modes can be selected like stripmap (3 m resolution, 30 km swath width), scanSAR (16 m, 100 km swath width), or high-resolution spotlight mode (1 m, 5/10 x 10 km image size). The imaging modes can be further combined with different polarization settings. In the scope of the calibration activities for TerraSAR-X, it has been demonstrated that the calibration accuracy of the radar images is better than 0.3 dB and that the geo-localization accuracy is in the order of 30 centimeters.
The Institute has contributed to the TerraSAR-X project with a dedicated SAR system engineering activity with the design, implementation and operation of the Instrument Operations and Calibration System (IOCS) and with the development and execution of the end-to- end system calibration. Beyond these tasks, the Institute also holds the position of the Mission Manager who chairs the Mission Board, also including the science and the commercial coordinators.
The Mission Board decides on the strategic planning and all issues related to daily business, nominal operations and contingencies. Representing the German federal government, the DLR is the sole owner of the TerraSAR-X data and coordinates the scientific data utilization.
TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement), initiated jointly by the Microwaves and Radar Institute and EADS Astrium GmbH in 2003, opens a new era in spaceborne radar remote sensing. A single-pass SAR interferometer with adjustable baselines in across and along-track directions is formed by adding a second, almost identical spacecraft to accompany TerraSAR-X in a closely controlled formation. With typical across-track baselines of 200 – 400 m, a global digital elevation model (DEM) with 2 m relative height accuracy at 12 m horizontal posting is being generated. DEMs are of fundamental importance for a broad range of scientific and environmental applications. For example, many geoscience areas, like hydrology, glaciology, forestry, geology, oceanography, and environmental monitoring require precise and up-to-date information about the Earth’s surface and its topography.
|Digital elevation model of the Atacama Desert in Chile, generated by TanDEM-X, 2010.
Beyond the primary mission objective, TanDEM-X provides a configurable SAR interferometry test bed for demonstrating new SAR techniques (multistatic SAR, polarimetric SAR interferometry, digital beamforming and super resolution) and associated applications.
An orbit configuration based on a helix geometry has been patented by the Institute and was selected for safe formation flying of the two satellites. In order to allow accurate phase information in the bistatic acquisition mode, the radar instruments feature a new technique for exchanging phase information via dedicated microwave links.
Combined data acquisition planning for both the TerraSAR-X mission with single localized requests as well as for the TanDEM-X mission with a global DEM mapping strategy is a major challenge under the constraints of limited space segment resources. For generating the global DEM roughly 350 TByte of raw data will be acquired using a network of ground receiving stations. Processing to DEM products requires advanced multi-baseline techniques and involves mosaicking and a sophisticated calibration scheme on a continental scale. The global DEM will be available by January 2014. Besides the tasks in the development of the ground segment, the Institute is managing the ground segment project in Oberpfaffenhofen and coordinates the scientific activities of the TanDEM-X mission.
TanDEM-X represents an important step towards a constellation of bistatic and multistatic radar satellites and will provide sustained support for Germany’s leading role in spaceborne SAR technologies and missions.
Tandem-L is a mission proposal initiated by the Institute for an innovative interferometric L-band radar instrument that enables the systematic monitoring of dynamic Earth processes using advanced techniques and technologies. The mission is science driven, aiming to provide a unique data set for climate and environmental research, geodynamics, hydrology and oceanography. Important application examples are global forest height and biomass inventories, measurements of Earth deformation due to tectonic processes and/or anthropogenic factors, observations of ice/glacier velocity fields and 3-D structure changes, and the monitoring of soil moisture and ocean surface currents.
|Tandem-L: Simulation of the forest height derived from two radar acquisitions using polarimetric SAR interferometry. The forest biomass can be estimated from the forest height using an allometric equation and the forest profile. This image shows the area of Traunstein, Germany.
The Tandem-L mission concept consists of two cooperating satellites flying in close formation. The Pol-InSAR and repeat-pass acquisition modes provide a unique data source to observe, analyze and quantify a wide range of mutually interacting processes in the biosphere, lithosphere, hydrosphere and cryosphere. The systematic observation of these processes benefits from the high data acquisition capacity and the novel high-resolution wide-swath SAR imaging modes that combine digital beamforming with a large reflector antenna.
One key technology of Tandem-L is the use of a large reflector antenna in combination with digital beamforming in the feed array that illuminates the reflector. While all feed elements are used during transmission, allowing the illumination of a large image swath, 2-3 feed elements are activated during the receive window. The feed element positions are periodically shifted following the systematic variation of the direction of arrival of the swath echoes.
The advantages of this concept are manifold. First, the use of a large reflector antenna in connection with digital beamforming allows the reduction of the transmit power by a factor of 3-4 compared to the traditional SAR concept for the same imaging parameters. Second, it allows the mapping of a much wider swath (approx. 350 km) in high-resolution stripmap mode. The fully polarimetric acquisition in stripmap mode with a wide swath is possible without the constraints of conventional SAR systems.
It is planned to realize the Tandem-L mission in cooperation with an international partner. The mission concept was developed in detail in a two-year pre-phase A study and it will be further investigated in the next 18 months. The cooperation with an international partner will allow a cost-effective implementation, whereby each partner contributes with its predevelopments and experience. According to current planning, the Tandem-L satellites could be launched in 2019.
Future Research Activities & Projects
Looking ahead to the next years, the Institute will continue to initiate and contribute to several projects that will be decisive for its long-term strategy. The table below shows the most important projects in the Institute.
|Most important projects in the Institute. Bars in orange show the planned continuation of the respective project. Satellite launches are indicated by triangles.
The number of projects since 2006 has increased considerably. By means of the Institute’s contributions to the TerraSAR-X, TanDEM-X and SAR-Lupe projects, a highly qualified project team has been established. Due to the high degree of innovation in science and technology, the mission Tandem-L represents the most important project for the Institute in the years to come and can be seen as a next milestone in the national radar roadmap after TanDEM-X.
National Missions und Projects
TerraSAR-X and TanDEM-X are national high-resolution radar satellites launched in 2007 and 2010. The tandem operation of both satellites for DEM generation is planned until autumn 2016, but an extension of the operation is expected, because TerraSAR-X is still fully functional and has sufficient resources available. Although the nominal lifetime of TerraSAR-X is specified to be 5.5 years, an extension to more than 8 years is expected.
Tandem-L is a radar mission proposal in L-band. A pre-phase A study has been performed from 2008 to 2011. The study has been extended until 2014 in order to investigate a joint realization of Tandem-L with JAXA. The decision for implementation depends on an approval of the required funding which is expected to occur by the end of 2017.
The project RSE is fully funded by the German MoD and encompasses all activities of the Institute related to security and reconnaissance. It includes the technical support, engineering and mission analysis of SAR-Lupe and its follow-on system, as well as the passive microwave sensor developments.
Since 2009 the Institute has contributed to the TerraSAR-X2 phase A study. It is expected that TerraSAR-X2 will include new technological parts of a high-resolution wide-swath (HRWS) SAR system. Different to TanDEM-X, the requirements for TerraSAR-X2 are mainly driven by commercial applications. However, according to the PPP agreement, TerraSAR-X2 will ensure X-band data continuity for the scientific community.
Sentinel-1A and Sentinel-1B are two C-band radar satellites from the EU/ESA Copernicus program. Sentinel 1A was launched in April 2014. The launch of the twin satellite Sentinel 1B is planned for 2016. The Institute’s contribution lies in the definition of the end-to-end system calibration concept and algorithms. The Institute has already contributed in the calibration during the commissioning phase of the Sentinel-1 satellites and will also contribute to the calibration of the successor satellites of ESA.
BIOMASS (P-band SAR, fully polarimetric) is an Earth Explorer mission recommended for implementation. The Institute is involved in the calibration and several science studies for the two radar missions. For BIOMASS, the Institute is the prime contractor for the development of the complete end-to-end mission performance simulator. Further activities include flight campaigns with the airborne SAR.
The Institute also contributes to the Spanish PAZ satellite with the delivery of the SAR related software modules for instrument operations and calibration. The PAZ satellite is a TerraSAR-X based satellite, the launch is scheduled for 2015.
DLR Internal Projects
F-SAR is the new airborne SAR system of DLR that became fully operational by 2012. It is planned to expand the F-SAR system to include a digital beamforming capability by 2015. Several internal and external flight campaigns have already been executed with F-SAR since 2008, the intensive operational phase started in 2012.
F-SAR has been extended to a 4-channel system for road traffic monitoring (DLR internal project VABENE). The Institute has submitted a proposal for developing a low-cost, compact airborne SAR for road traffic monitoring based on the F-SAR technology. This project has started mid-2012.
The DLR projects MEPHISTO and ITEM-FK deal with UCAVs (Unmanned Combat Aerial Vehicles) and agile missiles, respectively. Several disciplines, like aerodynamics, flight control, material sciences, actuation, radar and infrared signatures are represented. The Institute's contributions are investigations concerning radar signatures, radar detection probabilities and radome microwave transmission.
The above mentioned projects are accompanied by several research programs.
Resource allocation in the Institute for the projects and research programs. More than 50% of the Institute’s resources are allocated to DLR projects and external contracts.
The table on the top summarizes the internal and external projects as well as the research programs that are funded by the DLR program directorates in the areas of space, aeronautics and transportation. Examples of research programs are new SAR concepts, signal processing, airborne SAR, information retrieval, calibration, and signatures. The research programs are closely interconnected with the project activities.
As a matter of fact, most of the current projects of the Institute have started as research programs with typical durations of 2 to 5 years. Due to the long-term aspect of the Institute’s projects, it has developed a roadmap for the future radar activities jointly with its partners in industry and research. This roadmap is being updated on a regular basis. As of today, the Institute has more than 70% of its resources allocated to DLR projects and external contracts. Considering the success in the approval of the new mid-term and long-term projects, it is expected that this percentage will be maintained above 70% in the next 5 years.