Cooperative aperture synthesis for tomographic radar imaging

The Research Training Group "Kooperative Apertursynthese für Radar-Tomographie“ (KoRaTo, engl: Cooperative aperture synthesis for tomographic radar imaging) is a joint project between the Ulm University (UUlm) and the Friedrich-Alexander-University (FAU) Erlangen-Nuremberg under the direction of Prof. Christian Waldschmidt, Institute of Microwave Engineering, Ulm University.

It aims at developing a new UAV- and radar-based geophysical monitoring system to measure for instance earth mass movements, vegetation heights, or the cryosphere. While in the past geophysical monitoring systems required ground vehicles, aircrafts, or satellites, KoRaTo breaks new grounds in using cooperative UAV swarms to synthesize a common high-resolution 3D-tomographic image of the environment. Through this, observations and explorations of so far rough or inaccessible terrain becomes possible and allows to look through ice layers or into hidden structures beneath the ground surface. This allows, for instance, to explore the stability of hillsides in order to monitor the avalanche danger. High resolution radar imaging is achieved by using small sub-radars carried by the UAVs that move in a swarm and together form a distributed sensor network that allows to carry out cooperative 3D measurements.

The challenges of the project encompass the synthesis of the cooperative measurements into a common 3D image, coordination and trajectory optimization of the swarm to achieve a common multistatic aperture, or the efficient storage and processing of the huge amounts of data. To achieve this goal, the KoRaTo project brings together researchers with different expertises such as microwave, remote sensing, and communication engineering.

The research priorities are

  1. Methods to spatially and temporally couple the non-coherent sub-radar apertures on different UAVs so that coherent, multistatic radar measurements for tomography and interferometry can be carried out;
  2. Optimized time-variant apertures, which are spanned by the movement of several UAVs, as well as jointly optimized trajectories of the movements;
  3. Methods for tomographic imaging in non-homogeneous media, made possible by the cooperative spatial aperture synthesis;
  4. Concepts for data storage, transmission and processing based on compressed sensing methods and resource optimization for the sensor data of the cooperative aperture synthesis.

The project is funded by the German Reseach Foundation (DFG) and further aims to train and promote young scientists in their individual research field.

Are you interested in joining us?

The KoRaTo-Team is looking for young researchers with outstanding degrees in Electrical Engineering specializing in microwave engineering, communications engineering, signal processing or with a similar background. We offer a stimulating, interdisciplinary research environment within an enthusiastic team at two internationally-oriented, open-minded and highly ranked universities. The doctoral studies will be embedded in a structured, interdisciplinary program with other young researchers of other disciplines. The UUlm and FAU are family-friendly employers and intend to increase the number of women in research and teaching positions and, therefore, strongly encourage female researchers to apply. In their pursuit of academic excellence, the UUlm and FAU are committed to equality of opportunity and to a proactive and inclusive approach, which supports and encourages all under-represented groups, promotes an inclusive culture, and values diversity.

Requirements are a Master's degree or comparable from a first-class university with a grade well above average, profound knowledge in one of the research areas listed below, and excellent knowledge of written and oral English (C1 and above). You should have the ability for cooperation and research in an interdisciplinary team, excellent social skills, and high motivation and commitment.

Go to job postings

Prof. Dr.-Ing. Christian Waldschmidt Project Manager Room: 41.2.303 Phone: 0731 50-26356 E-Mail

Research areas:

Wireless localization and synchronization techniques (FAU, Prof. M. Vossiek)

In this sub-project wireless localization and synchronization techniques will be investigated.  This synchronization and ultra-precise 6D localization is used to enable a coherent and joint measurement of several separated radar sensors that are carried by independent, mobile robots (UAV). Radio location technology for determining the constellation of robot swarms is an advanced and highly topical research area with a wide range of future applications. The candidates work at the interface between microwave transceiver and RFSoC based digital baseband design as well as on the development and implementation of advanced high speed signal processing algorithms. Therefore, they should have excellent knowledge in one or more of these areas.

The Institute of Microwaves and Photonics of FAU in Erlangen is one of the world's leading institutes in the field of wireless localization and radar technology and thus is enabling excellent career opportunities for doctoral students.

Multistatic radar networks for imaging (UUlm, Prof. C. Waldschmidt)

This sub-project deals with the question of how the radar sensors on drones can be coherently networked with one another, in order to achieve phase coherency. To this end, known approaches are to be expanded and new approaches fundamentally researched. The topic is a key aspect for future radar networks and is furthermore a very important and much debated topic in the international scientific discussion, to which KoRaTo should make a significant contribution. The candidates work at the interface between hardware design and signal processing concepts and should have excellent basic knowledge in both areas.

The Institute for Microwave Engineering at Ulm University is one of the world's leading research institutes in the field of radar technology and brings a lot of experience and background knowledge to KoRaTo. The doctoral students work in a strongly networked environment and can work well in a team thanks to a large number of similar research projects and can exchange their experiences with one another.

Resource management for UAVs and radar networks (FAU, Prof. R. Schober)

In this sub-project, novel resource allocation concepts for drone-based radar and communication systems are to be investigated. The resources available for data acquisition (sensing), communication, and the operation of the UAVs in such systems are severely limited due to the band limitation of the communication channel and the autonomous power supply of the UAVs. Therefore, the optimal allocation of the available resources is of great importance for the quality and quantity of the radar measurements. Applicants for this position are expected to have a strong background in optimization, machine learning, and wireless communications.

The Institute for Digital Communication at the Friedrich-Alexander-University Erlangen-Nuremberg conducts world-leading research in the general area of wireless communication and enjoys an excellent reputation internationally. It promotes a friendly, diverse, and collaborative work environment.

Tomographic imaging and geophysical parameter retrieval (FAU, Prof. G. Krieger)

This sub-project analyzes the potentials and challenges of interferometric and tomographic radar imaging with drone swarms and experimentally demonstrates novel geoscience applications. Each of the innovative applications requires a detailed observation planning in conjunction with a dedicated processing of the multistatic radar data. Special challenges to be resolved are the compensation of phase and motion errors and the development and implementation of a multidimensional signal processing chain up to the retrieval of geophysical parameters like digital elevation models and/or vertical structure profiles. The work will build up on the broad experience gained at the German Aerospace Center (DLR) with the processing of air- and spaceborne SAR data as well as the design, operation and calibration of innovative SAR missions like TanDEM-X.

The Institute of Microwaves and Photonics of FAU Erlangen is one of the world's leading research institutes in the field of radar technology and brings a lot of experience and background knowledge to KoRaTo. In addition to working closely with colleagues from the Institute and the Research Training Group, the PhD student will also collaborate with experts of DLR’s Microwaves and Radar Institute, which looks back to more than 40 years experience in radar remote sensing.

Distributed compressed sensing for radar networks (UUlm, Prof. R. Fischer)

In this sub-project the interaction between data acquisition in the radar sensors and the communication between the drones is studied. To this end, distributed compressed sensing is assessed for the specific situation and new approaches for data reconstruction which are tightly tied to the distributed nature of the sensing will be researched. Joint sensing and communications is currently one of the key research questions in the scientific community. The doctoral student will strongly interact with the radar and the resource optimization sub-projects and should have a strong background in communications and signal processing.

The candidate will built their work on the broad prior knowledge and expertise on compressed sensing and multi-antenna transmission available at the Institute of Communications Engineering. The doctoral students work in a strongly networked environment within KoRaTo and with complementing research project.

Wave propagation in inhomogeneous media (UUlm, Prof. C. Damm)

This sub-project deals with the material characterization of different sample materials relevant to the KoRaTo project, such as soils, ice, snow, or vegetation, and the modeling of wave propagation within these materials considering inhomogeneous material distributions. Practical measurements as well as theoretical analysis and modeling are equally required. In close cooperation with other projects within KoRaTo, the influence of propagation effects within these media on tomographic imaging algorithms will be studied and key effects influencing the image quality will be identified. A benchmark environment using synthetic electromagnetic datasets for the evaluation of imaging quality will be developed. Using the obtained results, new models for waves propagating in inhomogeneous materials enabling better imaging quality compared to established approaches will be developed.

Candidates should demonstrate excellent theoretical background in electrodynamics as well as practical proficiencies in the design and fabrication of microwave systems and measurement setups. 

Flight path optimization of UAVs for radar imaging (PostDoc, UUlm, Prof. C. Waldschmidt)

The task of the PostDoc in KoRaTo is to optimize the trajectories of the drones in order to guarantee the optimal imaging quality of the radar sensor network. For this purpose, the topics of SAR imaging and compressed sensing must be considered together, which requires in-depth knowledge of at least in one of the two areas.

The sub-project for the PostDoc is an over-arching project in KoRaTo, which links many other sub-projects with one another. We are therefore looking for personalities who, in addition to excellent scientific knowledge, also have the ability to work in a team and to advance the topic holistically together with the doctoral students.